implement flexbox main axis justification

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Cargo.lock

@@ -1359,10 +1359,38 @@ name = "objc2-core-foundation"
 version = "0.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2a180dd8642fa45cdb7dd721cd4c11b1cadd4929ce112ebd8b9f5803cc79d536"
+dependencies = [
+ "bitflags",
+ "block2",
+ "dispatch2",
+ "libc",
+ "objc2",
+]
+
+[[package]]
+name = "objc2-core-graphics"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e022c9d066895efa1345f8e33e584b9f958da2fd4cd116792e15e07e4720a807"
 dependencies = [
  "bitflags",
  "dispatch2",
  "objc2",
+ "objc2-core-foundation",
+ "objc2-io-surface",
+]
+
+[[package]]
+name = "objc2-core-video"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d425caf1df73233f29fd8a5c3e5edbc30d2d4307870f802d18f00d83dc5141a6"
+dependencies = [
+ "bitflags",
+ "objc2",
+ "objc2-core-foundation",
+ "objc2-core-graphics",
+ "objc2-io-surface",
 ]
 
 [[package]]
@@ -1376,6 +1404,19 @@ name = "objc2-foundation"
 version = "0.3.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e3e0adef53c21f888deb4fa59fc59f7eb17404926ee8a6f59f5df0fd7f9f3272"
+dependencies = [
+ "bitflags",
+ "block2",
+ "libc",
+ "objc2",
+ "objc2-core-foundation",
+]
+
+[[package]]
+name = "objc2-io-surface"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "180788110936d59bab6bd83b6060ffdfffb3b922ba1396b312ae795e1de9d81d"
 dependencies = [
  "bitflags",
  "objc2",
@@ -1401,8 +1442,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "96c1358452b371bf9f104e21ec536d37a650eb10f7ee379fff67d2e08d537f1f"
 dependencies = [
  "bitflags",
+ "block2",
+ "libc",
  "objc2",
  "objc2-core-foundation",
+ "objc2-core-graphics",
+ "objc2-core-video",
  "objc2-foundation",
  "objc2-metal",
 ]
@@ -1883,11 +1928,28 @@ dependencies = [
  "ruin-runtime",
  "ruin_reactivity",
  "ruin_ui",
+ "ruin_ui_platform_macos",
  "ruin_ui_platform_wayland",
  "tracing",
  "tracing-subscriber",
 ]
 
+[[package]]
+name = "ruin_perf"
+version = "0.1.0"
+dependencies = [
+ "serde",
+ "serde_json",
+]
+
+[[package]]
+name = "ruin_perf_scenarios"
+version = "0.1.0"
+dependencies = [
+ "ruin_perf",
+ "ruin_ui",
+]
+
 [[package]]
 name = "ruin_reactivity"
 version = "0.1.0"
@@ -1912,6 +1974,23 @@ dependencies = [
  "tracing-subscriber",
 ]
 
+[[package]]
+name = "ruin_ui_platform_macos"
+version = "0.1.0"
+dependencies = [
+ "libc",
+ "objc2",
+ "objc2-core-foundation",
+ "objc2-foundation",
+ "objc2-quartz-core",
+ "raw-window-handle",
+ "raw-window-metal",
+ "ruin-runtime",
+ "ruin_ui",
+ "ruin_ui_renderer_wgpu",
+ "tracing",
+]
+
 [[package]]
 name = "ruin_ui_platform_wayland"
 version = "0.1.0"

Cargo.toml

@@ -1,3 +1,18 @@
 [workspace]
 resolver = "3"
 members = ["lib/*", "examples/*"]
+default-members = [
+    "lib/reactivity",
+    "lib/reactivity_parsing",
+    "lib/ruin_app",
+    "lib/ruin_app_proc_macros",
+    "lib/runtime",
+    "lib/runtime_proc_macros",
+    "lib/perf",
+    "lib/ui",
+    "lib/ui_platform_macos",
+    "lib/ui_platform_wayland",
+    "lib/ui_renderer_wgpu",
+    "examples/calculator",
+    "examples/perf_scenarios",
+]

docs/performance-profiling.md

@@ -0,0 +1,94 @@
+# Performance profiling workflow
+
+RUIN performance investigations should start with reproducible reports before
+deep profiler sessions. The first-pass tooling is intentionally headless and
+focused on high-signal app-build, layout, text, scene, and cache counters.
+
+## Run a scenario
+
+Use the `ruin_perf_scenarios` package in release mode:
+
+```bash
+cargo run -p ruin_perf_scenarios --release -- \
+  --scenario large-scroll-list \
+  --frames 300 \
+  --output target/ruin-perf/large-scroll-list.json
+```
+
+List available scenarios:
+
+```bash
+cargo run -p ruin_perf_scenarios -- --list
+```
+
+Current scenarios:
+
+| Scenario | What it stresses |
+| --- | --- |
+| `counter` | tiny reactive-style app tree rebuild and layout baseline |
+| `large-scroll-list` | scroll culling, text cache reuse, layout cache behavior |
+| `calculator` | realistic small app tree with display, button grid, and history |
+| `resize-configure` | repeated viewport-size changes and layout reflow |
+| `large-text-body` | huge wrapped text body, text layout cache behavior, scroll clipping |
+
+The large text scenario accepts a body-size option:
+
+```bash
+cargo run -p ruin_perf_scenarios --release -- \
+  --scenario large-text-body \
+  --frames 100 \
+  --text-kb 1024
+```
+
+Each run writes JSON under `target/ruin-perf/` by default and prints a compact
+summary table to stdout.
+
+## Interpreting the report
+
+Start with the timing rows:
+
+- `app_build`: time spent building the deterministic app tree for the frame.
+- `layout_total`: full layout snapshot time.
+- `layout_intrinsic`: intrinsic measurement work inside layout.
+- `text_prepare` / `text_cache_miss`: text shaping/cache miss work.
+
+Then inspect counters:
+
+- High `layout_cache_misses` with low `layout_cache_hits` means the tree or
+  layout constraints are changing in a way that defeats caching.
+- High `viewport_culled` with low `scene_items` is expected for large scroll
+  lists and means scene culling is working.
+- High `text_cache_misses` or `text_cache_miss` time usually means text content,
+  bounds, style, or cache keys are changing too much.
+- Large `scene_items` or `text_glyphs` for tiny workloads suggests excessive UI
+  tree expansion or missing culling.
+
+## Investigation loop
+
+1. Reproduce the suspected degenerate workload with the closest scenario.
+2. Run it in release mode and keep the JSON report.
+3. Compare the stdout summary with a known-good run or a smaller frame count.
+4. If one phase dominates, use an OS profiler on that scenario:
+   - macOS: Instruments Time Profiler / Allocations / Metal System Trace.
+   - Linux: `perf`, `samply`, `heaptrack`, or RenderDoc as appropriate.
+5. After identifying a concrete hot path, add or update a narrow Criterion
+   benchmark before optimizing it.
+
+## Validation
+
+The scenario runner is part of the default workspace. The usual repository
+validation should keep it healthy:
+
+```bash
+cargo test
+cargo clippy --all-targets -- -D warnings
+cargo clippy --release --all-targets -- -D warnings
+```
+
+## Current limitations
+
+This first pass does not automate GUI input, GPU frame capture, or platform
+presentation traces. Renderer frame counters are exposed for platform-backed
+runs, but the headless scenario reports focus on app/layout/text degeneracy
+first. Platform-backed resize/presentation report generation should be added
+after these reports are useful enough to guide concrete optimization work.

examples/calculator/src/components.rs

@@ -28,7 +28,11 @@ pub fn Display(state: CalcState) -> impl IntoView {
         let result = state.result.clone();
         move || {
             let r = result.get();
-            if r.is_empty() { " ".to_string() } else { format!("= {r}") }
+            if r.is_empty() {
+                " ".to_string()
+            } else {
+                format!("= {r}")
+            }
         }
     });
 
@@ -282,9 +286,9 @@ fn mix(base: Color, overlay: Color, amount: f32) -> Color {
 #[component]
 pub fn Keypad(state: CalcState) -> impl IntoView {
     let bg_num = Color::rgba(255, 255, 255, 90);
-    let bg_op  = Color::rgba(210, 230, 255, 140);
+    let bg_op = Color::rgba(210, 230, 255, 140);
-    let bg_eq  = Color::rgba(160, 230, 160, 160);
+    let bg_eq = Color::rgba(160, 230, 160, 160);
-    let bg_fn  = Color::rgba(255, 200, 180, 140);
+    let bg_fn = Color::rgba(255, 200, 180, 140);
 
     macro_rules! digit {
         ($ch:expr) => {{

examples/calculator/src/main.rs

@@ -4,7 +4,7 @@ mod state;
 use ruin_app::prelude::*;
 use tracing_subscriber::layer::SubscriberExt;
 use tracing_subscriber::util::SubscriberInitExt;
-use tracing_subscriber::{EnvFilter, fmt};
+use tracing_subscriber::{fmt, EnvFilter};
 
 use components::{Display, Keypad, ModeToggle, ScientificPanel};
 use state::{CalcMode, CalcState};
@@ -59,32 +59,56 @@ fn CalculatorApp() -> impl IntoView {
         } else {
             display.to_string()
         };
-        use_shortcut(Shortcut::new(Key::Character(ch)), ShortcutScope::Application, {
+        use_shortcut(
-            let text = text.clone();
+            Shortcut::new(Key::Character(ch)),
-            move || s.input(&text)
+            ShortcutScope::Application,
-        });
+            {
+                let text = text.clone();
+                move || s.input(&text)
+            },
+        );
     }
 
     // = key also evaluates
     {
         let s = state.clone();
-        use_shortcut(Shortcut::new(Key::Character('=')), ShortcutScope::Application, move || s.evaluate());
+        use_shortcut(
+            Shortcut::new(Key::Character('=')),
+            ShortcutScope::Application,
+            move || s.evaluate(),
+        );
     }
     {
         let s = state.clone();
-        use_shortcut(Shortcut::new(Key::Enter), ShortcutScope::Application, move || s.evaluate());
+        use_shortcut(
+            Shortcut::new(Key::Enter),
+            ShortcutScope::Application,
+            move || s.evaluate(),
+        );
     }
     {
         let s = state.clone();
-        use_shortcut(Shortcut::new(Key::Backspace), ShortcutScope::Application, move || s.backspace());
+        use_shortcut(
+            Shortcut::new(Key::Backspace),
+            ShortcutScope::Application,
+            move || s.backspace(),
+        );
     }
     {
         let s = state.clone();
-        use_shortcut(Shortcut::new(Key::Escape), ShortcutScope::Application, move || s.clear());
+        use_shortcut(
+            Shortcut::new(Key::Escape),
+            ShortcutScope::Application,
+            move || s.clear(),
+        );
     }
     {
         let s = state.clone();
-        use_shortcut(Shortcut::new(Key::Delete), ShortcutScope::Application, move || s.clear());
+        use_shortcut(
+            Shortcut::new(Key::Delete),
+            ShortcutScope::Application,
+            move || s.clear(),
+        );
     }
 
     // ---- Layout ----
@@ -153,7 +177,7 @@ mod tests {
 
         assert_eq!(state.expression.get(), "4");
         assert_eq!(state.result.get(), "");
-        assert_eq!(state.is_error.get(), false);
+        assert!(!state.is_error.get());
         assert_eq!(state.history.get().len(), 1);
         assert_eq!(state.history.get()[0].expression, "2+2");
         assert_eq!(state.history.get()[0].result, "4");

examples/calculator/src/state.rs

@@ -43,10 +43,10 @@ pub struct CalcState {
 impl CalcState {
     pub fn new() -> Self {
         Self {
-            expression: use_signal(|| String::new()),
+            expression: use_signal(String::new),
-            result: use_signal(|| String::new()),
+            result: use_signal(String::new),
             is_error: use_signal(|| false),
-            history: use_signal(|| Vec::new()),
+            history: use_signal(Vec::new),
             mode: use_signal(|| CalcMode::Basic),
             fresh: use_signal(|| false),
             history_scroll: use_signal(|| 10_000.0_f32),
@@ -77,11 +77,7 @@ impl CalcState {
         }
         self.expression.update(|e| {
             // Pop a full UTF-8 character
-            let new_len = e
+            let new_len = e.char_indices().next_back().map(|(i, _)| i).unwrap_or(0);
-                .char_indices()
-                .next_back()
-                .map(|(i, _)| i)
-                .unwrap_or(0);
             e.truncate(new_len);
         });
     }
@@ -186,7 +182,11 @@ fn format_result(value: f64) -> String {
         return "Error".to_string();
     }
     if value.is_infinite() {
-        return if value > 0.0 { "∞".to_string() } else { "-∞".to_string() };
+        return if value > 0.0 {
+            "∞".to_string()
+        } else {
+            "-∞".to_string()
+        };
     }
     if value.fract() == 0.0 && value.abs() < 1e15 {
         return format!("{}", value as i64);

examples/perf_scenarios/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "ruin_perf_scenarios"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+ruin_perf = { path = "../../lib/perf" }
+ruin_ui = { path = "../../lib/ui" }

examples/perf_scenarios/src/main.rs

@@ -0,0 +1,366 @@
+use std::env;
+use std::io;
+use std::path::PathBuf;
+use std::time::Instant;
+
+use ruin_perf::{PerfReportBuilder, RunMetadata};
+use ruin_ui::{
+    AlignItems, Color, Edges, Element, FlexDirection, LayoutCache, LayoutFrameStats,
+    ScrollbarStyle, TextStyle, TextSystem, UiSize, layout_snapshot_with_cache_and_stats,
+};
+
+const DEFAULT_FRAMES: u64 = 300;
+
+#[derive(Clone, Debug)]
+struct Config {
+    scenario: Scenario,
+    frames: u64,
+    output: Option<PathBuf>,
+    text_kb: usize,
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+enum Scenario {
+    Counter,
+    LargeScrollList,
+    Calculator,
+    ResizeConfigure,
+    LargeTextBody,
+}
+
+impl Scenario {
+    const ALL: &'static [Self] = &[
+        Self::Counter,
+        Self::LargeScrollList,
+        Self::Calculator,
+        Self::ResizeConfigure,
+        Self::LargeTextBody,
+    ];
+
+    const fn name(self) -> &'static str {
+        match self {
+            Self::Counter => "counter",
+            Self::LargeScrollList => "large-scroll-list",
+            Self::Calculator => "calculator",
+            Self::ResizeConfigure => "resize-configure",
+            Self::LargeTextBody => "large-text-body",
+        }
+    }
+
+    fn parse(value: &str) -> Option<Self> {
+        Self::ALL
+            .iter()
+            .copied()
+            .find(|scenario| scenario.name() == value)
+    }
+}
+
+fn main() -> io::Result<()> {
+    let config = Config::parse(env::args().skip(1))?;
+    let report = run_scenario(&config);
+    let output = config
+        .output
+        .clone()
+        .unwrap_or_else(|| report.default_output_path());
+    report.write_json(&output)?;
+    report.print_summary();
+    println!();
+    println!("wrote {}", output.display());
+    Ok(())
+}
+
+impl Config {
+    fn parse(mut args: impl Iterator<Item = String>) -> io::Result<Self> {
+        let mut scenario = Scenario::LargeScrollList;
+        let mut frames = DEFAULT_FRAMES;
+        let mut output = None;
+        let mut text_kb = 256usize;
+
+        while let Some(arg) = args.next() {
+            match arg.as_str() {
+                "--scenario" => {
+                    let value = args.next().ok_or_else(|| {
+                        io::Error::new(io::ErrorKind::InvalidInput, "--scenario needs a value")
+                    })?;
+                    scenario = Scenario::parse(&value).ok_or_else(|| {
+                        io::Error::new(
+                            io::ErrorKind::InvalidInput,
+                            format!("unknown scenario '{value}'"),
+                        )
+                    })?;
+                }
+                "--frames" => {
+                    let value = args.next().ok_or_else(|| {
+                        io::Error::new(io::ErrorKind::InvalidInput, "--frames needs a value")
+                    })?;
+                    frames = value.parse::<u64>().map_err(|error| {
+                        io::Error::new(
+                            io::ErrorKind::InvalidInput,
+                            format!("invalid frame count '{value}': {error}"),
+                        )
+                    })?;
+                }
+                "--output" => {
+                    let value = args.next().ok_or_else(|| {
+                        io::Error::new(io::ErrorKind::InvalidInput, "--output needs a value")
+                    })?;
+                    output = Some(PathBuf::from(value));
+                }
+                "--text-kb" => {
+                    let value = args.next().ok_or_else(|| {
+                        io::Error::new(io::ErrorKind::InvalidInput, "--text-kb needs a value")
+                    })?;
+                    text_kb = value.parse::<usize>().map_err(|error| {
+                        io::Error::new(
+                            io::ErrorKind::InvalidInput,
+                            format!("invalid text size '{value}': {error}"),
+                        )
+                    })?;
+                }
+                "--list" => {
+                    for scenario in Scenario::ALL {
+                        println!("{}", scenario.name());
+                    }
+                    std::process::exit(0);
+                }
+                "--help" | "-h" => {
+                    print_help();
+                    std::process::exit(0);
+                }
+                other => {
+                    return Err(io::Error::new(
+                        io::ErrorKind::InvalidInput,
+                        format!("unknown argument '{other}'"),
+                    ));
+                }
+            }
+        }
+
+        Ok(Self {
+            scenario,
+            frames,
+            output,
+            text_kb,
+        })
+    }
+}
+
+fn print_help() {
+    println!(
+        "ruin_perf_scenarios --scenario <name> [--frames <n>] [--output <path>] [--text-kb <n>]"
+    );
+    println!();
+    println!("scenarios:");
+    for scenario in Scenario::ALL {
+        println!("  {}", scenario.name());
+    }
+}
+
+fn run_scenario(config: &Config) -> ruin_perf::PerfReport {
+    let mut report =
+        PerfReportBuilder::new(RunMetadata::new(config.scenario.name(), config.frames));
+    let mut text_system = TextSystem::new();
+    let mut layout_cache = LayoutCache::new();
+
+    report.note("headless layout/app-build scenario; renderer/platform timings are not included");
+    if config.scenario == Scenario::LargeTextBody {
+        report.set_counter("text_body_kb", config.text_kb as f64);
+    }
+
+    for frame in 0..config.frames {
+        let build_started = Instant::now();
+        let (tree, viewport) = match config.scenario {
+            Scenario::Counter => counter_tree(frame),
+            Scenario::LargeScrollList => large_scroll_list_tree(frame),
+            Scenario::Calculator => calculator_tree(frame),
+            Scenario::ResizeConfigure => resize_configure_tree(frame),
+            Scenario::LargeTextBody => large_text_body_tree(frame, config.text_kb),
+        };
+        let build_ms = build_started.elapsed().as_secs_f64() * 1_000.0;
+        let (_snapshot, stats) = layout_snapshot_with_cache_and_stats(
+            frame + 1,
+            viewport,
+            &tree,
+            &mut text_system,
+            &mut layout_cache,
+        );
+
+        report.record_ms("app_build", build_ms);
+        record_layout_stats(&mut report, stats);
+    }
+
+    report.finish()
+}
+
+fn record_layout_stats(report: &mut PerfReportBuilder, stats: LayoutFrameStats) {
+    report.record_ms("layout_total", stats.total_ms);
+    report.record_ms("layout_intrinsic", stats.intrinsic_ms);
+    report.record_ms("text_prepare", stats.text_prepare_ms);
+    report.record_ms("text_cache_miss", stats.text_miss_ms);
+    report.record("layout_nodes", "count", stats.nodes as f64);
+    report.record("scene_items", "count", stats.scene_items as f64);
+    report.record("text_glyphs", "count", stats.text_output_glyphs as f64);
+    report.add_counter("layout_cache_hits", stats.layout_cache_hits as f64);
+    report.add_counter("layout_cache_misses", stats.layout_cache_misses as f64);
+    report.add_counter("intrinsic_cache_hits", stats.intrinsic_cache_hits as f64);
+    report.add_counter("viewport_culled", stats.viewport_culled as f64);
+    report.add_counter("text_cache_hits", stats.text_cache_hits as f64);
+    report.add_counter("text_cache_misses", stats.text_cache_misses as f64);
+    report.add_counter("text_requests", stats.text_requests as f64);
+}
+
+fn text_style(size: f32) -> TextStyle {
+    TextStyle::new(size, Color::rgb(0x20, 0x20, 0x20))
+}
+
+fn counter_tree(frame: u64) -> (Element, UiSize) {
+    let count = frame as i64;
+    let root = Element::column()
+        .gap(12.0)
+        .padding(Edges::all(24.0))
+        .align_items(AlignItems::Center)
+        .child(Element::text("Counter", text_style(28.0)))
+        .child(Element::text(format!("count = {count}"), text_style(18.0)))
+        .child(Element::text(
+            format!("double = {}", count * 2),
+            text_style(18.0),
+        ))
+        .child(button_row(["-1", "Reset", "+1"]));
+    (root, UiSize::new(480.0, 320.0))
+}
+
+fn large_scroll_list_tree(frame: u64) -> (Element, UiSize) {
+    let item_count = 1_000usize;
+    let item_height = 28.0;
+    let viewport = UiSize::new(480.0, 640.0);
+    let max_offset = (item_count as f32 * item_height - viewport.height).max(0.0);
+    let offset = ((frame as f32 * 19.0) % max_offset.max(1.0)).round();
+    let mut list = Element::column().gap(0.0);
+    for index in 0..item_count {
+        list = list.child(Element::new().height(item_height).child(Element::text(
+            format!("list item {index:04}"),
+            text_style(14.0),
+        )));
+    }
+    let root = Element::new().child(
+        Element::scroll_box(offset)
+            .width(viewport.width)
+            .height(viewport.height)
+            .scrollbar_style(ScrollbarStyle::default())
+            .child(list),
+    );
+    (root, viewport)
+}
+
+fn calculator_tree(frame: u64) -> (Element, UiSize) {
+    let expression = match frame % 6 {
+        0 => "2",
+        1 => "2+",
+        2 => "2+2",
+        3 => "4",
+        4 => "4*8",
+        _ => "32",
+    };
+    let history_len = (frame as usize / 12).min(40);
+    let mut history = Element::column().gap(4.0);
+    for index in 0..history_len {
+        history = history.child(Element::text(
+            format!("{} + {} = {}", index, index + 1, index * 2 + 1),
+            text_style(12.0),
+        ));
+    }
+
+    let root = Element::column()
+        .gap(10.0)
+        .padding(Edges::all(20.0))
+        .child(Element::text("Calculator", text_style(28.0)))
+        .child(display_panel(expression))
+        .child(button_grid())
+        .child(Element::scroll_box(10_000.0).height(180.0).child(history));
+    (root, UiSize::new(420.0, 720.0))
+}
+
+fn resize_configure_tree(frame: u64) -> (Element, UiSize) {
+    let width = 360.0 + (frame % 90) as f32 * 4.0;
+    let height = 280.0 + (frame % 60) as f32 * 3.0;
+    let mut content = Element::column().gap(8.0).padding(Edges::all(16.0));
+    for index in 0..40 {
+        content = content.child(Element::text(
+            format!("resize row {index:02}: {width:.0} x {height:.0}"),
+            text_style(14.0),
+        ));
+    }
+    (content, UiSize::new(width, height))
+}
+
+fn large_text_body_tree(frame: u64, text_kb: usize) -> (Element, UiSize) {
+    let viewport = UiSize::new(720.0, 720.0);
+    let text_width = 680.0;
+    let line_height = 18.0;
+    let text = large_text_body(text_kb);
+    let estimated_line_count = (text.len() as f32 / 72.0).ceil();
+    let estimated_height = (estimated_line_count * line_height).max(viewport.height);
+    let max_offset = (estimated_height - viewport.height).max(0.0);
+    let offset = ((frame as f32 * 127.0) % max_offset.max(1.0)).round();
+    let style = text_style(14.0)
+        .with_line_height(line_height)
+        .with_bounds(UiSize::new(text_width, estimated_height));
+
+    let root = Element::new().child(
+        Element::scroll_box(offset)
+            .width(viewport.width)
+            .height(viewport.height)
+            .child(
+                Element::new()
+                    .width(text_width)
+                    .child(Element::paragraph(text, style)),
+            ),
+    );
+    (root, viewport)
+}
+
+fn large_text_body(text_kb: usize) -> String {
+    let target_bytes = text_kb.saturating_mul(1024).max(1);
+    let paragraph = "RUIN large text profiling paragraph: the quick brown fox jumps over the lazy dog. This line is intentionally ordinary prose with enough words to exercise wrapping, glyph collection, hit-test geometry, and cache behavior.\n";
+    let mut text = String::with_capacity(target_bytes + paragraph.len());
+    while text.len() < target_bytes {
+        text.push_str(paragraph);
+    }
+    text.truncate(target_bytes);
+    text
+}
+
+fn display_panel(expression: &str) -> Element {
+    Element::new()
+        .padding(Edges::all(12.0))
+        .border(1.0, Color::rgb(0x80, 0x80, 0x80))
+        .child(Element::text(expression, text_style(24.0)))
+}
+
+fn button_grid() -> Element {
+    let rows = [
+        ["7", "8", "9", "/"],
+        ["4", "5", "6", "*"],
+        ["1", "2", "3", "-"],
+        ["0", ".", "=", "+"],
+    ];
+    let mut grid = Element::column().gap(6.0);
+    for row in rows {
+        grid = grid.child(button_row(row));
+    }
+    grid
+}
+
+fn button_row<const N: usize>(labels: [&str; N]) -> Element {
+    let mut row = Element::new().direction(FlexDirection::Row).gap(6.0);
+    for label in labels {
+        row = row.child(
+            Element::new()
+                .width(76.0)
+                .height(36.0)
+                .border(1.0, Color::rgb(0x90, 0x90, 0x90))
+                .child(Element::text(label, text_style(16.0))),
+        );
+    }
+    row
+}

lib/perf/Cargo.toml

@@ -0,0 +1,8 @@
+[package]
+name = "ruin_perf"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"

lib/perf/src/lib.rs

@@ -0,0 +1,226 @@
+use std::cmp::Ordering;
+use std::collections::BTreeMap;
+use std::fs;
+use std::io;
+use std::path::{Path, PathBuf};
+use std::time::{Duration, SystemTime, UNIX_EPOCH};
+
+use serde::{Deserialize, Serialize};
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct RunMetadata {
+    pub scenario: String,
+    pub frames: u64,
+    pub profile: String,
+    pub target_os: String,
+    pub target_arch: String,
+    pub started_unix_ms: u128,
+}
+
+impl RunMetadata {
+    pub fn new(scenario: impl Into<String>, frames: u64) -> Self {
+        Self {
+            scenario: scenario.into(),
+            frames,
+            profile: if cfg!(debug_assertions) {
+                "debug".into()
+            } else {
+                "release".into()
+            },
+            target_os: std::env::consts::OS.into(),
+            target_arch: std::env::consts::ARCH.into(),
+            started_unix_ms: SystemTime::now()
+                .duration_since(UNIX_EPOCH)
+                .unwrap_or(Duration::ZERO)
+                .as_millis(),
+        }
+    }
+}
+
+#[derive(Clone, Debug, Default, Serialize, Deserialize)]
+pub struct SampleSeries {
+    pub name: String,
+    pub unit: String,
+    pub samples: Vec<f64>,
+}
+
+impl SampleSeries {
+    pub fn new(name: impl Into<String>, unit: impl Into<String>) -> Self {
+        Self {
+            name: name.into(),
+            unit: unit.into(),
+            samples: Vec::new(),
+        }
+    }
+
+    pub fn push(&mut self, sample: f64) {
+        if sample.is_finite() {
+            self.samples.push(sample);
+        }
+    }
+
+    pub fn summary(&self) -> SampleSummary {
+        SampleSummary::from_samples(&self.name, &self.unit, &self.samples)
+    }
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct SampleSummary {
+    pub name: String,
+    pub unit: String,
+    pub count: usize,
+    pub avg: f64,
+    pub p50: f64,
+    pub p95: f64,
+    pub max: f64,
+}
+
+impl SampleSummary {
+    fn from_samples(name: &str, unit: &str, samples: &[f64]) -> Self {
+        if samples.is_empty() {
+            return Self {
+                name: name.into(),
+                unit: unit.into(),
+                count: 0,
+                avg: 0.0,
+                p50: 0.0,
+                p95: 0.0,
+                max: 0.0,
+            };
+        }
+
+        let mut sorted = samples.to_vec();
+        sorted.sort_by(|a, b| a.partial_cmp(b).unwrap_or(Ordering::Equal));
+        let sum = sorted.iter().sum::<f64>();
+        Self {
+            name: name.into(),
+            unit: unit.into(),
+            count: sorted.len(),
+            avg: sum / sorted.len() as f64,
+            p50: percentile(&sorted, 0.50),
+            p95: percentile(&sorted, 0.95),
+            max: *sorted.last().unwrap_or(&0.0),
+        }
+    }
+}
+
+#[derive(Clone, Debug, Serialize, Deserialize)]
+pub struct PerfReport {
+    pub metadata: RunMetadata,
+    pub summaries: Vec<SampleSummary>,
+    pub counters: BTreeMap<String, f64>,
+    pub notes: Vec<String>,
+}
+
+#[derive(Clone, Debug)]
+pub struct PerfReportBuilder {
+    metadata: RunMetadata,
+    series: BTreeMap<String, SampleSeries>,
+    counters: BTreeMap<String, f64>,
+    notes: Vec<String>,
+}
+
+impl PerfReportBuilder {
+    pub fn new(metadata: RunMetadata) -> Self {
+        Self {
+            metadata,
+            series: BTreeMap::new(),
+            counters: BTreeMap::new(),
+            notes: Vec::new(),
+        }
+    }
+
+    pub fn record_ms(&mut self, name: impl Into<String>, value: f64) {
+        self.record(name, "ms", value);
+    }
+
+    pub fn record(&mut self, name: impl Into<String>, unit: impl Into<String>, value: f64) {
+        let name = name.into();
+        let unit = unit.into();
+        self.series
+            .entry(name.clone())
+            .or_insert_with(|| SampleSeries::new(name, unit))
+            .push(value);
+    }
+
+    pub fn add_counter(&mut self, name: impl Into<String>, value: impl Into<f64>) {
+        *self.counters.entry(name.into()).or_insert(0.0) += value.into();
+    }
+
+    pub fn set_counter(&mut self, name: impl Into<String>, value: impl Into<f64>) {
+        self.counters.insert(name.into(), value.into());
+    }
+
+    pub fn note(&mut self, note: impl Into<String>) {
+        self.notes.push(note.into());
+    }
+
+    pub fn finish(self) -> PerfReport {
+        PerfReport {
+            metadata: self.metadata,
+            summaries: self.series.values().map(SampleSeries::summary).collect(),
+            counters: self.counters,
+            notes: self.notes,
+        }
+    }
+}
+
+impl PerfReport {
+    pub fn write_json(&self, path: impl AsRef<Path>) -> io::Result<()> {
+        let path = path.as_ref();
+        if let Some(parent) = path.parent() {
+            fs::create_dir_all(parent)?;
+        }
+        let json = serde_json::to_string_pretty(self).map_err(io::Error::other)?;
+        fs::write(path, json)?;
+        Ok(())
+    }
+
+    pub fn default_output_path(&self) -> PathBuf {
+        PathBuf::from("target")
+            .join("ruin-perf")
+            .join(format!("{}.json", self.metadata.scenario))
+    }
+
+    pub fn print_summary(&self) {
+        println!(
+            "scenario={} frames={} profile={} target={}/{}",
+            self.metadata.scenario,
+            self.metadata.frames,
+            self.metadata.profile,
+            self.metadata.target_os,
+            self.metadata.target_arch
+        );
+        println!(
+            "{:<32} {:>8} {:>10} {:>10} {:>10} {:>10}",
+            "metric", "count", "avg", "p50", "p95", "max"
+        );
+        for summary in &self.summaries {
+            println!(
+                "{:<32} {:>8} {:>10.3} {:>10.3} {:>10.3} {:>10.3} {}",
+                summary.name,
+                summary.count,
+                summary.avg,
+                summary.p50,
+                summary.p95,
+                summary.max,
+                summary.unit
+            );
+        }
+        if !self.counters.is_empty() {
+            println!();
+            println!("{:<32} {:>12}", "counter", "value");
+            for (name, value) in &self.counters {
+                println!("{name:<32} {value:>12.3}");
+            }
+        }
+    }
+}
+
+fn percentile(sorted: &[f64], percentile: f64) -> f64 {
+    if sorted.is_empty() {
+        return 0.0;
+    }
+    let index = ((sorted.len() - 1) as f64 * percentile).round() as usize;
+    sorted[index.min(sorted.len() - 1)]
+}

lib/reactivity/src/reactor.rs

@@ -290,6 +290,14 @@ impl Reactor {
         self.inner.ensure_flush_scheduled();
     }
 
+    /// Flushes currently queued reactive jobs immediately on the calling thread.
+    ///
+    /// This is useful when host integrations need synchronous propagation
+    /// (for example, during native resize loops).
+    pub fn flush_now(&self) {
+        Rc::clone(&self.inner).flush_jobs();
+    }
+
     pub(crate) fn allocate_node(&self) -> NodeId {
         let raw = self.inner.next_node.get();
         self.inner.next_node.set(raw.wrapping_add(1));

lib/reactivity_parsing/examples/json_reactive_parser.rs

@@ -66,6 +66,13 @@ struct JsonParser {
     next_id: u64,
 }
 
+struct ReuseContext<'a, 'count> {
+    old_text: &'a str,
+    new_text: &'a str,
+    delta: &'a EditDelta,
+    reused: &'count mut usize,
+}
+
 struct Cursor<'a> {
     text: &'a str,
     offset: usize,
@@ -73,10 +80,22 @@ struct Cursor<'a> {
 
 #[derive(Clone)]
 enum Command {
-    Insert { offset: usize, text: String },
+    Insert {
-    Replace { start: usize, end: usize, text: String },
+        offset: usize,
-    ReplaceAll { text: String },
+        text: String,
-    Delete { start: usize, end: usize },
+    },
+    Replace {
+        start: usize,
+        end: usize,
+        text: String,
+    },
+    ReplaceAll {
+        text: String,
+    },
+    Delete {
+        start: usize,
+        end: usize,
+    },
     Print,
     Help,
     Quit,
@@ -102,7 +121,7 @@ async fn main() {
     let parse_state = cell_in(&reactor, initial_snapshot);
     let last_delta = cell_in(&reactor, None::<EditDelta>);
 
-    let _parser_subscription = {
+    {
         let rope = rope.clone();
         let parser = Rc::clone(&parser);
         let parse_state = parse_state.clone();
@@ -130,7 +149,9 @@ async fn main() {
         let parse_state = parse_state.clone();
         let last_delta = last_delta.clone();
         move || {
-            parse_state.with(|snapshot| print_snapshot(snapshot, &rope, last_delta.with(Clone::clone).as_ref()));
+            parse_state.with(|snapshot| {
+                print_snapshot(snapshot, &rope, last_delta.with(Clone::clone).as_ref())
+            });
         }
     })
     .leak();
@@ -199,7 +220,9 @@ fn parse_command(input: &str) -> Result<Command, String> {
             .split_once(' ')
             .ok_or_else(|| "insert expects: insert <offset> <text>".to_string())?;
         return Ok(Command::Insert {
-            offset: offset.parse().map_err(|_| "invalid insert offset".to_string())?,
+            offset: offset
+                .parse()
+                .map_err(|_| "invalid insert offset".to_string())?,
             text: text.to_string(),
         });
     }
@@ -215,7 +238,9 @@ fn parse_command(input: &str) -> Result<Command, String> {
             .next()
             .ok_or_else(|| "replace expects: replace <start> <end> <text>".to_string())?;
         return Ok(Command::Replace {
-            start: start.parse().map_err(|_| "invalid replace start".to_string())?,
+            start: start
+                .parse()
+                .map_err(|_| "invalid replace start".to_string())?,
             end: end.parse().map_err(|_| "invalid replace end".to_string())?,
             text: text.to_string(),
         });
@@ -230,7 +255,9 @@ fn parse_command(input: &str) -> Result<Command, String> {
             .split_once(' ')
             .ok_or_else(|| "delete expects: delete <start> <end>".to_string())?;
         return Ok(Command::Delete {
-            start: start.parse().map_err(|_| "invalid delete start".to_string())?,
+            start: start
+                .parse()
+                .map_err(|_| "invalid delete start".to_string())?,
             end: end.parse().map_err(|_| "invalid delete end".to_string())?,
         });
     }
@@ -263,15 +290,18 @@ impl JsonParser {
         let mut root_anchor = previous.root_anchor;
         root_anchor.map_through(delta);
         let mut reused = 0usize;
+        let mut reuse = ReuseContext {
+            old_text: &previous.text,
+            new_text: &text,
+            delta,
+            reused: &mut reused,
+        };
         let root = self.reuse_node(
             &parsed,
             Some(&previous.root),
             previous.root_anchor.byte,
             root_anchor.byte,
-            &previous.text,
+            &mut reuse,
-            &text,
-            delta,
-            &mut reused,
         );
         Ok(ParseSnapshot {
             text,
@@ -302,20 +332,18 @@ impl JsonParser {
         old: Option<&AstNode>,
         old_parent_start: usize,
         new_parent_start: usize,
-        old_text: &str,
+        reuse: &mut ReuseContext<'_, '_>,
-        new_text: &str,
-        delta: &EditDelta,
-        reused: &mut usize,
     ) -> AstNode {
         let parsed_local = localize(parsed.range, new_parent_start);
         if let Some(old) = old
             && old.kind == parsed.kind
-            && map_range(absolute_range(old, old_parent_start), delta) == parsed.range
+            && map_range(absolute_range(old, old_parent_start), reuse.delta) == parsed.range
-            && old_text
+            && reuse.old_text.get(
-                .get(absolute_range(old, old_parent_start).start..absolute_range(old, old_parent_start).end)
+                absolute_range(old, old_parent_start).start
-                == new_text.get(parsed.range.start..parsed.range.end)
+                    ..absolute_range(old, old_parent_start).end,
+            ) == reuse.new_text.get(parsed.range.start..parsed.range.end)
         {
-            *reused += count_nodes(old);
+            *reuse.reused += count_nodes(old);
             return AstNode {
                 id: old.id,
                 kind: old.kind,
@@ -338,10 +366,7 @@ impl JsonParser {
                     previous_child,
                     next_old_parent_start,
                     parsed.range.start,
-                    old_text,
+                    reuse,
-                    new_text,
-                    delta,
-                    reused,
                 )
             })
             .collect();
@@ -403,7 +428,10 @@ fn parse_json(text: &str) -> Result<ParsedNode, String> {
     let node = cursor.parse_value()?;
     cursor.skip_ws();
     if !cursor.is_eof() {
-        return Err(format!("unexpected trailing data at byte {}", cursor.offset));
+        return Err(format!(
+            "unexpected trailing data at byte {}",
+            cursor.offset
+        ));
     }
     Ok(node)
 }
@@ -496,7 +524,10 @@ impl<'a> Cursor<'a> {
                     break;
                 }
                 Some(other) => {
-                    return Err(format!("expected `,` or `}}` at byte {}, found `{other}`", self.offset));
+                    return Err(format!(
+                        "expected `,` or `}}` at byte {}, found `{other}`",
+                        self.offset
+                    ));
                 }
                 None => return Err("unterminated object".to_string()),
             }
@@ -537,7 +568,10 @@ impl<'a> Cursor<'a> {
                     break;
                 }
                 Some(other) => {
-                    return Err(format!("expected `,` or `]` at byte {}, found `{other}`", self.offset));
+                    return Err(format!(
+                        "expected `,` or `]` at byte {}, found `{other}`",
+                        self.offset
+                    ));
                 }
                 None => return Err("unterminated array".to_string()),
             }
@@ -569,14 +603,24 @@ impl<'a> Cursor<'a> {
                         for _ in 0..4 {
                             match self.bump_char() {
                                 Some(ch) if ch.is_ascii_hexdigit() => {}
-                                _ => return Err(format!("invalid unicode escape at byte {}", self.offset)),
+                                _ => {
+                                    return Err(format!(
+                                        "invalid unicode escape at byte {}",
+                                        self.offset
+                                    ));
+                                }
                             }
                         }
                     }
                     _ => return Err(format!("invalid escape sequence at byte {}", self.offset)),
                 },
                 Some(ch) if ch >= '\u{20}' => {}
-                Some(_) => return Err(format!("control character in string at byte {}", self.offset)),
+                Some(_) => {
+                    return Err(format!(
+                        "control character in string at byte {}",
+                        self.offset
+                    ));
+                }
                 None => return Err("unterminated string".to_string()),
             }
         }

lib/reactivity_parsing/examples/tokentree_reactive_parser.rs

@@ -9,10 +9,22 @@ use ruin_reactivity_parsing::{
 use ruin_runtime::{async_main, fs, stdio};
 
 enum Command {
-    Insert { offset: usize, text: String },
+    Insert {
-    Replace { start: usize, end: usize, text: String },
+        offset: usize,
-    ReplaceAll { text: String },
+        text: String,
-    Delete { start: usize, end: usize },
+    },
+    Replace {
+        start: usize,
+        end: usize,
+        text: String,
+    },
+    ReplaceAll {
+        text: String,
+    },
+    Delete {
+        start: usize,
+        end: usize,
+    },
     Print,
     Help,
     Quit,
@@ -108,7 +120,9 @@ fn parse_command(input: &str) -> Result<Command, String> {
             .split_once(' ')
             .ok_or_else(|| "insert expects: insert <offset> <text>".to_string())?;
         return Ok(Command::Insert {
-            offset: offset.parse().map_err(|_| "invalid insert offset".to_string())?,
+            offset: offset
+                .parse()
+                .map_err(|_| "invalid insert offset".to_string())?,
             text: text.to_string(),
         });
     }
@@ -124,7 +138,9 @@ fn parse_command(input: &str) -> Result<Command, String> {
             .next()
             .ok_or_else(|| "replace expects: replace <start> <end> <text>".to_string())?;
         return Ok(Command::Replace {
-            start: start.parse().map_err(|_| "invalid replace start".to_string())?,
+            start: start
+                .parse()
+                .map_err(|_| "invalid replace start".to_string())?,
             end: end.parse().map_err(|_| "invalid replace end".to_string())?,
             text: text.to_string(),
         });
@@ -139,35 +155,35 @@ fn parse_command(input: &str) -> Result<Command, String> {
             .split_once(' ')
             .ok_or_else(|| "delete expects: delete <start> <end>".to_string())?;
         return Ok(Command::Delete {
-            start: start.parse().map_err(|_| "invalid delete start".to_string())?,
+            start: start
+                .parse()
+                .map_err(|_| "invalid delete start".to_string())?,
             end: end.parse().map_err(|_| "invalid delete end".to_string())?,
         });
     }
     Err("unknown command; type `help`".to_string())
 }
 
-fn print_snapshot(snapshot: &TokenTreeParse, rope: &ReactiveRope, update: Option<&TokenTreeUpdate>) {
+fn print_snapshot(
+    snapshot: &TokenTreeParse,
+    rope: &ReactiveRope,
+    update: Option<&TokenTreeUpdate>,
+) {
     let metrics = rope.snapshot_metrics();
     println!();
     println!("Document revision {}", metrics.revision);
     println!(
         "Text bytes={}, leaves={}, nodes={}, reused_on_last_edit={}",
-        metrics.text.bytes,
+        metrics.text.bytes, metrics.leaves, snapshot.stats.total_nodes, snapshot.stats.reused_nodes
-        metrics.leaves,
-        snapshot.stats.total_nodes,
-        snapshot.stats.reused_nodes
     );
     if let Some(update) = update {
         println!(
             "Last edit: [{}..{}) -> {:?}",
-            update.delta.range.start,
+            update.delta.range.start, update.delta.range.end, update.delta.inserted_text
-            update.delta.range.end,
-            update.delta.inserted_text
         );
         println!(
             "Diagnostics changed={}, trivia changed={}",
-            update.diagnostics_changed,
+            update.diagnostics_changed, update.trivia_changed
-            update.trivia_changed
         );
     }
     println!("Parse tree:");

lib/reactivity_parsing/src/lib.rs

@@ -9,7 +9,7 @@ mod tokentree;
 pub use delta::{Anchor, AnchorBias, EditDelta, RopeEdit, TextRange};
 pub use metrics::{TextMetrics, TextPoint};
 pub use parse::{
-    IncrementalParser, ParseError, ParseInvalidation, ParseResult, ParserCheckpoint, ParseTree,
+    IncrementalParser, ParseError, ParseInvalidation, ParseResult, ParseTree, ParserCheckpoint,
     SyntaxFragment,
 };
 pub use rope::{
@@ -17,8 +17,8 @@ pub use rope::{
     RopeSnapshotMetrics,
 };
 pub use tokentree::{
-    DelimiterKind, NumberBase, NumberLiteral, NumberSuffix, StringDelimiter, StringFragment,
+    DelimiterKind, NumberBase, NumberLiteral, NumberSuffix, ReactiveTokenTree, StringDelimiter,
-    ReactiveTokenTree, TokenTreeDiagnostic, TokenTreeDiagnosticKind, TokenTreeNode,
+    StringFragment, TokenTreeDiagnostic, TokenTreeDiagnosticKind, TokenTreeNode, TokenTreeNodeKind,
-    TokenTreeNodeKind, TokenTreeParse, TokenTreeParser, TokenTreeStats, TokenTreeUpdate,
+    TokenTreeParse, TokenTreeParser, TokenTreeStats, TokenTreeUpdate, TriviaComment, TriviaKind,
-    TriviaComment, TriviaKind, TriviaStore,
+    TriviaStore,
 };

lib/reactivity_parsing/src/parse.rs

@@ -38,6 +38,8 @@ pub struct ParseError {
     pub message: String,
 }
 
+pub type ParserResult<C, T, D> = Result<ParseResult<C, T, D>, ParseError>;
+
 impl ParseError {
     pub fn new(message: impl Into<String>) -> Self {
         Self {
@@ -66,7 +68,7 @@ pub trait IncrementalParser {
         cursor: RopeCursor,
         fragments: &[SyntaxFragment<Self::Checkpoint, Self::Tree, Self::Diagnostic>],
         invalidation: ParseInvalidation<Self::Checkpoint>,
-    ) -> Result<ParseResult<Self::Checkpoint, Self::Tree, Self::Diagnostic>, ParseError>;
+    ) -> ParserResult<Self::Checkpoint, Self::Tree, Self::Diagnostic>;
 }
 
 #[cfg(test)]
@@ -102,7 +104,11 @@ mod tests {
         fn invalidate(
             &self,
             delta_range: TextRange,
-            _previous_fragments: &[SyntaxFragment<Self::Checkpoint, Self::Tree, Self::Diagnostic>],
+            _previous_fragments: &[SyntaxFragment<
+                Self::Checkpoint,
+                Self::Tree,
+                Self::Diagnostic,
+            >],
         ) -> ParseInvalidation<Self::Checkpoint> {
             ParseInvalidation {
                 resume_at: delta_range.start.saturating_sub(1),
@@ -115,13 +121,17 @@ mod tests {
             mut cursor: RopeCursor,
             _fragments: &[SyntaxFragment<Self::Checkpoint, Self::Tree, Self::Diagnostic>],
             invalidation: ParseInvalidation<Self::Checkpoint>,
-        ) -> Result<ParseResult<Self::Checkpoint, Self::Tree, Self::Diagnostic>, ParseError> {
+        ) -> Result<ParseResult<Self::Checkpoint, Self::Tree, Self::Diagnostic>, ParseError>
+        {
             self.parse_calls.set(self.parse_calls.get() + 1);
             let text = cursor.read_bytes(usize::MAX);
             Ok(ParseResult {
                 tree: ParseTree { root: text.clone() },
                 fragments: vec![SyntaxFragment {
-                    range: TextRange::new(invalidation.resume_at, invalidation.resume_at + text.len()),
+                    range: TextRange::new(
+                        invalidation.resume_at,
+                        invalidation.resume_at + text.len(),
+                    ),
                     start_checkpoint: invalidation.restart_checkpoint,
                     end_checkpoint: 2,
                     tree: text,

lib/reactivity_parsing/src/rope.rs

@@ -1,6 +1,7 @@
 use std::cell::{Cell, RefCell};
 use std::cmp::min;
 use std::collections::BTreeSet;
+use std::fmt;
 use std::rc::Rc;
 
 use ruin_reactivity::{Event, Reactor, Source, event_in, source_in};
@@ -139,10 +140,6 @@ impl ReactiveRope {
         self.len_bytes() == 0
     }
 
-    pub fn to_string(&self) -> String {
-        self.slice(TextRange::new(0, self.len_bytes()))
-    }
-
     pub fn point_at(&self, offset: usize) -> TextPoint {
         self.inner.structure.observe();
         let offset = offset.min(self.len_bytes());
@@ -259,7 +256,10 @@ impl ReactiveRope {
 
     fn apply_edit(&self, edit: RopeEdit) -> EditDelta {
         assert!(edit.range.start <= edit.range.end, "invalid edit range");
-        assert!(edit.range.end <= self.len_bytes(), "edit range out of bounds");
+        assert!(
+            edit.range.end <= self.len_bytes(),
+            "edit range out of bounds"
+        );
         self.assert_char_boundary(edit.range.start);
         self.assert_char_boundary(edit.range.end);
         assert!(
@@ -304,7 +304,8 @@ impl ReactiveRope {
         replacement.push_str(&edit.insert);
         replacement.push_str(&suffix);
 
-        let structure_changed = last_index > first_index || replacement.len() > DEFAULT_LEAF_MAX_BYTES;
+        let structure_changed =
+            last_index > first_index || replacement.len() > DEFAULT_LEAF_MAX_BYTES;
         if !structure_changed {
             if let Some(leaf) = leaves.get(first_index) {
                 leaf.set_text(replacement);
@@ -338,7 +339,9 @@ impl ReactiveRope {
             self.inner.structure.trigger();
         }
 
-        self.inner.revision.set(self.inner.revision.get().wrapping_add(1));
+        self.inner
+            .revision
+            .set(self.inner.revision.get().wrapping_add(1));
 
         let new_end = old_start.advance(&edit.insert);
         drop(leaves);
@@ -399,7 +402,10 @@ impl ReactiveRope {
             let end = cursor + bytes;
             if offset < end {
                 let text = leaf.read();
-                assert!(text.is_char_boundary(offset - cursor), "offset must be a char boundary");
+                assert!(
+                    text.is_char_boundary(offset - cursor),
+                    "offset must be a char boundary"
+                );
                 return;
             }
             cursor = end;
@@ -407,6 +413,12 @@ impl ReactiveRope {
     }
 }
 
+impl fmt::Display for ReactiveRope {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(&self.slice(TextRange::new(0, self.len_bytes())))
+    }
+}
+
 impl RopeChunk {
     pub fn text(&self) -> &str {
         &self.text
@@ -710,7 +722,10 @@ mod tests {
         let seen = Rc::new(RefCell::new(Vec::new()));
         let _sub = rope.edit_events().subscribe({
             let seen = Rc::clone(&seen);
-            move |delta| seen.borrow_mut().push((delta.range, delta.inserted_text.clone()))
+            move |delta| {
+                seen.borrow_mut()
+                    .push((delta.range, delta.inserted_text.clone()))
+            }
         });
 
         rope.edit(RopeEdit::insert(1, "Z"));

lib/reactivity_parsing/src/tokentree.rs

@@ -7,9 +7,9 @@ use ruin_reactivity::{Cell, Event, Subscription, cell_in, event_in};
 use crate::{Anchor, AnchorBias, EditDelta, ReactiveRope, TextPoint, TextRange};
 
 const SIGILS: &[&str] = &[
-    "<<=", ">>=", "..=", "::", "->", "=>", "==", "!=", "<=", ">=", "&&", "||", "+=", "-=",
+    "<<=", ">>=", "..=", "::", "->", "=>", "==", "!=", "<=", ">=", "&&", "||", "+=", "-=", "*=",
-    "*=", "/=", "%=", "&=", "|=", "^=", "<<", ">>", "..", "+", "-", "*", "/", "%", "&", "|",
+    "/=", "%=", "&=", "|=", "^=", "<<", ">>", "..", "+", "-", "*", "/", "%", "&", "|", "^", "!",
-    "^", "!", "~", "=", "<", ">", ":", ";", "?", ".", ",", "@", "#", "$",
+    "~", "=", "<", ">", ":", ";", "?", ".", ",", "@", "#", "$",
 ];
 
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
@@ -28,8 +28,14 @@ pub enum StringDelimiter {
 
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub enum StringFragment {
-    Text { range: TextRange, text: String },
+    Text {
-    Interpolation { range: TextRange, child_index: usize },
+        range: TextRange,
+        text: String,
+    },
+    Interpolation {
+        range: TextRange,
+        child_index: usize,
+    },
 }
 
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
@@ -317,6 +323,13 @@ pub struct TokenTreeParser {
     next_id: u64,
 }
 
+struct ReuseContext<'a, 'count> {
+    old_text: &'a str,
+    new_text: &'a str,
+    delta: &'a EditDelta,
+    reused_nodes: &'count mut usize,
+}
+
 impl TokenTreeParser {
     pub fn new() -> Self {
         Self::default()
@@ -352,15 +365,18 @@ impl TokenTreeParser {
         let mut root_anchor = previous.root_anchor;
         root_anchor.map_through(delta);
         let mut reused_nodes = 0usize;
+        let mut reuse = ReuseContext {
+            old_text: &previous.text,
+            new_text: &text,
+            delta,
+            reused_nodes: &mut reused_nodes,
+        };
         let root = self.reuse_node(
             &raw.root,
             Some(&previous.root),
             previous.root_anchor.byte,
             root_anchor.byte,
-            &previous.text,
+            &mut reuse,
-            &text,
-            delta,
-            &mut reused_nodes,
         );
         let total_nodes = count_nodes(&root);
 
@@ -397,14 +413,20 @@ impl TokenTreeParser {
         old: Option<&TokenTreeNode>,
         old_parent_start: usize,
         new_parent_start: usize,
-        old_text: &str,
+        reuse: &mut ReuseContext<'_, '_>,
-        new_text: &str,
-        delta: &EditDelta,
-        reused_nodes: &mut usize,
     ) -> TokenTreeNode {
         let parsed_local = localize(parsed.range, new_parent_start);
-        if let Some(old) = old.filter(|old| can_reuse_node(old, old_parent_start, parsed, old_text, new_text, delta)) {
+        if let Some(old) = old.filter(|old| {
-            *reused_nodes += count_nodes(old);
+            can_reuse_node(
+                old,
+                old_parent_start,
+                parsed,
+                reuse.old_text,
+                reuse.new_text,
+                reuse.delta,
+            )
+        }) {
+            *reuse.reused_nodes += count_nodes(old);
             return TokenTreeNode {
                 id: old.id,
                 local_range: parsed_local,
@@ -423,24 +445,22 @@ impl TokenTreeParser {
                     let candidate = old
                         .children
                         .get(index)
-                        .filter(|candidate| {
+                        .filter(|candidate| !used[index] && can_descend_into_node(candidate, child))
-                            !used[index]
+                        .inspect(|_| {
-                                && can_descend_into_node(candidate, child)
-                        })
-                        .map(|candidate| {
                             used[index] = true;
-                            candidate
                         })
                         .or_else(|| {
-                            old.children.iter().enumerate().find_map(|(candidate_index, candidate)| {
+                            old.children.iter().enumerate().find_map(
-                                if used[candidate_index]
+                                |(candidate_index, candidate)| {
-                                    || !can_descend_into_node(candidate, child)
+                                    if used[candidate_index]
-                                {
+                                        || !can_descend_into_node(candidate, child)
-                                    return None;
+                                    {
-                                }
+                                        return None;
-                                used[candidate_index] = true;
+                                    }
-                                Some(candidate)
+                                    used[candidate_index] = true;
-                            })
+                                    Some(candidate)
+                                },
+                            )
                         });
 
                     self.reuse_node(
@@ -448,10 +468,7 @@ impl TokenTreeParser {
                         candidate,
                         absolute_range(old, old_parent_start).start,
                         parsed.range.start,
-                        old_text,
+                        reuse,
-                        new_text,
-                        delta,
-                        reused_nodes,
                     )
                 })
                 .collect()
@@ -460,16 +477,7 @@ impl TokenTreeParser {
                 .children
                 .iter()
                 .map(|child| {
-                    self.reuse_node(
+                    self.reuse_node(child, None, old_parent_start, parsed.range.start, reuse)
-                        child,
-                        None,
-                        old_parent_start,
-                        parsed.range.start,
-                        old_text,
-                        new_text,
-                        delta,
-                        reused_nodes,
-                    )
                 })
                 .collect()
         };
@@ -538,12 +546,12 @@ impl<'a> Cursor<'a> {
                 break;
             }
 
-            if let Some(close) = terminator {
+            if let Some(close) = terminator
-                if self.peek_char() == Some(close) {
+                && self.peek_char() == Some(close)
-                    self.bump_char();
+            {
-                    terminated = true;
+                self.bump_char();
-                    break;
+                terminated = true;
-                }
+                break;
             }
 
             let Some(ch) = self.peek_char() else {
@@ -602,8 +610,8 @@ impl<'a> Cursor<'a> {
         let (_, close) = delimiter_chars(delimiter);
         self.bump_char();
         let children = self.parse_sequence(Some(close));
-        let terminated =
+        let terminated = self.slice(self.offset.saturating_sub(close.len_utf8()), self.offset)
-            self.slice(self.offset.saturating_sub(close.len_utf8()), self.offset) == close.to_string();
+            == close.to_string();
         RawNode {
             range: TextRange::new(start, self.offset),
             kind: TokenTreeNodeKind::List {
@@ -667,7 +675,9 @@ impl<'a> Cursor<'a> {
 
     fn parse_string(&mut self) -> RawNode {
         let start = self.offset;
-        let delimiter_char = self.bump_char().expect("string should start with delimiter");
+        let delimiter_char = self
+            .bump_char()
+            .expect("string should start with delimiter");
         let delimiter = match delimiter_char {
             '\'' => StringDelimiter::SingleQuote,
             '"' => StringDelimiter::DoubleQuote,
@@ -702,9 +712,8 @@ impl<'a> Cursor<'a> {
                 let interp_start = self.offset;
                 self.offset += 2;
                 let interpolation_children = self.parse_sequence(Some(')'));
-                let terminated_interp = self
+                let terminated_interp =
-                    .slice(self.offset.saturating_sub(1), self.offset)
+                    self.slice(self.offset.saturating_sub(1), self.offset) == ")";
-                    == ")";
                 if !terminated_interp {
                     self.diagnostics.push(TokenTreeDiagnostic {
                         kind: TokenTreeDiagnosticKind::UnterminatedInterpolation,
@@ -972,7 +981,11 @@ impl<'a> Cursor<'a> {
     fn scan_number(
         &self,
         start: usize,
-    ) -> (NumberLiteral, usize, Option<(TokenTreeDiagnosticKind, String)>) {
+    ) -> (
+        NumberLiteral,
+        usize,
+        Option<(TokenTreeDiagnosticKind, String)>,
+    ) {
         let mut cursor = start;
         let mut base = NumberBase::Decimal;
         if self.starts_with_at(start, "0b") {
@@ -1190,14 +1203,17 @@ fn can_reuse_node(
     let old_abs = absolute_range(old, old_parent_start);
     old.kind == parsed.kind
         && map_range(old_abs, delta) == parsed.range
-        && old_text.get(old_abs.start..old_abs.end) == new_text.get(parsed.range.start..parsed.range.end)
+        && old_text.get(old_abs.start..old_abs.end)
+            == new_text.get(parsed.range.start..parsed.range.end)
 }
 
 fn can_descend_into_node(old: &TokenTreeNode, parsed: &RawNode) -> bool {
     match (&old.kind, &parsed.kind) {
         (TokenTreeNodeKind::Body, TokenTreeNodeKind::Body) => true,
         (
-            TokenTreeNodeKind::List { delimiter: left, .. },
+            TokenTreeNodeKind::List {
+                delimiter: left, ..
+            },
             TokenTreeNodeKind::List {
                 delimiter: right, ..
             },
@@ -1225,15 +1241,12 @@ fn count_nodes(node: &TokenTreeNode) -> usize {
     1 + node.children.iter().map(count_nodes).sum::<usize>()
 }
 
-fn number_body_valid(
+fn number_body_valid(raw: &str, base: NumberBase, saw_radix: bool, suffix_start: usize) -> bool {
-    raw: &str,
-    base: NumberBase,
-    saw_radix: bool,
-    suffix_start: usize,
-) -> bool {
     let mut body = &raw[..suffix_start];
-    if matches!(base, NumberBase::Binary | NumberBase::Octal | NumberBase::Decimal | NumberBase::Hexadecimal)
+    if matches!(
-        && body.starts_with("0")
+        base,
+        NumberBase::Binary | NumberBase::Octal | NumberBase::Decimal | NumberBase::Hexadecimal
+    ) && body.starts_with("0")
         && body.len() >= 2
         && matches!(body.as_bytes()[1], b'b' | b'o' | b'd' | b'x')
     {
@@ -1334,12 +1347,15 @@ mod tests {
     }
 
     fn node_text<'a>(parse: &'a TokenTreeParse, node: &TokenTreeNode) -> &'a str {
-        let range = parse.absolute_range(node.id).expect("node should have absolute range");
+        let range = parse
+            .absolute_range(node.id)
+            .expect("node should have absolute range");
         &parse.text()[range.start..range.end]
     }
 
     fn symbol_texts(parse: &TokenTreeParse) -> Vec<&str> {
-        parse.root
+        parse
+            .root
             .children
             .iter()
             .filter_map(|node| match &node.kind {
@@ -1350,7 +1366,8 @@ mod tests {
     }
 
     fn sigil_texts(parse: &TokenTreeParse) -> Vec<&str> {
-        parse.root
+        parse
+            .root
             .children
             .iter()
             .filter_map(|node| match &node.kind {
@@ -1360,7 +1377,7 @@ mod tests {
             .collect()
     }
 
-    fn find_list_child<'a>(node: &'a TokenTreeNode, delimiter: DelimiterKind) -> &'a TokenTreeNode {
+    fn find_list_child(node: &TokenTreeNode, delimiter: DelimiterKind) -> &TokenTreeNode {
         node.children
             .iter()
             .find(|child| {
@@ -1376,7 +1393,11 @@ mod tests {
     }
 
     fn diagnostic_kinds(parse: &TokenTreeParse) -> Vec<TokenTreeDiagnosticKind> {
-        parse.diagnostics.iter().map(|diagnostic| diagnostic.kind).collect()
+        parse
+            .diagnostics
+            .iter()
+            .map(|diagnostic| diagnostic.kind)
+            .collect()
     }
 
     #[test]
@@ -1399,11 +1420,26 @@ mod tests {
     fn parses_mixed_top_level_sequence_in_order() {
         let parse = parse_text("alpha + 12 \"hi\" [beta]");
         assert_eq!(parse.root.children.len(), 5);
-        assert!(matches!(parse.root.children[0].kind, TokenTreeNodeKind::Symbol { .. }));
+        assert!(matches!(
-        assert!(matches!(parse.root.children[1].kind, TokenTreeNodeKind::Sigil { .. }));
+            parse.root.children[0].kind,
-        assert!(matches!(parse.root.children[2].kind, TokenTreeNodeKind::Number(..)));
+            TokenTreeNodeKind::Symbol { .. }
-        assert!(matches!(parse.root.children[3].kind, TokenTreeNodeKind::String { .. }));
+        ));
-        assert!(matches!(parse.root.children[4].kind, TokenTreeNodeKind::List { .. }));
+        assert!(matches!(
+            parse.root.children[1].kind,
+            TokenTreeNodeKind::Sigil { .. }
+        ));
+        assert!(matches!(
+            parse.root.children[2].kind,
+            TokenTreeNodeKind::Number(..)
+        ));
+        assert!(matches!(
+            parse.root.children[3].kind,
+            TokenTreeNodeKind::String { .. }
+        ));
+        assert!(matches!(
+            parse.root.children[4].kind,
+            TokenTreeNodeKind::List { .. }
+        ));
     }
 
     #[test]
@@ -1418,12 +1454,24 @@ mod tests {
             }
         ));
         let outer = &parse.root.children[0];
-        assert!(matches!(outer.children[0].kind, TokenTreeNodeKind::Symbol { .. }));
+        assert!(matches!(
+            outer.children[0].kind,
+            TokenTreeNodeKind::Symbol { .. }
+        ));
         let inner_paren = find_list_child(outer, DelimiterKind::Parenthesis);
-        assert!(matches!(inner_paren.children[0].kind, TokenTreeNodeKind::Symbol { .. }));
+        assert!(matches!(
-        assert!(matches!(inner_paren.children[1].kind, TokenTreeNodeKind::Sigil { .. }));
+            inner_paren.children[0].kind,
+            TokenTreeNodeKind::Symbol { .. }
+        ));
+        assert!(matches!(
+            inner_paren.children[1].kind,
+            TokenTreeNodeKind::Sigil { .. }
+        ));
         let inner_bracket = find_list_child(inner_paren, DelimiterKind::Bracket);
-        assert!(matches!(inner_bracket.children[0].kind, TokenTreeNodeKind::Symbol { .. }));
+        assert!(matches!(
+            inner_bracket.children[0].kind,
+            TokenTreeNodeKind::Symbol { .. }
+        ));
     }
 
     #[test]
@@ -1491,9 +1539,18 @@ mod tests {
                 TokenTreeDiagnosticKind::UnmatchedClosingDelimiter,
             ]
         );
-        assert!(matches!(parse.root.children[0].kind, TokenTreeNodeKind::Error { .. }));
+        assert!(matches!(
-        assert!(matches!(parse.root.children[1].kind, TokenTreeNodeKind::Symbol { .. }));
+            parse.root.children[0].kind,
-        assert!(matches!(parse.root.children[2].kind, TokenTreeNodeKind::Error { .. }));
+            TokenTreeNodeKind::Error { .. }
+        ));
+        assert!(matches!(
+            parse.root.children[1].kind,
+            TokenTreeNodeKind::Symbol { .. }
+        ));
+        assert!(matches!(
+            parse.root.children[2].kind,
+            TokenTreeNodeKind::Error { .. }
+        ));
     }
 
     #[test]
@@ -1514,8 +1571,14 @@ mod tests {
                 terminated: false
             }
         ));
-        assert!(matches!(list.children[0].kind, TokenTreeNodeKind::Symbol { .. }));
+        assert!(matches!(
-        assert!(matches!(list.children[1].kind, TokenTreeNodeKind::Error { .. }));
+            list.children[0].kind,
+            TokenTreeNodeKind::Symbol { .. }
+        ));
+        assert!(matches!(
+            list.children[1].kind,
+            TokenTreeNodeKind::Error { .. }
+        ));
     }
 
     #[test]
@@ -1525,8 +1588,14 @@ mod tests {
             diagnostic_kinds(&parse),
             vec![TokenTreeDiagnosticKind::UnmatchedClosingDelimiter]
         );
-        assert!(matches!(parse.root.children[0].kind, TokenTreeNodeKind::List { .. }));
+        assert!(matches!(
-        assert!(matches!(parse.root.children[1].kind, TokenTreeNodeKind::Error { .. }));
+            parse.root.children[0].kind,
+            TokenTreeNodeKind::List { .. }
+        ));
+        assert!(matches!(
+            parse.root.children[1].kind,
+            TokenTreeNodeKind::Error { .. }
+        ));
     }
 
     #[test]
@@ -1546,7 +1615,10 @@ mod tests {
         let parse = parse_text("left+right(foo)");
         assert_eq!(symbol_texts(&parse), vec!["left", "right"]);
         assert_eq!(sigil_texts(&parse), vec!["+"]);
-        assert!(matches!(parse.root.children[3].kind, TokenTreeNodeKind::List { .. }));
+        assert!(matches!(
+            parse.root.children[3].kind,
+            TokenTreeNodeKind::List { .. }
+        ));
     }
 
     #[test]
@@ -1556,14 +1628,21 @@ mod tests {
             diagnostic_kinds(&parse),
             vec![TokenTreeDiagnosticKind::InvalidNumber]
         );
-        assert!(matches!(parse.root.children[0].kind, TokenTreeNodeKind::Error { .. }));
+        assert!(matches!(
+            parse.root.children[0].kind,
+            TokenTreeNodeKind::Error { .. }
+        ));
     }
 
     #[test]
     fn every_defined_sigil_parses_as_a_sigil_node() {
         for sigil in SIGILS {
             let parse = parse_text(sigil);
-            assert_eq!(parse.root.children.len(), 1, "sigil `{sigil}` should be a single token");
+            assert_eq!(
+                parse.root.children.len(),
+                1,
+                "sigil `{sigil}` should be a single token"
+            );
             assert!(
                 matches!(
                     &parse.root.children[0].kind,
@@ -1592,8 +1671,14 @@ mod tests {
     fn preserves_comments_as_trivia() {
         let parse = parse_text("foo // hi\n/* block */ bar");
         assert_eq!(parse.trivia.comments().len(), 2);
-        assert!(matches!(parse.root.children[0].kind, TokenTreeNodeKind::Symbol { .. }));
+        assert!(matches!(
-        assert!(matches!(parse.root.children[1].kind, TokenTreeNodeKind::Symbol { .. }));
+            parse.root.children[0].kind,
+            TokenTreeNodeKind::Symbol { .. }
+        ));
+        assert!(matches!(
+            parse.root.children[1].kind,
+            TokenTreeNodeKind::Symbol { .. }
+        ));
     }
 
     #[test]
@@ -1602,7 +1687,10 @@ mod tests {
         assert!(parse.diagnostics.is_empty());
         assert_eq!(parse.trivia.comments().len(), 1);
         assert_eq!(parse.trivia.comments()[0].kind, TriviaKind::BlockComment);
-        assert_eq!(parse.trivia.comments()[0].text, "/* outer /* inner */ done */");
+        assert_eq!(
+            parse.trivia.comments()[0].text,
+            "/* outer /* inner */ done */"
+        );
     }
 
     #[test]
@@ -1621,7 +1709,9 @@ mod tests {
         let parse = parse_text("foo // hi\nbar /* block */ baz");
         let line = &parse.trivia.comments()[0];
         let block = &parse.trivia.comments()[1];
-        let overlapping = parse.trivia.comments_in_range(TextRange::new(line.range.start, block.range.end));
+        let overlapping = parse
+            .trivia
+            .comments_in_range(TextRange::new(line.range.start, block.range.end));
         assert_eq!(overlapping.len(), 2);
         let before_block = parse.trivia.comments_before(block.range.start);
         assert_eq!(before_block.len(), 1);
@@ -1721,7 +1811,10 @@ mod tests {
         );
         assert!(matches!(
             parse.root.children[0].kind,
-            TokenTreeNodeKind::String { terminated: true, .. }
+            TokenTreeNodeKind::String {
+                terminated: true,
+                ..
+            }
         ));
     }
 
@@ -1754,9 +1847,15 @@ mod tests {
                 assert_eq!(fragments.len(), 4);
                 assert_eq!(string.children.len(), 2);
                 assert!(matches!(fragments[0], StringFragment::Text { .. }));
-                assert!(matches!(fragments[1], StringFragment::Interpolation { child_index: 0, .. }));
+                assert!(matches!(
+                    fragments[1],
+                    StringFragment::Interpolation { child_index: 0, .. }
+                ));
                 assert!(matches!(fragments[2], StringFragment::Text { .. }));
-                assert!(matches!(fragments[3], StringFragment::Interpolation { child_index: 1, .. }));
+                assert!(matches!(
+                    fragments[3],
+                    StringFragment::Interpolation { child_index: 1, .. }
+                ));
                 assert!(matches!(
                     string.children[0].kind,
                     TokenTreeNodeKind::List {
@@ -1784,7 +1883,10 @@ mod tests {
             TokenTreeNodeKind::String { fragments, .. } => {
                 assert_eq!(fragments.len(), 2);
                 assert_eq!(string.children.len(), 1);
-                assert!(matches!(string.children[0].kind, TokenTreeNodeKind::List { .. }));
+                assert!(matches!(
+                    string.children[0].kind,
+                    TokenTreeNodeKind::List { .. }
+                ));
             }
             other => panic!("expected string, got {other:?}"),
         }
@@ -1818,19 +1920,52 @@ mod tests {
     fn parses_numbers_with_supported_bases_and_suffixes() {
         let cases = [
             ("0", NumberBase::Decimal, false, None),
-            ("12.3f64", NumberBase::Decimal, true, Some(NumberSuffix::F64)),
+            (
+                "12.3f64",
+                NumberBase::Decimal,
+                true,
+                Some(NumberSuffix::F64),
+            ),
             ("0d1_2_3", NumberBase::Decimal, false, None),
-            ("0b1010u8", NumberBase::Binary, false, Some(NumberSuffix::U8)),
+            (
+                "0b1010u8",
+                NumberBase::Binary,
+                false,
+                Some(NumberSuffix::U8),
+            ),
             ("0o77i16", NumberBase::Octal, false, Some(NumberSuffix::I16)),
-            ("0xffu", NumberBase::Hexadecimal, false, Some(NumberSuffix::BigUint)),
+            (
-            ("99d", NumberBase::Decimal, false, Some(NumberSuffix::BigDecimal)),
+                "0xffu",
-            ("42d128", NumberBase::Decimal, false, Some(NumberSuffix::Decimal128)),
+                NumberBase::Hexadecimal,
-            ("5f", NumberBase::Decimal, false, Some(NumberSuffix::BigFloat)),
+                false,
+                Some(NumberSuffix::BigUint),
+            ),
+            (
+                "99d",
+                NumberBase::Decimal,
+                false,
+                Some(NumberSuffix::BigDecimal),
+            ),
+            (
+                "42d128",
+                NumberBase::Decimal,
+                false,
+                Some(NumberSuffix::Decimal128),
+            ),
+            (
+                "5f",
+                NumberBase::Decimal,
+                false,
+                Some(NumberSuffix::BigFloat),
+            ),
         ];
 
         for (text, base, has_radix_point, suffix) in cases {
             let parse = parse_text(text);
-            assert!(parse.diagnostics.is_empty(), "unexpected diagnostics for `{text}`");
+            assert!(
+                parse.diagnostics.is_empty(),
+                "unexpected diagnostics for `{text}`"
+            );
             match &parse.root.children[0].kind {
                 TokenTreeNodeKind::Number(number) => {
                     assert_eq!(number.raw, text);
@@ -1848,7 +1983,13 @@ mod tests {
         let parse = parse_text("1_2_3 0x_ff 0d12_.3f64 1._5");
         assert!(parse.diagnostics.is_empty());
         assert_eq!(parse.root.children.len(), 4);
-        assert!(parse.root.children.iter().all(|node| matches!(node.kind, TokenTreeNodeKind::Number(..))));
+        assert!(
+            parse
+                .root
+                .children
+                .iter()
+                .all(|node| matches!(node.kind, TokenTreeNodeKind::Number(..)))
+        );
     }
 
     #[test]
@@ -1858,7 +1999,10 @@ mod tests {
             diagnostic_kinds(&parse),
             vec![TokenTreeDiagnosticKind::InvalidNumber]
         );
-        assert!(matches!(parse.root.children[0].kind, TokenTreeNodeKind::Error { .. }));
+        assert!(matches!(
+            parse.root.children[0].kind,
+            TokenTreeNodeKind::Error { .. }
+        ));
     }
 
     #[test]
@@ -1872,28 +2016,52 @@ mod tests {
                 TokenTreeDiagnosticKind::InvalidNumber,
             ]
         );
-        assert!(parse.root.children.iter().all(|node| matches!(node.kind, TokenTreeNodeKind::Error { .. })));
+        assert!(
+            parse
+                .root
+                .children
+                .iter()
+                .all(|node| matches!(node.kind, TokenTreeNodeKind::Error { .. }))
+        );
     }
 
     #[test]
     fn numbers_reject_unknown_or_underscored_suffixes() {
         let parse = parse_text("12foo 9u_8");
-        assert_eq!(diagnostic_kinds(&parse), vec![TokenTreeDiagnosticKind::InvalidNumber]);
+        assert_eq!(
-        assert!(matches!(parse.root.children[0].kind, TokenTreeNodeKind::Error { .. }));
+            diagnostic_kinds(&parse),
-        assert!(matches!(parse.root.children[1].kind, TokenTreeNodeKind::Number(..)));
+            vec![TokenTreeDiagnosticKind::InvalidNumber]
-        assert!(matches!(parse.root.children[2].kind, TokenTreeNodeKind::Symbol { .. }));
+        );
+        assert!(matches!(
+            parse.root.children[0].kind,
+            TokenTreeNodeKind::Error { .. }
+        ));
+        assert!(matches!(
+            parse.root.children[1].kind,
+            TokenTreeNodeKind::Number(..)
+        ));
+        assert!(matches!(
+            parse.root.children[2].kind,
+            TokenTreeNodeKind::Symbol { .. }
+        ));
     }
 
     #[test]
     fn numbers_stop_before_non_numeric_sigils() {
         let parse = parse_text("0x1..2");
         assert_eq!(parse.root.children.len(), 3);
-        assert!(matches!(parse.root.children[0].kind, TokenTreeNodeKind::Number(..)));
+        assert!(matches!(
+            parse.root.children[0].kind,
+            TokenTreeNodeKind::Number(..)
+        ));
         assert!(matches!(
             parse.root.children[1].kind,
             TokenTreeNodeKind::Sigil { ref text } if text == ".."
         ));
-        assert!(matches!(parse.root.children[2].kind, TokenTreeNodeKind::Number(..)));
+        assert!(matches!(
+            parse.root.children[2].kind,
+            TokenTreeNodeKind::Number(..)
+        ));
     }
 
     #[test]
@@ -1910,9 +2078,13 @@ mod tests {
         let (rope, parse) = parse_with_rope("{\n  foo\n  [bar]\n}");
         let outer = &parse.root.children[0];
         let bracket = find_list_child(outer, DelimiterKind::Bracket);
-        let range = parse.absolute_range(bracket.id).expect("bracket should have range");
+        let range = parse
+            .absolute_range(bracket.id)
+            .expect("bracket should have range");
         assert_eq!(&parse.text()[range.start..range.end], "[bar]");
-        let (start, end) = parse.absolute_span(&rope, bracket.id).expect("span should exist");
+        let (start, end) = parse
+            .absolute_span(&rope, bracket.id)
+            .expect("span should exist");
         assert_eq!(start.line, 2);
         assert_eq!(start.column, 2);
         assert_eq!(end.line, 2);
@@ -1931,7 +2103,8 @@ mod tests {
 
     #[test]
     fn reparsing_reuses_shifted_subtrees() {
-        let (_rope, first, second, _delta) = reparse_after_edit("{ a b }", RopeEdit::insert(2, "long "));
+        let (_rope, first, second, _delta) =
+            reparse_after_edit("{ a b }", RopeEdit::insert(2, "long "));
         let original_b = first.root.children[0]
             .children
             .iter()
@@ -1962,16 +2135,22 @@ mod tests {
             .find(|node| matches!(&node.kind, TokenTreeNodeKind::Symbol { text } if text == "b"))
             .expect("reparsed tree should contain symbol b");
         assert_eq!(original_b.id, reparsed_b.id);
-        let first_span = first.absolute_span(&rope, original_b.id).expect("first span should exist");
+        let first_span = first
-        let second_span = second.absolute_span(&rope, reparsed_b.id).expect("second span should exist");
+            .absolute_span(&rope, original_b.id)
+            .expect("first span should exist");
+        let second_span = second
+            .absolute_span(&rope, reparsed_b.id)
+            .expect("second span should exist");
         assert_ne!(first_span, second_span);
         assert_eq!(second_span.0.line, 2);
     }
 
     #[test]
     fn reparsing_reuses_unaffected_siblings_when_one_symbol_changes() {
-        let (_rope, first, second, _delta) =
+        let (_rope, first, second, _delta) = reparse_after_edit(
-            reparse_after_edit("{ left right }", RopeEdit::replace(TextRange::new(2, 6), "long"));
+            "{ left right }",
+            RopeEdit::replace(TextRange::new(2, 6), "long"),
+        );
         let first_list = &first.root.children[0];
         let second_list = &second.root.children[0];
         let old_right = first_list.children[1].id;
@@ -1986,8 +2165,14 @@ mod tests {
     fn reparsing_does_not_reuse_node_when_kind_changes() {
         let (_rope, first, second, _delta) =
             reparse_after_edit("foo", RopeEdit::replace(TextRange::new(0, 3), "123"));
-        assert!(matches!(first.root.children[0].kind, TokenTreeNodeKind::Symbol { .. }));
+        assert!(matches!(
-        assert!(matches!(second.root.children[0].kind, TokenTreeNodeKind::Number(..)));
+            first.root.children[0].kind,
+            TokenTreeNodeKind::Symbol { .. }
+        ));
+        assert!(matches!(
+            second.root.children[0].kind,
+            TokenTreeNodeKind::Number(..)
+        ));
         assert_ne!(first.root.children[0].id, second.root.children[0].id);
     }
 
@@ -2046,5 +2231,4 @@ mod tests {
         assert_eq!(seen.len(), 1);
         assert!(seen[0].diagnostics_changed || seen[0].stats.total_nodes > 0);
     }
-
 }

lib/ruin_app/Cargo.toml

@@ -8,9 +8,14 @@ ruin_reactivity = { path = "../reactivity" }
 ruin_runtime = { package = "ruin-runtime", path = "../runtime" }
 ruin_app_proc_macros = { package = "ruin-app-proc-macros", path = "../ruin_app_proc_macros" }
 ruin_ui = { path = "../ui" }
-ruin_ui_platform_wayland = { path = "../ui_platform_wayland" }
 tracing = "0.1"
 
+[target.'cfg(target_os = "linux")'.dependencies]
+ruin_ui_platform_wayland = { path = "../ui_platform_wayland" }
+
+[target.'cfg(target_os = "macos")'.dependencies]
+ruin_ui_platform_macos = { path = "../ui_platform_macos" }
+
 [dev-dependencies]
 tracing-subscriber = { version = "0.3", default-features = false, features = [
     "env-filter",
@@ -47,6 +52,10 @@ path = "example/04_composition_and_context.rs"
 name = "05_async_runtime_io"
 path = "example/05_async_runtime_io.rs"
 
+[[example]]
+name = "06_justify_content"
+path = "example/06_justify_content.rs"
+
 [[example]]
 name = "07_children_and_slots"
 path = "example/07_children_and_slots.rs"

lib/ruin_app/build.rs

@@ -0,0 +1,18 @@
+use std::env;
+use std::path::PathBuf;
+
+fn main() {
+    println!("cargo:rerun-if-changed=macos/Info.plist");
+
+    let target_os = env::var("CARGO_CFG_TARGET_OS").unwrap_or_default();
+    if target_os != "macos" {
+        return;
+    }
+
+    let manifest_dir = PathBuf::from(env::var("CARGO_MANIFEST_DIR").expect("manifest dir"));
+    let plist = manifest_dir.join("macos/Info.plist");
+    let arg = format!("-Wl,-sectcreate,__TEXT,__info_plist,{}", plist.display());
+
+    // Ensure all ruin_app executables/examples opt into Retina rendering.
+    println!("cargo:rustc-link-arg-examples={arg}");
+}

lib/ruin_app/example/00_bootstrap_and_counter.rs

@@ -1,8 +1,17 @@
 use ruin_app::{PartialTextStyle, prelude::*};
 use ruin_ui::{BoxShadow, BoxShadowKind, Point};
+use tracing_subscriber::EnvFilter;
 
 #[ruin_runtime::async_main]
 async fn main() -> ruin_app::Result<()> {
+    let _ = tracing_subscriber::fmt()
+        .with_env_filter(
+            EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new("info")),
+        )
+        .with_target(true)
+        .without_time()
+        .try_init();
+
     let title = "RUIN Counter";
 
     App::new()

lib/ruin_app/example/03_fine_grained_list.rs

@@ -90,21 +90,12 @@ fn TaskBoard() -> impl IntoView {
         }
     });
 
-    let all_label = if matches!(filter.get(), TaskFilter::All) {
+    let all_label = filter_label(matches!(filter.get(), TaskFilter::All), "All");
-        "● All"
+    let open_label = filter_label(matches!(filter.get(), TaskFilter::OpenOnly), "Open");
-    } else {
+    let done_label = filter_label(
-        "○ All"
+        matches!(filter.get(), TaskFilter::CompletedOnly),
-    };
+        "Completed",
-    let open_label = if matches!(filter.get(), TaskFilter::OpenOnly) {
+    );
-        "● Open"
-    } else {
-        "○ Open"
-    };
-    let done_label = if matches!(filter.get(), TaskFilter::CompletedOnly) {
-        "● Completed"
-    } else {
-        "○ Completed"
-    };
     let task_rows = visible_ids.with(|ids| {
         ids.iter()
             .map(|task_id| {
@@ -466,6 +457,14 @@ fn move_task(tasks: &Signal<Vec<Task>>, task_id: u64, direction: MoveDirection)
     });
 }
 
+fn filter_label(active: bool, label: &str) -> String {
+    if active {
+        format!("[x] {label}")
+    } else {
+        format!("[ ] {label}")
+    }
+}
+
 fn seed_tasks() -> Vec<Task> {
     vec![
         Task {

lib/ruin_app/example/06_justify_content.rs

@@ -0,0 +1,194 @@
+//! Visual demonstration of every supported `justify_content` mode.
+//!
+//! The window arranges one labeled cell per mode in a two-column grid. Each
+//! cell is a flex container of the same fixed width with four
+//! identically-sized children, so the only visible difference between cells is
+//! how `justify_content` distributes the leftover space along the main axis.
+
+use ruin_app::prelude::*;
+
+const TRACK_WIDTH: f32 = 360.0;
+const ITEM_SIZE: f32 = 44.0;
+
+#[ruin_runtime::async_main]
+async fn main() -> ruin_app::Result<()> {
+    App::new()
+        .window(
+            Window::new()
+                .title("RUIN justify_content")
+                .app_id("dev.ruin.justify-content")
+                .size(960.0, 620.0),
+        )
+        .mount(view! {
+            JustifyContentGallery() {}
+        })
+        .run()
+        .await
+}
+
+#[component]
+fn JustifyContentGallery() -> impl IntoView {
+    let canvas = Color::rgb(0x10, 0x16, 0x22);
+    let panel = Color::rgb(0x1A, 0x23, 0x33);
+    let accent = Color::rgb(0x71, 0xA7, 0xF7);
+    let text_color = Color::rgb(0xF5, 0xF7, 0xFB);
+    let muted = Color::rgb(0x9A, 0xA9, 0xC2);
+
+    view! {
+        column(gap = 18.0, padding = 24.0, background = canvas) {
+            text(role = TextRole::Heading(1), size = 28.0, weight = FontWeight::Semibold, color = text_color) {
+                "justify_content"
+            }
+            text(color = muted, wrap = TextWrap::Word) {
+                "Each cell below is the same width and contains the same four boxes. The only \
+                 thing that changes between cells is `justify_content`, which controls how the \
+                 leftover space along the main axis is distributed."
+            }
+
+            row(gap = 16.0, align_items = AlignItems::Start) {
+                column(gap = 14.0, flex = 1.0) {
+                    JustifyRow(
+                        label = "Start",
+                        description = "Pack children at the start of the main axis (default).",
+                        justify = JustifyContent::Start,
+                        panel = panel,
+                        accent = accent,
+                        text_color = text_color,
+                        muted = muted,
+                    ) {}
+                    JustifyRow(
+                        label = "End",
+                        description = "Pack children at the end of the main axis.",
+                        justify = JustifyContent::End,
+                        panel = panel,
+                        accent = accent,
+                        text_color = text_color,
+                        muted = muted,
+                    ) {}
+                    JustifyRow(
+                        label = "Center",
+                        description = "Pack children as a group, centered on the main axis.",
+                        justify = JustifyContent::Center,
+                        panel = panel,
+                        accent = accent,
+                        text_color = text_color,
+                        muted = muted,
+                    ) {}
+                }
+                column(gap = 14.0, flex = 1.0) {
+                    JustifyRow(
+                        label = "SpaceBetween",
+                        description = "First child flush with the start, last with the end, equal gaps between.",
+                        justify = JustifyContent::SpaceBetween,
+                        panel = panel,
+                        accent = accent,
+                        text_color = text_color,
+                        muted = muted,
+                    ) {}
+                    JustifyRow(
+                        label = "SpaceAround",
+                        description = "Equal space around each child; end gaps are half the gap between children.",
+                        justify = JustifyContent::SpaceAround,
+                        panel = panel,
+                        accent = accent,
+                        text_color = text_color,
+                        muted = muted,
+                    ) {}
+                    JustifyRow(
+                        label = "SpaceEvenly",
+                        description = "Equal space between children and between children and both edges.",
+                        justify = JustifyContent::SpaceEvenly,
+                        panel = panel,
+                        accent = accent,
+                        text_color = text_color,
+                        muted = muted,
+                    ) {}
+                }
+            }
+        }
+    }
+}
+
+#[component]
+fn JustifyRow(
+    label: &'static str,
+    description: &'static str,
+    justify: JustifyContent,
+    panel: Color,
+    accent: Color,
+    text_color: Color,
+    muted: Color,
+) -> impl IntoView {
+    view! {
+        column(
+            gap = 6.0,
+            padding = 12.0,
+            background = panel,
+            border_radius = 10.0,
+            border = (1.0, accent),
+        ) {
+            row(gap = 10.0, align_items = AlignItems::Center) {
+                text(size = 16.0, weight = FontWeight::Semibold, color = text_color) { label }
+                text(color = muted) { description }
+            }
+            row(
+                width = TRACK_WIDTH,
+                height = ITEM_SIZE + 16.0,
+                padding = 8.0,
+                gap = 8.0,
+                background = Color::rgba(0xFF, 0xFF, 0xFF, 0x10),
+                border_radius = 6.0,
+                align_items = AlignItems::Center,
+                justify_content = justify,
+            ) {
+                JustifyItem(label = "1", accent = accent, text_color = text_color) {}
+                JustifyItem(label = "2", accent = accent, text_color = text_color) {}
+                JustifyItem(label = "3", accent = accent, text_color = text_color) {}
+                JustifyItem(label = "4", accent = accent, text_color = text_color) {}
+            }
+        }
+    }
+}
+
+#[component]
+fn JustifyItem(label: &'static str, accent: Color, text_color: Color) -> impl IntoView {
+    view! {
+        block(
+            width = ITEM_SIZE,
+            height = ITEM_SIZE,
+            background = accent,
+            border_radius = 6.0,
+            align_items = AlignItems::Center,
+        ) {
+            row(
+                flex = 1.0,
+                align_items = AlignItems::Center,
+                justify_content = JustifyContent::Center,
+            ) {
+                text(size = 18.0, weight = FontWeight::Semibold, color = text_color) { label }
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn gallery_renders_all_labels() {
+        let root = JustifyContentGallery::builder().children(());
+        let view = ruin_app::__render_mountable_for_test(&root);
+        let snapshot = ruin_ui::layout_snapshot(1, UiSize::new(960.0, 620.0), view.element());
+
+        for label in ["Start", "End", "Center", "SpaceBetween", "SpaceAround", "SpaceEvenly"] {
+            assert!(
+                snapshot.scene.items.iter().any(|item| matches!(
+                    item,
+                    ruin_ui::DisplayItem::Text(text) if text.text.contains(label)
+                )),
+                "expected `{label}` label to appear in the rendered scene",
+            );
+        }
+    }
+}

lib/ruin_app/example/07_children_and_slots.rs

@@ -259,7 +259,12 @@ fn CardFrame(title: View, toolbar: ChildViews, children: ChildViews) -> impl Int
 }
 
 #[component]
-fn InlineDialog(open: bool, title: View, actions: ChildViews, children: ChildViews) -> impl IntoView {
+fn InlineDialog(
+    open: bool,
+    title: View,
+    actions: ChildViews,
+    children: ChildViews,
+) -> impl IntoView {
     if open {
         let actions_row = view! {
             row(gap = 10.0) {

lib/ruin_app/macos/Info.plist

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
+<plist version="1.0">
+<dict>
+  <key>CFBundleName</key>
+  <string>RUIN</string>
+  <key>CFBundleIdentifier</key>
+  <string>dev.ruin.example</string>
+  <key>CFBundleVersion</key>
+  <string>1</string>
+  <key>CFBundleShortVersionString</key>
+  <string>1.0</string>
+  <key>NSHighResolutionCapable</key>
+  <true/>
+</dict>
+</plist>

lib/ruin_app/src/app.rs

@@ -4,13 +4,18 @@ use std::iter;
 use std::rc::Rc;
 use std::time::Instant;
 
-use ruin_reactivity::effect;
+use ruin_reactivity::{current as current_reactor, effect};
+#[cfg(target_os = "macos")]
+use ruin_runtime::{queue_future, spawn_worker};
 use ruin_ui::{
     Color, Element, InteractionTree, KeyboardEvent, LayoutCache, LayoutSnapshot, PlatformEvent,
     PointerButton, PointerEvent, PointerEventKind, PointerRouter, RoutedPointerEvent,
     RoutedPointerEventKind, TextSystem, UiSize, WindowController, WindowSpec, WindowUpdate,
     layout_snapshot_with_cache,
 };
+#[cfg(target_os = "macos")]
+use ruin_ui_platform_macos::{run_macos_app_event_loop, start_macos_ui};
+#[cfg(target_os = "linux")]
 use ruin_ui_platform_wayland::start_wayland_ui;
 
 use crate::Result;
@@ -24,6 +29,16 @@ use crate::input::{
 };
 use crate::view::View;
 
+#[cfg(target_os = "linux")]
+fn start_platform_ui() -> ruin_ui::UiRuntime {
+    start_wayland_ui()
+}
+
+#[cfg(target_os = "macos")]
+fn start_platform_ui() -> ruin_ui::UiRuntime {
+    start_macos_ui()
+}
+
 #[derive(Clone, Debug)]
 pub struct Window {
     pub(crate) spec: WindowSpec,
@@ -92,8 +107,7 @@ impl App {
     pub fn mount<M: Mountable>(self, root: M) -> MountedApp<M> {
         MountedApp {
             window: self.window,
-            root: Rc::new(root),
+            root,
-            render_state: Rc::new(RenderState::default()),
         }
     }
 }
@@ -139,19 +153,17 @@ impl Mountable for Element {
 
 pub struct MountedApp<M: Mountable> {
     pub(crate) window: Window,
-    pub(crate) root: Rc<M>,
+    pub(crate) root: M,
-    pub(crate) render_state: Rc<RenderState>,
 }
 
 impl<M: Mountable> MountedApp<M> {
-    pub async fn run(self) -> Result<()> {
+    async fn run_with_ui_runtime(
-        let MountedApp {
+        app_window: Window,
-            window: app_window,
+        root: M,
-            root,
+        mut ui: ruin_ui::UiRuntime,
-            render_state,
+    ) -> Result<()> {
-        } = self;
+        let root = Rc::new(root);
-
+        let render_state = Rc::new(RenderState::default());
-        let mut ui = start_wayland_ui();
         let window = ui.create_window(app_window.spec.clone())?;
         let initial_viewport = app_window
             .spec
@@ -159,6 +171,7 @@ impl<M: Mountable> MountedApp<M> {
             .unwrap_or(UiSize::new(960.0, 640.0));
 
         let viewport = ruin_reactivity::cell(initial_viewport);
+        let configure_serial = ruin_reactivity::cell(0_u64);
         let scene_version = StdCell::new(0_u64);
         let text_system = Rc::new(RefCell::new(TextSystem::new()));
         let layout_cache = Rc::new(RefCell::new(LayoutCache::new()));
@@ -177,6 +190,7 @@ impl<M: Mountable> MountedApp<M> {
         let _scene_effect = effect({
             let window = window.clone();
             let viewport = viewport.clone();
+            let configure_serial = configure_serial.clone();
             let text_system = Rc::clone(&text_system);
             let layout_cache = Rc::clone(&layout_cache);
             let interaction_tree = Rc::clone(&interaction_tree);
@@ -193,6 +207,7 @@ impl<M: Mountable> MountedApp<M> {
             let interaction_version = input_state.interaction_version.clone();
             move || {
                 let viewport = viewport.get();
+                let _ = configure_serial.get();
                 let version = scene_version.get().wrapping_add(1);
                 scene_version.set(version);
                 let _ = text_selection.version.get();
@@ -245,7 +260,8 @@ impl<M: Mountable> MountedApp<M> {
                 if window_resizable {
                     let current_min = *last_min_size.borrow();
                     if current_min != Some(desired_min) {
-                        let _ = window.update(WindowUpdate::new().min_inner_size(Some(desired_min)));
+                        let _ =
+                            window.update(WindowUpdate::new().min_inner_size(Some(desired_min)));
                         *last_min_size.borrow_mut() = Some(desired_min);
                     }
                 } else {
@@ -297,6 +313,7 @@ impl<M: Mountable> MountedApp<M> {
                 break;
             };
 
+            let mut should_flush_reactive_work = false;
             for event in iter::once(event).chain(ui.take_pending_events()) {
                 match event {
                     PlatformEvent::Configured {
@@ -310,6 +327,8 @@ impl<M: Mountable> MountedApp<M> {
                             "app received Configured, queuing layout effect"
                         );
                         let _ = viewport.set(configuration.actual_inner_size);
+                        configure_serial.update(|value| *value = value.wrapping_add(1));
+                        should_flush_reactive_work = true;
                     }
                     PlatformEvent::Pointer { window_id, event } if window_id == window.id() => {
                         Self::handle_pointer_event(
@@ -320,6 +339,7 @@ impl<M: Mountable> MountedApp<M> {
                             &mut input_state,
                             event,
                         )?;
+                        should_flush_reactive_work = true;
                     }
                     PlatformEvent::Keyboard { window_id, event } if window_id == window.id() => {
                         Self::handle_keyboard_event(
@@ -329,22 +349,74 @@ impl<M: Mountable> MountedApp<M> {
                             &input_state,
                             event,
                         )?;
+                        should_flush_reactive_work = true;
                     }
                     PlatformEvent::CloseRequested { window_id } if window_id == window.id() => {
+                        tracing::debug!(
+                            target: "ruin_app::lifecycle",
+                            ?window_id,
+                            "app received CloseRequested, issuing open(false)"
+                        );
                         let _ = window.update(WindowUpdate::new().open(false));
                     }
                     PlatformEvent::Closed { window_id } if window_id == window.id() => {
+                        tracing::debug!(
+                            target: "ruin_app::lifecycle",
+                            ?window_id,
+                            "app received Closed, shutting down ui runtime"
+                        );
                         ui.shutdown()?;
                         return Ok(());
                     }
                     _ => {}
                 }
             }
+            if should_flush_reactive_work {
+                current_reactor().flush_now();
+            }
         }
 
         ui.shutdown()?;
         Ok(())
     }
+}
+
+impl<M: Mountable> MountedApp<M> {
+    #[cfg(not(target_os = "macos"))]
+    pub async fn run(self) -> Result<()> {
+        let ui = start_platform_ui();
+        Self::run_with_ui_runtime(self.window, self.root, ui).await
+    }
+
+    #[cfg(target_os = "macos")]
+    pub async fn run(self) -> Result<()>
+    where
+        M: Send + 'static,
+    {
+        let ui = start_platform_ui();
+        let (done_tx, done_rx) = std::sync::mpsc::channel::<std::result::Result<(), String>>();
+        let window = self.window;
+        let root = self.root;
+        let _worker = spawn_worker(
+            move || {
+                queue_future(async move {
+                    let result = Self::run_with_ui_runtime(window, root, ui)
+                        .await
+                        .map_err(|err| err.to_string());
+                    let _ = done_tx.send(result);
+                });
+            },
+            || {},
+        );
+
+        run_macos_app_event_loop();
+
+        match done_rx.recv() {
+            Ok(Ok(())) => Ok(()),
+            Ok(Err(err)) => Err(err.into()),
+            Err(_) => Err("ui worker terminated before completion".into()),
+        }
+    }
 
     pub(crate) fn handle_pointer_event(
         window: &WindowController,
@@ -508,7 +580,10 @@ impl<M: Mountable> MountedApp<M> {
     }
 
     fn interaction_ids(targets: &[ruin_ui::HitTarget]) -> Vec<ruin_ui::ElementId> {
-        targets.iter().filter_map(|target| target.element_id).collect()
+        targets
+            .iter()
+            .filter_map(|target| target.element_id)
+            .collect()
     }
 
     fn update_interaction_state(
@@ -518,8 +593,14 @@ impl<M: Mountable> MountedApp<M> {
     ) -> bool {
         let previous_hovered = input_state.hovered_elements.get();
         let previous_pressed = input_state.pressed_elements.get();
-        let hovered_changed = input_state.hovered_elements.set(hovered_ids.clone()).is_some();
+        let hovered_changed = input_state
-        let pressed_changed = input_state.pressed_elements.set(pressed_ids.clone()).is_some();
+            .hovered_elements
+            .set(hovered_ids.clone())
+            .is_some();
+        let pressed_changed = input_state
+            .pressed_elements
+            .set(pressed_ids.clone())
+            .is_some();
         if hovered_changed || pressed_changed {
             tracing::trace!(
                 target: "ruin_app::interaction",

lib/ruin_app/src/context.rs

@@ -99,10 +99,7 @@ pub(crate) fn render_with_context_and_interaction(
     RenderOutput { view, side_effects }
 }
 
-pub(crate) fn with_render_context(
+pub(crate) fn with_render_context(context: RenderContext, render: impl FnOnce() -> View) -> View {
-    context: RenderContext,
-    render: impl FnOnce() -> View,
-) -> View {
     CURRENT_RENDER_CONTEXT.with(|slot| {
         let previous = slot.replace(Some(context.clone()));
 

lib/ruin_app/src/hooks.rs

@@ -1,5 +1,5 @@
-use std::any::type_name;
 use std::any::TypeId;
+use std::any::type_name;
 use std::cell::Cell as StdCell;
 use std::future::Future;
 use std::marker::PhantomData;
@@ -9,8 +9,8 @@ use ruin_ui::{ElementId, InteractionTree, KeyboardEvent, KeyboardEventKind, Keyb
 
 use crate::ContextKey;
 use crate::context::{
-    ContextEntry, MemoSlot, ResourceSlot, with_hook_slot,
+    ContextEntry, MemoSlot, ResourceSlot, with_hook_slot, with_render_context,
-    with_render_context, with_render_context_state,
+    with_render_context_state,
 };
 use crate::input::ShortcutBinding;
 
@@ -114,7 +114,10 @@ pub fn use_context<C: ContextKey>() -> C::Value {
     })
 }
 
-pub fn provide<C: ContextKey>(value: C::Value, render: impl FnOnce() -> crate::view::View) -> crate::view::View {
+pub fn provide<C: ContextKey>(
+    value: C::Value,
+    render: impl FnOnce() -> crate::view::View,
+) -> crate::view::View {
     with_render_context_state(|context| {
         let mut context_entries = (*context.context_entries).clone();
         context_entries.push(ContextEntry::new::<C>(value));

lib/ruin_app/src/input.rs

@@ -3,9 +3,8 @@ use std::collections::HashMap;
 use std::rc::Rc;
 
 use ruin_ui::{
-    CursorIcon, DisplayItem, ElementId, HitTarget, InteractionTree, KeyboardEvent,
+    CursorIcon, DisplayItem, ElementId, HitTarget, InteractionTree, KeyboardEvent, PointerButton,
-    PointerButton, PointerEvent, Quad, RoutedPointerEvent,
+    PointerEvent, Quad, RoutedPointerEvent, RoutedPointerEventKind, WindowController,
-    RoutedPointerEventKind, WindowController,
 };
 
 use crate::hooks::{Shortcut, ShortcutScope, Signal};
@@ -76,8 +75,7 @@ impl EventBindings {
         event: &KeyboardEvent,
         interaction_tree: &InteractionTree,
     ) {
-        let Some(handler) =
+        let Some(handler) = key_handler_for_focus(&self.on_key, focused_element, interaction_tree)
-            key_handler_for_focus(&self.on_key, focused_element, interaction_tree)
         else {
             return;
         };
@@ -200,20 +198,29 @@ pub(crate) fn sync_primary_selection(
     interaction_tree: &InteractionTree,
     selection: Option<TextSelection>,
 ) -> crate::Result<()> {
-    let Some(selection) = selection else {
+    #[cfg(not(target_os = "linux"))]
-        window.set_primary_selection_text(String::new())?;
+    {
-        return Ok(());
+        let _ = (window, interaction_tree, selection);
-    };
+        Ok(())
+    }
 
-    let Some(text) = interaction_tree.text_for_element(selection.element_id) else {
+    #[cfg(target_os = "linux")]
-        return Ok(());
+    {
-    };
+        let Some(selection) = selection else {
-    let copied = text
+            window.set_primary_selection_text(String::new())?;
-        .selected_text(selection.anchor, selection.focus)
+            return Ok(());
-        .unwrap_or_default()
+        };
-        .to_owned();
+
-    window.set_primary_selection_text(copied)?;
+        let Some(text) = interaction_tree.text_for_element(selection.element_id) else {
-    Ok(())
+            return Ok(());
+        };
+        let copied = text
+            .selected_text(selection.anchor, selection.focus)
+            .unwrap_or_default()
+            .to_owned();
+        window.set_primary_selection_text(copied)?;
+        Ok(())
+    }
 }
 
 pub(crate) fn scroll_handler_for_event<'a>(
@@ -325,7 +332,11 @@ pub(crate) fn build_focused_ancestor_chain(
 
 // View helper methods for attaching handlers — used by primitives
 impl View {
-    pub(crate) fn with_press_handler(mut self, element_id: ElementId, handler: PressHandler) -> Self {
+    pub(crate) fn with_press_handler(
+        mut self,
+        element_id: ElementId,
+        handler: PressHandler,
+    ) -> Self {
         self.bindings.on_press.insert(element_id, handler);
         self
     }
@@ -339,11 +350,7 @@ impl View {
         self
     }
 
-    pub(crate) fn with_key_handler(
+    pub(crate) fn with_key_handler(mut self, element_id: ElementId, handler: KeyHandler) -> Self {
-        mut self,
-        element_id: ElementId,
-        handler: KeyHandler,
-    ) -> Self {
         self.bindings.on_key.insert(element_id, handler);
         self
     }

lib/ruin_app/src/lib.rs

@@ -9,8 +9,8 @@ use std::error::Error;
 
 pub mod app;
 pub mod colors;
-pub mod converters;
 mod context;
+pub mod converters;
 mod hooks;
 mod input;
 pub mod primitives;
@@ -20,22 +20,22 @@ pub mod view;
 
 // Re-export public items from each module.
 
-pub use app::{App, Component, ContextKey, MountedApp, Mountable, Window, __render_mountable_for_test};
+pub use app::{
+    __render_mountable_for_test, App, Component, ContextKey, Mountable, MountedApp, Window,
+};
 pub use converters::{IntoBorder, IntoEdges, IntoShadow};
 pub use hooks::{
-    BlockWidget, FocusScope, InteractionState, Key, Memo, Resource, ResourceState,
+    BlockWidget, FocusScope, InteractionState, Key, Memo, Resource, ResourceState, ScrollBoxWidget,
-    ScrollBoxWidget, Shortcut, ShortcutScope, Signal, WidgetRef, provide, use_context,
+    Shortcut, ShortcutScope, Signal, WidgetRef, provide, use_context, use_effect,
-    use_effect, use_interaction_state, use_memo, use_resource, use_shortcut,
+    use_interaction_state, use_memo, use_resource, use_shortcut, use_shortcut_with_context,
-    use_shortcut_with_context, use_signal, use_widget_ref, use_window_title,
+    use_signal, use_widget_ref, use_window_title,
 };
 pub use primitives::{
     ButtonBuilder, ContainerBuilder, ContainerProps, FontWeight, ScrollBoxBuilder, TextBuilder,
     TextRole, block, button, column, row, scroll_box, text,
 };
 pub use text_style::PartialTextStyle;
-pub use view::{
+pub use view::{ChildViews, Children, IntoView, LazyChildren, TextChildren, TextValue, View};
-    ChildViews, Children, IntoView, LazyChildren, TextChildren, TextValue, View,
-};
 
 // Bare string literals as container children produce a text element with context-aware styling.
 // These impls live here (not in view.rs) so they can call primitives::text().
@@ -58,10 +58,11 @@ pub use ruin_app_proc_macros::{component, context_provider, view};
 pub type Result<T> = std::result::Result<T, Box<dyn Error>>;
 
 pub mod prelude {
+    pub use crate::PartialTextStyle;
     pub use crate::{
         App, BlockWidget, ButtonBuilder, ChildViews, Children, Component, ContainerBuilder,
-        ContextKey, FocusScope, FontWeight, InteractionState, IntoBorder, IntoEdges, IntoView,
+        ContextKey, FocusScope, FontWeight, InteractionState, IntoBorder, IntoEdges, IntoView, Key,
-        Key, Memo, Mountable, Pending, Ready, Resource, ResourceState, Result, ScrollBoxBuilder,
+        Memo, Mountable, Pending, Ready, Resource, ResourceState, Result, ScrollBoxBuilder,
         ScrollBoxWidget, Shortcut, ShortcutScope, Signal, TextBuilder, TextChildren, TextRole,
         TextValue, View, WidgetRef, Window, block, button, colors, column, component,
         context_provider, provide, row, scroll_box, surfaces, text, use_context, use_effect,
@@ -70,10 +71,9 @@ pub mod prelude {
     };
     pub use ruin_ui::{
         AlignItems, Border, Color, CursorIcon, Edges, Element, ElementId, InteractionTree,
-        PointerButton, PointerEventKind, RoutedPointerEvent, RoutedPointerEventKind,
+        JustifyContent, PointerButton, PointerEventKind, RoutedPointerEvent,
-        ScrollbarStyle, TextFontFamily, TextStyle, TextWrap, UiSize,
+        RoutedPointerEventKind, ScrollbarStyle, TextFontFamily, TextStyle, TextWrap, UiSize,
     };
-    pub use crate::PartialTextStyle;
 }
 
 #[cfg(test)]
@@ -201,7 +201,10 @@ mod tests {
             }
         });
 
-        let widget_ref = widget_ref_slot.borrow().clone().expect("widget ref should be set");
+        let widget_ref = widget_ref_slot
+            .borrow()
+            .clone()
+            .expect("widget ref should be set");
         let element_id = widget_ref
             .element_id()
             .expect("widget ref should have an element id after render");
@@ -216,7 +219,10 @@ mod tests {
                 let pressed = Rc::clone(&pressed);
                 let widget_ref_slot = Rc::clone(&widget_ref_slot);
                 move || {
-                    let widget_ref = widget_ref_slot.borrow().clone().expect("widget ref should persist");
+                    let widget_ref = widget_ref_slot
+                        .borrow()
+                        .clone()
+                        .expect("widget ref should persist");
                     *hovered.borrow_mut() = Some(use_interaction_state(widget_ref.clone()).hovered);
                     *pressed.borrow_mut() = Some(use_interaction_state(widget_ref.clone()).pressed);
                     block().widget_ref(widget_ref).children(())
@@ -292,7 +298,10 @@ mod tests {
 
     #[test]
     fn scroll_box_arrow_keys_work_after_clicking_text_content() {
-        use ruin_ui::{KeyboardEvent, KeyboardEventKind, KeyboardKey, PointerEvent, PointerEventKind, PointerButton};
+        use ruin_ui::{
+            KeyboardEvent, KeyboardEventKind, KeyboardKey, PointerButton, PointerEvent,
+            PointerEventKind,
+        };
 
         let offset_slot = Rc::new(RefCell::new(None::<Signal<f32>>));
         let render = render_with_context(Rc::new(RenderState::default()), {
@@ -428,7 +437,7 @@ mod tests {
 
     #[test]
     fn live_input_path_scrolls_a_scroll_box_rendered_inside_a_branch() {
-        use ruin_ui::{PointerEvent, PointerEventKind, PointerButton};
+        use ruin_ui::{PointerButton, PointerEvent, PointerEventKind};
 
         let offset_slot = Rc::new(RefCell::new(None::<Signal<f32>>));
         let render = render_with_context(Rc::new(RenderState::default()), {
@@ -466,8 +475,11 @@ mod tests {
             .borrow()
             .clone()
             .expect("scroll signal should have been captured");
-        let snapshot =
+        let snapshot = ruin_ui::layout_snapshot(
-            ruin_ui::layout_snapshot(1, ruin_ui::UiSize::new(1080.0, 760.0), render.view.element());
+            1,
+            ruin_ui::UiSize::new(1080.0, 760.0),
+            render.view.element(),
+        );
         let interaction_tree = RefCell::new(Some(snapshot.interaction_tree.clone()));
         let bindings = RefCell::new(render.view.bindings.clone());
         let mut pointer_router = ruin_ui::PointerRouter::new();
@@ -511,7 +523,7 @@ mod tests {
 
     #[test]
     fn scroll_box_stays_interactive_when_it_appears_on_a_later_render() {
-        use ruin_ui::{PointerEvent, PointerEventKind, PointerButton};
+        use ruin_ui::{PointerButton, PointerEvent, PointerEventKind};
 
         let state = Rc::new(RenderState::default());
         let ready_slot = Rc::new(RefCell::new(None::<Signal<bool>>));
@@ -571,8 +583,11 @@ mod tests {
         let _ = ready.set(true);
 
         let render = render_once(state, ready_slot, Rc::clone(&offset_slot));
-        let snapshot =
+        let snapshot = ruin_ui::layout_snapshot(
-            ruin_ui::layout_snapshot(1, ruin_ui::UiSize::new(1080.0, 760.0), render.view.element());
+            1,
+            ruin_ui::UiSize::new(1080.0, 760.0),
+            render.view.element(),
+        );
         let interaction_tree = RefCell::new(Some(snapshot.interaction_tree.clone()));
         let bindings = RefCell::new(render.view.bindings.clone());
         let mut pointer_router = ruin_ui::PointerRouter::new();
@@ -646,8 +661,11 @@ mod tests {
             .borrow()
             .clone()
             .expect("scroll signal should have been captured");
-        let snapshot =
+        let snapshot = ruin_ui::layout_snapshot(
-            ruin_ui::layout_snapshot(1, ruin_ui::UiSize::new(1080.0, 760.0), render.view.element());
+            1,
+            ruin_ui::UiSize::new(1080.0, 760.0),
+            render.view.element(),
+        );
         let interaction_tree = RefCell::new(Some(snapshot.interaction_tree.clone()));
         let bindings = RefCell::new(render.view.bindings.clone());
         let mut pointer_router = ruin_ui::PointerRouter::new();

lib/ruin_app/src/primitives/button.rs

@@ -5,9 +5,9 @@ use ruin_ui::{CursorIcon, Edges, Element, RoutedPointerEvent};
 use crate::context::allocate_element_id;
 use crate::input::PressHandler;
 use crate::primitives::ContainerProps;
+use crate::surfaces;
 use crate::text_style::{pop_text_style, push_text_style};
 use crate::view::{Children, View};
-use crate::surfaces;
 
 pub struct ButtonBuilder {
     pub(crate) props: ContainerProps,

lib/ruin_app/src/primitives/container.rs

@@ -1,4 +1,4 @@
-use ruin_ui::{AlignItems, Color, Element, ElementId};
+use ruin_ui::{AlignItems, Color, Element, ElementId, JustifyContent};
 
 use crate::context::allocate_element_id;
 use crate::converters::{IntoBorder, IntoEdges, IntoShadow};
@@ -92,6 +92,11 @@ impl ContainerProps {
         self
     }
 
+    pub fn justify_content(mut self, justify: JustifyContent) -> Self {
+        self.element = self.element.justify_content(justify);
+        self
+    }
+
     pub fn shadow(mut self, shadow: impl IntoShadow) -> Self {
         self.element = self.element.shadow(shadow.into_shadow());
         self

lib/ruin_app/src/primitives/mod.rs

@@ -53,6 +53,10 @@ macro_rules! impl_props_methods {
             self.props = self.props.align_self(align);
             self
         }
+        pub fn justify_content(mut self, justify: ruin_ui::JustifyContent) -> Self {
+            self.props = self.props.justify_content(justify);
+            self
+        }
         pub fn widget_ref<T>(mut self, widget_ref: $crate::hooks::WidgetRef<T>) -> Self {
             self.props = self.props.widget_ref(widget_ref);
             self

lib/ruin_app/src/text_style.rs

@@ -56,6 +56,8 @@ pub(crate) fn current_text_style() -> PartialTextStyle {
         stack
             .borrow()
             .iter()
-            .fold(PartialTextStyle::default(), |acc, layer| acc.merge_over(layer))
+            .fold(PartialTextStyle::default(), |acc, layer| {
+                acc.merge_over(layer)
+            })
     })
 }

lib/ruin_app/src/view.rs

@@ -86,7 +86,6 @@ impl Children for () {
     }
 }
 
-
 impl<T: IntoView> Children for T {
     fn into_views(self) -> Vec<View> {
         vec![self.into_view()]

lib/ruin_app_proc_macros/src/lib.rs

@@ -60,10 +60,7 @@ fn expand_component(mut function: ItemFn) -> Result<proc_macro2::TokenStream> {
         Some(prop) if prop.ident == "children" => {
             let prop = inputs.pop().expect("last input should exist");
             let kind = parse_children_contract_kind(&prop.ty)?;
-            Some(ChildContract {
+            Some(ChildContract { ty: prop.ty, kind })
-                ty: prop.ty,
-                kind,
-            })
         }
         _ => None,
     };
@@ -87,7 +84,8 @@ fn expand_component(mut function: ItemFn) -> Result<proc_macro2::TokenStream> {
             }
             Some(contract) => {
                 let child_arg_ty = child_builder_arg_type_tokens(contract.kind);
-                let child_value = wrap_special_value_tokens(contract.kind, &format_ident!("children"));
+                let child_value =
+                    wrap_special_value_tokens(contract.kind, &format_ident!("children"));
                 let child_field_ident = child_field_ident
                     .as_ref()
                     .expect("child field ident should exist");
@@ -574,10 +572,7 @@ fn child_builder_arg_type_tokens(kind: SpecialValueKind) -> proc_macro2::TokenSt
     }
 }
 
-fn wrap_special_value_tokens(
+fn wrap_special_value_tokens(kind: SpecialValueKind, ident: &Ident) -> proc_macro2::TokenStream {
-    kind: SpecialValueKind,
-    ident: &Ident,
-) -> proc_macro2::TokenStream {
     match kind {
         SpecialValueKind::Plain => quote! { #ident },
         SpecialValueKind::ChildViews => quote! { ::ruin_app::ChildViews::from_children(#ident) },

lib/runtime/src/channel/mpsc.rs

@@ -7,7 +7,7 @@ use std::sync::{Arc, Mutex};
 use std::task::{Context, Poll};
 
 use crate::op::completion::{CompletionFuture, CompletionHandle};
-use crate::sys::linux::channel::runtime_waiter;
+use crate::sys::current::channel::runtime_waiter;
 
 /// Creates a bounded channel with room for at most `capacity` queued messages.
 ///

lib/runtime/src/channel/oneshot.rs

@@ -6,7 +6,7 @@ use std::sync::{Arc, Mutex};
 use std::task::{Context, Poll};
 
 use crate::op::completion::{CompletionFuture, CompletionHandle};
-use crate::sys::linux::channel::runtime_waiter;
+use crate::sys::current::channel::runtime_waiter;
 
 /// Creates a single-use channel for transferring one value from a [`Sender`] to a [`Receiver`].
 ///

lib/runtime/src/fd.rs

@@ -3,44 +3,9 @@
 use std::io;
 use std::os::fd::RawFd;
 
-use crate::op::completion::completion_for_current_thread;
-use crate::platform::linux_x86_64::runtime::with_current_driver;
-use crate::platform::linux_x86_64::uring::{IORING_OP_POLL_ADD, IoUringCqe};
-
 /// Waits until `fd` becomes readable or reports an error/hangup condition.
 pub async fn wait_readable(fd: RawFd) -> io::Result<()> {
-    submit_poll(fd, libc::POLLIN | libc::POLLERR | libc::POLLHUP).await
+    crate::sys::current::fd::wait_readable(fd).await
-}
-
-async fn submit_poll(fd: RawFd, mask: i16) -> io::Result<()> {
-    let (future, handle) = completion_for_current_thread::<io::Result<()>>();
-    let callback_handle = handle.clone();
-    let token = with_current_driver(|driver| {
-        driver.submit_operation(
-            move |sqe| {
-                sqe.opcode = IORING_OP_POLL_ADD;
-                sqe.fd = fd;
-                sqe.len = 0;
-                sqe.op_flags = mask as u32;
-            },
-            move |cqe| {
-                callback_handle.complete(cqe_to_result(cqe));
-            },
-        )
-    })?;
-
-    handle.set_cancel(move || {
-        let _ = with_current_driver(|driver| driver.cancel_operation(token));
-    });
-
-    future.await
-}
-
-fn cqe_to_result(cqe: IoUringCqe) -> io::Result<()> {
-    if cqe.res < 0 {
-        return Err(io::Error::from_raw_os_error(-cqe.res));
-    }
-    Ok(())
 }
 
 #[cfg(test)]
@@ -53,8 +18,8 @@ mod tests {
     #[test]
     fn wait_readable_resolves_for_pipe() {
         let mut fds = [0; 2];
-        let result = unsafe { libc::pipe2(fds.as_mut_ptr(), libc::O_CLOEXEC | libc::O_NONBLOCK) };
+        let result = unsafe { libc::pipe(fds.as_mut_ptr()) };
-        assert_eq!(result, 0, "pipe2 should succeed");
+        assert_eq!(result, 0, "pipe should succeed");
         let read_fd = fds[0];
         let write_fd = fds[1];
 

lib/runtime/src/fs.rs

@@ -19,7 +19,7 @@ use crate::op::fs::{
     FileType as RawFileType, FsOp, MetadataTarget, OpenOptions as OpOpenOptions,
     RawDirEntry as OpDirEntry, RawMetadata,
 };
-use crate::sys::linux::fs as sys_fs;
+use crate::sys::current::fs as sys_fs;
 
 struct FileInner {
     fd: OwnedFd,

lib/runtime/src/lib.rs

@@ -1,7 +1,7 @@
 //! Runtime, driver, async I/O, and channel primitives for RUIN.
 //!
 //! The crate is centered around a single-threaded event loop with explicit worker threads,
-//! JavaScript-style microtask/macrotask scheduling, and Linux `io_uring`-backed I/O.
+//! JavaScript-style microtask/macrotask scheduling and platform-specific async I/O backends.
 //!
 //! Most users will start with:
 //!
@@ -11,17 +11,22 @@
 //!
 //! # Platform support
 //!
-//! `ruin-runtime` currently targets Linux on `x86_64`.
+//! `ruin-runtime` currently targets:
+//! - Linux `x86_64`
+//! - macOS `aarch64`
 //!
 //! RUIN runtime foundations.
 //!
-//! This crate provides a Linux x86_64 runtime substrate: the mesh allocator, the driver, and a
+//! This crate provides a platform runtime substrate with a single-threaded runtime loop and
-//! single-threaded runtime loop with worker-thread task forwarding.
+//! worker-thread task forwarding.
 
 #![feature(thread_local)]
 
-#[cfg(not(all(target_os = "linux", target_arch = "x86_64")))]
+#[cfg(not(any(
-compile_error!("ruin-runtime currently supports only Linux x86_64.");
+    all(target_os = "linux", target_arch = "x86_64"),
+    all(target_os = "macos", target_arch = "aarch64")
+)))]
+compile_error!("ruin-runtime currently supports Linux x86_64 and macOS aarch64.");
 
 extern crate alloc;
 
@@ -60,11 +65,24 @@ pub use ruin_runtime_proc_macros::async_main;
 /// thread before calling [`run`].
 pub use ruin_runtime_proc_macros::main;
 
-/// Driver primitives re-exported from the Linux x86_64 backend.
+/// Driver primitives re-exported from the active backend.
-#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
+#[cfg(any(
-pub use platform::linux_x86_64::driver::{
+    all(target_os = "linux", target_arch = "x86_64"),
+    all(target_os = "macos", target_arch = "aarch64")
+))]
+pub use platform::current::driver::{
     Driver, ReadyEvents, ThreadNotifier, create, create_driver, monotonic_now,
 };
+/// Runtime/event-loop primitives re-exported from the active backend.
+#[cfg(any(
+    all(target_os = "linux", target_arch = "x86_64"),
+    all(target_os = "macos", target_arch = "aarch64")
+))]
+pub use platform::current::runtime::{
+    IntervalHandle, JoinHandle, ThreadHandle, TimeoutHandle, WorkerHandle, clear_interval,
+    clear_timeout, current_thread_handle, queue_future, queue_microtask, queue_task, run,
+    run_ready_tasks, run_until_stalled, set_interval, set_timeout, spawn_worker, yield_now,
+};
 /// Public mesh-allocator surface re-exported from the Linux x86_64 backend.
 #[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 pub use platform::linux_x86_64::mesh_alloc::{
@@ -81,22 +99,17 @@ pub use platform::linux_x86_64::mesh_alloc::{
 /// Additional allocator helpers re-exported from the Linux x86_64 backend.
 #[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 pub use platform::linux_x86_64::mesh_alloc::{FreelistId, bitmaps_meshable};
-/// Runtime/event-loop primitives re-exported from the Linux x86_64 backend.
-#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
-pub use platform::linux_x86_64::runtime::{
-    IntervalHandle, JoinHandle, ThreadHandle, TimeoutHandle, WorkerHandle, clear_interval,
-    clear_timeout, current_thread_handle, queue_future, queue_microtask, queue_task, run,
-    set_interval, set_timeout, spawn_worker, yield_now,
-};
 
 /// Returns the default global mesh allocator configuration for this crate.
 ///
 /// This is useful when embedding the allocator in a `#[global_allocator]` static.
+#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 pub const fn default_global_allocator() -> GlobalMeshAllocator {
     GlobalMeshAllocator::with_default_config()
 }
 
 #[cfg(test)]
+#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 mod tests {
     use super::{MeshAllocator, page_size};
 

lib/runtime/src/net.rs

@@ -73,10 +73,10 @@ impl TcpStream {
     where
         A: ToSocketAddrs + Send + 'static,
     {
-        let addrs = crate::sys::linux::net::resolve_addrs(addr).await?;
+        let addrs = crate::sys::current::net::resolve_addrs(addr).await?;
         let mut last_error = None;
         for addr in addrs {
-            match crate::sys::linux::net::connect_stream(addr).await {
+            match crate::sys::current::net::connect_stream(addr).await {
                 Ok(fd) => return Ok(Self::from_owned_fd(fd)),
                 Err(error) => last_error = Some(error),
             }
@@ -93,7 +93,7 @@ impl TcpStream {
     /// Connects to `addr`, failing if the deadline elapses first.
     pub async fn connect_timeout(addr: &SocketAddr, timeout: Duration) -> io::Result<Self> {
         validate_timeout(timeout)?;
-        crate::sys::linux::net::connect_stream_timeout(*addr, timeout)
+        crate::sys::current::net::connect_stream_timeout(*addr, timeout)
             .await
             .map(Self::from_owned_fd)
     }
@@ -102,10 +102,10 @@ impl TcpStream {
     pub async fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         let data = match self.read_timeout_value() {
             Some(timeout) => {
-                crate::sys::linux::net::recv_timeout(self.raw_fd(), buf.len(), 0, timeout).await?
+                crate::sys::current::net::recv_timeout(self.raw_fd(), buf.len(), 0, timeout).await?
             }
             None => {
-                crate::sys::linux::net::recv(NetOp::Recv {
+                crate::sys::current::net::recv(NetOp::Recv {
                     fd: self.raw_fd(),
                     len: buf.len(),
                     flags: 0,
@@ -137,10 +137,11 @@ impl TcpStream {
     pub async fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         match self.write_timeout_value() {
             Some(timeout) => {
-                crate::sys::linux::net::send_timeout(self.raw_fd(), buf.to_vec(), 0, timeout).await
+                crate::sys::current::net::send_timeout(self.raw_fd(), buf.to_vec(), 0, timeout)
+                    .await
             }
             None => {
-                crate::sys::linux::net::send(NetOp::Send {
+                crate::sys::current::net::send(NetOp::Send {
                     fd: self.raw_fd(),
                     data: buf.to_vec(),
                     flags: 0,
@@ -167,7 +168,7 @@ impl TcpStream {
 
     /// Shuts down the read, write, or both halves of the connection.
     pub async fn shutdown(&self, how: Shutdown) -> io::Result<()> {
-        crate::sys::linux::net::shutdown(NetOp::Shutdown {
+        crate::sys::current::net::shutdown(NetOp::Shutdown {
             fd: self.raw_fd(),
             how,
         })
@@ -176,39 +177,39 @@ impl TcpStream {
 
     /// Duplicates the underlying stream socket.
     pub async fn try_clone(&self) -> io::Result<Self> {
-        crate::sys::linux::net::duplicate(self.raw_fd())
+        crate::sys::current::net::duplicate(self.raw_fd())
             .await
             .map(Self::from_owned_fd)
     }
 
     /// Returns the local socket address of this stream.
     pub fn local_addr(&self) -> io::Result<SocketAddr> {
-        crate::sys::linux::net::local_addr(self.raw_fd())
+        crate::sys::current::net::local_addr(self.raw_fd())
     }
 
     /// Returns the remote peer address of this stream.
     pub fn peer_addr(&self) -> io::Result<SocketAddr> {
-        crate::sys::linux::net::peer_addr(self.raw_fd())
+        crate::sys::current::net::peer_addr(self.raw_fd())
     }
 
     /// Reads the current `TCP_NODELAY` setting.
     pub fn nodelay(&self) -> io::Result<bool> {
-        crate::sys::linux::net::nodelay(self.raw_fd())
+        crate::sys::current::net::nodelay(self.raw_fd())
     }
 
     /// Enables or disables `TCP_NODELAY`.
     pub fn set_nodelay(&self, enabled: bool) -> io::Result<()> {
-        crate::sys::linux::net::set_nodelay(self.raw_fd(), enabled)
+        crate::sys::current::net::set_nodelay(self.raw_fd(), enabled)
     }
 
     /// Reads the socket's IP time-to-live value.
     pub fn ttl(&self) -> io::Result<u32> {
-        crate::sys::linux::net::ttl(self.raw_fd())
+        crate::sys::current::net::ttl(self.raw_fd())
     }
 
     /// Sets the socket's IP time-to-live value.
     pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
-        crate::sys::linux::net::set_ttl(self.raw_fd(), ttl)
+        crate::sys::current::net::set_ttl(self.raw_fd(), ttl)
     }
 
     /// Returns the read timeout used by async read operations on this handle.
@@ -270,10 +271,10 @@ impl TcpListener {
     where
         A: ToSocketAddrs + Send + 'static,
     {
-        let addrs = crate::sys::linux::net::resolve_addrs(addr).await?;
+        let addrs = crate::sys::current::net::resolve_addrs(addr).await?;
         let mut last_error = None;
         for addr in addrs {
-            match crate::sys::linux::net::bind_listener(addr, None).await {
+            match crate::sys::current::net::bind_listener(addr, None).await {
                 Ok(fd) => return Ok(Self::from_owned_fd(fd)),
                 Err(error) => last_error = Some(error),
             }
@@ -289,7 +290,8 @@ impl TcpListener {
 
     /// Accepts an incoming connection.
     pub async fn accept(&self) -> io::Result<(TcpStream, SocketAddr)> {
-        let accepted = crate::sys::linux::net::accept(NetOp::Accept { fd: self.raw_fd() }).await?;
+        let accepted =
+            crate::sys::current::net::accept(NetOp::Accept { fd: self.raw_fd() }).await?;
 
         let stream = TcpStream::from_owned_fd(unsafe { OwnedFd::from_raw_fd(accepted.fd) });
         Ok((stream, accepted.peer_addr))
@@ -297,17 +299,17 @@ impl TcpListener {
 
     /// Returns the local socket address of this listener.
     pub fn local_addr(&self) -> io::Result<SocketAddr> {
-        crate::sys::linux::net::local_addr(self.raw_fd())
+        crate::sys::current::net::local_addr(self.raw_fd())
     }
 
     /// Reads the listener socket's IP time-to-live value.
     pub fn ttl(&self) -> io::Result<u32> {
-        crate::sys::linux::net::ttl(self.raw_fd())
+        crate::sys::current::net::ttl(self.raw_fd())
     }
 
     /// Sets the listener socket's IP time-to-live value.
     pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
-        crate::sys::linux::net::set_ttl(self.raw_fd(), ttl)
+        crate::sys::current::net::set_ttl(self.raw_fd(), ttl)
     }
 
     fn from_owned_fd(fd: OwnedFd) -> Self {
@@ -327,10 +329,10 @@ impl UdpSocket {
     where
         A: ToSocketAddrs + Send + 'static,
     {
-        let addrs = crate::sys::linux::net::resolve_addrs(addr).await?;
+        let addrs = crate::sys::current::net::resolve_addrs(addr).await?;
         let mut last_error = None;
         for addr in addrs {
-            match crate::sys::linux::net::bind_datagram(addr).await {
+            match crate::sys::current::net::bind_datagram(addr).await {
                 Ok(fd) => return Ok(Self::from_owned_fd(fd)),
                 Err(error) => last_error = Some(error),
             }
@@ -352,10 +354,10 @@ impl UdpSocket {
     where
         A: ToSocketAddrs + Send + 'static,
     {
-        let addrs = crate::sys::linux::net::resolve_addrs(addr).await?;
+        let addrs = crate::sys::current::net::resolve_addrs(addr).await?;
         let mut last_error = None;
         for addr in addrs {
-            match crate::sys::linux::net::connect(NetOp::Connect {
+            match crate::sys::current::net::connect(NetOp::Connect {
                 fd: self.raw_fd(),
                 addr,
             })
@@ -378,10 +380,11 @@ impl UdpSocket {
     pub async fn send(&self, buf: &[u8]) -> io::Result<usize> {
         match self.write_timeout_value() {
             Some(timeout) => {
-                crate::sys::linux::net::send_timeout(self.raw_fd(), buf.to_vec(), 0, timeout).await
+                crate::sys::current::net::send_timeout(self.raw_fd(), buf.to_vec(), 0, timeout)
+                    .await
             }
             None => {
-                crate::sys::linux::net::send(NetOp::Send {
+                crate::sys::current::net::send(NetOp::Send {
                     fd: self.raw_fd(),
                     data: buf.to_vec(),
                     flags: 0,
@@ -395,10 +398,10 @@ impl UdpSocket {
     pub async fn recv(&self, buf: &mut [u8]) -> io::Result<usize> {
         let data = match self.read_timeout_value() {
             Some(timeout) => {
-                crate::sys::linux::net::recv_timeout(self.raw_fd(), buf.len(), 0, timeout).await?
+                crate::sys::current::net::recv_timeout(self.raw_fd(), buf.len(), 0, timeout).await?
             }
             None => {
-                crate::sys::linux::net::recv(NetOp::Recv {
+                crate::sys::current::net::recv(NetOp::Recv {
                     fd: self.raw_fd(),
                     len: buf.len(),
                     flags: 0,
@@ -415,7 +418,7 @@ impl UdpSocket {
     pub async fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
         let data = match self.read_timeout_value() {
             Some(timeout) => {
-                crate::sys::linux::net::recv_timeout(
+                crate::sys::current::net::recv_timeout(
                     self.raw_fd(),
                     buf.len(),
                     libc::MSG_PEEK,
@@ -424,7 +427,7 @@ impl UdpSocket {
                 .await?
             }
             None => {
-                crate::sys::linux::net::recv(NetOp::Recv {
+                crate::sys::current::net::recv(NetOp::Recv {
                     fd: self.raw_fd(),
                     len: buf.len(),
                     flags: libc::MSG_PEEK,
@@ -442,13 +445,13 @@ impl UdpSocket {
     where
         A: ToSocketAddrs + Send + 'static,
     {
-        let addrs = crate::sys::linux::net::resolve_addrs(addr).await?;
+        let addrs = crate::sys::current::net::resolve_addrs(addr).await?;
         let mut last_error = None;
         let timeout = self.write_timeout_value();
         for addr in addrs {
             let result = match timeout {
                 Some(timeout) => {
-                    crate::sys::linux::net::send_to_timeout(
+                    crate::sys::current::net::send_to_timeout(
                         self.raw_fd(),
                         buf.to_vec(),
                         addr,
@@ -458,7 +461,7 @@ impl UdpSocket {
                     .await
                 }
                 None => {
-                    crate::sys::linux::net::send_to(NetOp::SendTo {
+                    crate::sys::current::net::send_to(NetOp::SendTo {
                         fd: self.raw_fd(),
                         target: addr,
                         data: buf.to_vec(),
@@ -485,11 +488,11 @@ impl UdpSocket {
     pub async fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
         let datagram = match self.read_timeout_value() {
             Some(timeout) => {
-                crate::sys::linux::net::recv_from_timeout(self.raw_fd(), buf.len(), 0, timeout)
+                crate::sys::current::net::recv_from_timeout(self.raw_fd(), buf.len(), 0, timeout)
                     .await?
             }
             None => {
-                crate::sys::linux::net::recv_from(NetOp::RecvFrom {
+                crate::sys::current::net::recv_from(NetOp::RecvFrom {
                     fd: self.raw_fd(),
                     len: buf.len(),
                     flags: 0,
@@ -506,7 +509,7 @@ impl UdpSocket {
     pub async fn peek_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
         let datagram = match self.read_timeout_value() {
             Some(timeout) => {
-                crate::sys::linux::net::recv_from_timeout(
+                crate::sys::current::net::recv_from_timeout(
                     self.raw_fd(),
                     buf.len(),
                     libc::MSG_PEEK,
@@ -515,7 +518,7 @@ impl UdpSocket {
                 .await?
             }
             None => {
-                crate::sys::linux::net::recv_from(NetOp::RecvFrom {
+                crate::sys::current::net::recv_from(NetOp::RecvFrom {
                     fd: self.raw_fd(),
                     len: buf.len(),
                     flags: libc::MSG_PEEK,
@@ -530,39 +533,39 @@ impl UdpSocket {
 
     /// Duplicates the underlying UDP socket.
     pub async fn try_clone(&self) -> io::Result<Self> {
-        crate::sys::linux::net::duplicate(self.raw_fd())
+        crate::sys::current::net::duplicate(self.raw_fd())
             .await
             .map(Self::from_owned_fd)
     }
 
     /// Returns the local socket address of this socket.
     pub fn local_addr(&self) -> io::Result<SocketAddr> {
-        crate::sys::linux::net::local_addr(self.raw_fd())
+        crate::sys::current::net::local_addr(self.raw_fd())
     }
 
     /// Returns the connected peer address, if the socket has been connected.
     pub fn peer_addr(&self) -> io::Result<SocketAddr> {
-        crate::sys::linux::net::peer_addr(self.raw_fd())
+        crate::sys::current::net::peer_addr(self.raw_fd())
     }
 
     /// Reads the `SO_BROADCAST` setting.
     pub fn broadcast(&self) -> io::Result<bool> {
-        crate::sys::linux::net::broadcast(self.raw_fd())
+        crate::sys::current::net::broadcast(self.raw_fd())
     }
 
     /// Enables or disables `SO_BROADCAST`.
     pub fn set_broadcast(&self, enabled: bool) -> io::Result<()> {
-        crate::sys::linux::net::set_broadcast(self.raw_fd(), enabled)
+        crate::sys::current::net::set_broadcast(self.raw_fd(), enabled)
     }
 
     /// Reads the socket's IP time-to-live value.
     pub fn ttl(&self) -> io::Result<u32> {
-        crate::sys::linux::net::ttl(self.raw_fd())
+        crate::sys::current::net::ttl(self.raw_fd())
     }
 
     /// Sets the socket's IP time-to-live value.
     pub fn set_ttl(&self, ttl: u32) -> io::Result<()> {
-        crate::sys::linux::net::set_ttl(self.raw_fd(), ttl)
+        crate::sys::current::net::set_ttl(self.raw_fd(), ttl)
     }
 
     /// Returns the read timeout used by async receive operations on this handle.
@@ -628,13 +631,13 @@ impl HyperRead for TcpStream {
 
         if this.pending_read.is_none() {
             this.pending_read = Some(match this.read_timeout_value() {
-                Some(timeout) => Box::pin(crate::sys::linux::net::recv_timeout(
+                Some(timeout) => Box::pin(crate::sys::current::net::recv_timeout(
                     this.raw_fd(),
                     buf.remaining(),
                     0,
                     timeout,
                 )),
-                None => crate::sys::linux::net::recv_future(this.raw_fd(), buf.remaining()),
+                None => crate::sys::current::net::recv_future(this.raw_fd(), buf.remaining()),
             });
         }
 
@@ -672,13 +675,13 @@ impl HyperWrite for TcpStream {
 
         if this.pending_write.is_none() {
             this.pending_write = Some(match this.write_timeout_value() {
-                Some(timeout) => Box::pin(crate::sys::linux::net::send_timeout(
+                Some(timeout) => Box::pin(crate::sys::current::net::send_timeout(
                     this.raw_fd(),
                     buf.to_vec(),
                     0,
                     timeout,
                 )),
-                None => crate::sys::linux::net::send_future(this.raw_fd(), buf.to_vec()),
+                None => crate::sys::current::net::send_future(this.raw_fd(), buf.to_vec()),
             });
         }
 
@@ -708,7 +711,7 @@ impl HyperWrite for TcpStream {
     fn poll_shutdown(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), io::Error>> {
         let this = self.get_mut();
         if this.pending_shutdown.is_none() {
-            this.pending_shutdown = Some(crate::sys::linux::net::shutdown_future(
+            this.pending_shutdown = Some(crate::sys::current::net::shutdown_future(
                 this.raw_fd(),
                 Shutdown::Write,
             ));

lib/runtime/src/op/completion.rs

@@ -6,7 +6,7 @@ use std::sync::atomic::{AtomicBool, Ordering};
 use std::sync::{Arc, Mutex};
 use std::task::{Context, Poll, Waker};
 
-use crate::platform::linux_x86_64::runtime::{ThreadHandle, current_thread_handle};
+use crate::platform::current::runtime::{ThreadHandle, current_thread_handle};
 
 type CancelCallback = Box<dyn FnOnce() + Send + 'static>;
 

lib/runtime/src/platform/linux_x86_64/runtime.rs

@@ -13,16 +13,12 @@ use std::task::{Context, Poll, RawWaker, RawWakerVTable, Waker};
 use std::time::Duration;
 
 use super::driver::{Driver, ThreadNotifier, create_driver, monotonic_now};
+use crate::platform::runtime_shared::{
+    IntervalCallback, LocalBoxFuture, LocalTask, LocalTaskQueue, MICROTASK_STARVATION_THRESHOLD,
+    MacroTaskQueue, SendTask,
+};
 use crate::trace_targets;
 
-type LocalTask = Box<dyn FnOnce() + 'static>;
-type SendTask = Box<dyn FnOnce() + Send + 'static>;
-type LocalBoxFuture = Pin<Box<dyn Future<Output = ()> + 'static>>;
-
-/// If the microtask queue runs more than this many tasks in a single turn
-/// without yielding to the macrotask queue, a warning is emitted.
-const MICROTASK_STARVATION_THRESHOLD: u64 = 1000;
-
 struct MacroTask {
     task: LocalTask,
     /// Wall time at which this task entered the local queue. Populated only
@@ -493,6 +489,99 @@ pub fn run() {
     }
 }
 
+/// Drains ready work on the current runtime thread without blocking for future work.
+///
+/// Unlike [`run`], this returns as soon as there are no immediately runnable
+/// microtasks or macrotasks left. It is intended for host integrations that
+/// need to re-enter the scheduler while an outer platform loop remains active.
+pub fn run_until_stalled() {
+    let _ = current_thread();
+
+    loop {
+        drain_all();
+
+        let mut microtasks_run: u64 = 0;
+        while let Some(task) = pop_microtask() {
+            task();
+            microtasks_run += 1;
+            drain_all();
+        }
+        if microtasks_run >= MICROTASK_STARVATION_THRESHOLD {
+            tracing::warn!(
+                target: trace_targets::SCHEDULER,
+                event = "microtask_starvation",
+                count = microtasks_run,
+                "microtask queue ran {microtasks_run} tasks in a single turn; macrotask handlers may be starved",
+            );
+        }
+
+        if let Some(task) = pop_macrotask() {
+            task();
+            continue;
+        }
+
+        drain_all();
+
+        if has_ready_work() {
+            continue;
+        }
+
+        current_thread()
+            .shared
+            .closing
+            .store(false, Ordering::Release);
+        return;
+    }
+}
+
+/// Drains already-queued work on the current runtime thread without polling the
+/// driver for timers or I/O readiness.
+///
+/// This is intended for host integrations that need to flush application work
+/// from inside a host callback without re-entering timer callbacks.
+pub fn run_ready_tasks() {
+    let _ = current_thread();
+
+    loop {
+        drain_remote_tasks();
+        drain_completed_workers();
+
+        let mut microtasks_run: u64 = 0;
+        while let Some(task) = pop_microtask() {
+            task();
+            microtasks_run += 1;
+            drain_remote_tasks();
+            drain_completed_workers();
+        }
+        if microtasks_run >= MICROTASK_STARVATION_THRESHOLD {
+            tracing::warn!(
+                target: trace_targets::SCHEDULER,
+                event = "microtask_starvation",
+                count = microtasks_run,
+                "microtask queue ran {microtasks_run} tasks in a single turn; macrotask handlers may be starved",
+            );
+        }
+
+        if let Some(task) = pop_macrotask() {
+            task();
+            continue;
+        }
+
+        drain_remote_tasks();
+        drain_completed_workers();
+
+        if has_ready_work() {
+            continue;
+        }
+
+        current_thread()
+            .shared
+            .closing
+            .store(false, Ordering::Release);
+        return;
+    }
+}
+
 fn drain_all() {
     drain_driver_events();
     drain_remote_tasks();
@@ -592,8 +681,8 @@ struct ThreadState {
     driver: Driver,
     shared: Arc<ThreadShared>,
     worker_completion: Option<Arc<WorkerCompletion>>,
-    local_microtasks: RefCell<VecDeque<LocalTask>>,
+    local_microtasks: RefCell<LocalTaskQueue>,
-    local_macrotasks: RefCell<VecDeque<MacroTask>>,
+    local_macrotasks: RefCell<MacroTaskQueue<MacroTask>>,
     timers: RefCell<TimerHeap>,
     /// Zero-delay intervals bypasses the timer heap entirely. Each entry
     /// re-enqueues itself as a macrotask on every turn.

lib/runtime/src/platform/macos_aarch64/driver.rs

@@ -0,0 +1,504 @@
+//! Public runtime driver primitives for macOS.
+
+use std::cell::{Cell, RefCell};
+use std::collections::HashMap;
+use std::io;
+use std::os::fd::RawFd;
+use std::sync::Arc;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::time::Duration;
+
+use crate::op::completion::CompletionHandle;
+
+type FdCompletion = CompletionHandle<io::Result<()>>;
+
+#[derive(Debug, Clone, Copy, Eq, PartialEq, Hash)]
+pub(crate) struct FdReadinessToken(u64);
+
+#[derive(Debug, Clone, Copy, Eq, PartialEq, Hash)]
+pub(crate) enum FdInterest {
+    Readable,
+    Writable,
+}
+
+#[derive(Debug, Clone, Copy, Eq, PartialEq, Hash)]
+struct FdKey {
+    fd: RawFd,
+    interest: FdInterest,
+}
+
+struct FdWaiter {
+    token: FdReadinessToken,
+    completion: FdCompletion,
+}
+
+#[derive(Clone)]
+struct NotifierInner {
+    write_fd: RawFd,
+    closed: Arc<AtomicBool>,
+}
+
+impl NotifierInner {
+    fn notify(&self) -> io::Result<()> {
+        if self.closed.load(Ordering::Acquire) {
+            return Err(io::Error::new(
+                io::ErrorKind::BrokenPipe,
+                "target runtime driver is closed",
+            ));
+        }
+
+        let byte = 1u8;
+        let written = unsafe {
+            libc::write(
+                self.write_fd,
+                &byte as *const u8 as *const libc::c_void,
+                std::mem::size_of::<u8>(),
+            )
+        };
+        if written < 0 {
+            let error = io::Error::last_os_error();
+            if error.kind() == io::ErrorKind::WouldBlock {
+                return Ok(());
+            }
+            return Err(error);
+        }
+
+        Ok(())
+    }
+}
+
+#[derive(Clone)]
+/// Cross-thread notifier for a runtime thread's driver.
+pub struct ThreadNotifier {
+    inner: NotifierInner,
+}
+
+impl ThreadNotifier {
+    /// Sends a wake notification to the target runtime thread.
+    pub fn notify(&self) -> io::Result<()> {
+        self.inner.notify()
+    }
+}
+
+#[derive(Debug, Default, Clone, Copy, Eq, PartialEq)]
+/// Readiness information returned by [`Driver::poll`].
+pub struct ReadyEvents {
+    /// One or more timer expirations are pending.
+    pub timer: bool,
+    /// One or more cross-thread wake notifications are pending.
+    pub wake: bool,
+}
+
+/// Low-level macOS runtime driver backed by `kqueue` and a wake pipe.
+pub struct Driver {
+    kqueue_fd: RawFd,
+    wake_read_fd: RawFd,
+    wake_write_fd: RawFd,
+    closed: Arc<AtomicBool>,
+    timer_deadline: Cell<Option<Duration>>,
+    pending_wakes: Cell<u64>,
+    pending_timers: Cell<u64>,
+    next_fd_token: Cell<u64>,
+    fd_waiters: RefCell<HashMap<FdKey, FdWaiter>>,
+}
+
+/// Creates a new driver and its paired [`ThreadNotifier`].
+pub fn create() -> io::Result<(Driver, ThreadNotifier)> {
+    create_driver()
+}
+
+/// Creates a new driver and its paired [`ThreadNotifier`].
+pub fn create_driver() -> io::Result<(Driver, ThreadNotifier)> {
+    let kqueue_fd = cvt(unsafe { libc::kqueue() })?;
+
+    let mut pipe_fds = [0; 2];
+    cvt(unsafe { libc::pipe(pipe_fds.as_mut_ptr()) })?;
+    let wake_read_fd = pipe_fds[0];
+    let wake_write_fd = pipe_fds[1];
+
+    set_nonblocking(wake_read_fd)?;
+    set_nonblocking(wake_write_fd)?;
+
+    let event = libc::kevent {
+        ident: wake_read_fd as usize,
+        filter: libc::EVFILT_READ,
+        flags: libc::EV_ADD | libc::EV_ENABLE,
+        fflags: 0,
+        data: 0,
+        udata: std::ptr::null_mut(),
+    };
+
+    let submitted = unsafe {
+        libc::kevent(
+            kqueue_fd,
+            &event,
+            1,
+            std::ptr::null_mut(),
+            0,
+            std::ptr::null(),
+        )
+    };
+    if submitted < 0 {
+        let error = io::Error::last_os_error();
+        unsafe {
+            libc::close(wake_read_fd);
+            libc::close(wake_write_fd);
+            libc::close(kqueue_fd);
+        }
+        return Err(error);
+    }
+
+    let closed = Arc::new(AtomicBool::new(false));
+    let driver = Driver {
+        kqueue_fd,
+        wake_read_fd,
+        wake_write_fd,
+        closed: Arc::clone(&closed),
+        timer_deadline: Cell::new(None),
+        pending_wakes: Cell::new(0),
+        pending_timers: Cell::new(0),
+        next_fd_token: Cell::new(1),
+        fd_waiters: RefCell::new(HashMap::new()),
+    };
+
+    let notifier = ThreadNotifier {
+        inner: NotifierInner {
+            write_fd: wake_write_fd,
+            closed,
+        },
+    };
+
+    Ok((driver, notifier))
+}
+
+impl Driver {
+    pub(crate) fn bind_current_thread(&self) {}
+
+    pub(crate) fn unbind_current_thread(&self) {}
+
+    /// Polls the driver without blocking.
+    pub fn poll(&self) -> io::Result<Option<ReadyEvents>> {
+        let mut pending = ReadyEvents::default();
+        if self.pending_wakes.get() > 0 {
+            pending.wake = true;
+        }
+        if self.pending_timers.get() > 0 {
+            pending.timer = true;
+        }
+        if pending.wake || pending.timer {
+            return Ok(Some(pending));
+        }
+        self.process(Some(Duration::ZERO))
+    }
+
+    /// Blocks until at least one event is available.
+    pub fn wait(&self) -> io::Result<()> {
+        let now = monotonic_now()?;
+        let timeout = self
+            .timer_deadline
+            .get()
+            .map(|deadline| deadline.saturating_sub(now));
+        let _ = self.process(timeout)?;
+        Ok(())
+    }
+
+    /// Updates the currently armed timer deadline.
+    pub fn rearm_timer(&self, deadline: Option<Duration>) -> io::Result<()> {
+        self.timer_deadline.set(deadline);
+        Ok(())
+    }
+
+    /// Drains the accumulated wake notification count.
+    pub fn drain_wake(&self) -> io::Result<u64> {
+        let wakes = self.pending_wakes.replace(0);
+        if wakes == 0 {
+            Err(io::Error::new(
+                io::ErrorKind::WouldBlock,
+                "no wake events are pending",
+            ))
+        } else {
+            Ok(wakes)
+        }
+    }
+
+    /// Drains the accumulated timer-expiration count.
+    pub fn drain_timer(&self) -> io::Result<u64> {
+        let timers = self.pending_timers.replace(0);
+        if timers == 0 {
+            Err(io::Error::new(
+                io::ErrorKind::WouldBlock,
+                "no timer events are pending",
+            ))
+        } else {
+            Ok(timers)
+        }
+    }
+
+    pub(crate) fn register_fd_readiness(
+        &self,
+        fd: RawFd,
+        interest: FdInterest,
+        completion: FdCompletion,
+    ) -> io::Result<FdReadinessToken> {
+        let key = FdKey { fd, interest };
+        let removed_stale_waiter = {
+            let mut waiters = self.fd_waiters.borrow_mut();
+            match waiters.get(&key) {
+                Some(waiter) if !waiter.completion.is_interested() => {
+                    waiters.remove(&key);
+                    true
+                }
+                Some(_) => {
+                    return Err(io::Error::new(
+                        io::ErrorKind::AlreadyExists,
+                        "fd readiness already has a waiter for this interest",
+                    ));
+                }
+                None => false,
+            }
+        };
+        if removed_stale_waiter {
+            let _ = self.update_fd_interest(key, libc::EV_DELETE);
+        }
+
+        let token = self.allocate_fd_token();
+        self.update_fd_interest(key, libc::EV_ADD | libc::EV_ENABLE | libc::EV_ONESHOT)?;
+        self.fd_waiters
+            .borrow_mut()
+            .insert(key, FdWaiter { token, completion });
+        Ok(token)
+    }
+
+    pub(crate) fn cancel_fd_readiness(&self, token: FdReadinessToken) {
+        let mut empty_key = None;
+        {
+            let mut waiters = self.fd_waiters.borrow_mut();
+            for (key, entry) in waiters.iter() {
+                if entry.token == token {
+                    empty_key = Some(*key);
+                    break;
+                }
+            }
+
+            if let Some(key) = empty_key {
+                waiters.remove(&key);
+            }
+        }
+
+        if let Some(key) = empty_key {
+            let _ = self.update_fd_interest(key, libc::EV_DELETE);
+        }
+    }
+
+    fn process(&self, timeout: Option<Duration>) -> io::Result<Option<ReadyEvents>> {
+        let mut ready = ReadyEvents::default();
+
+        let mut events = [unsafe { std::mem::zeroed::<libc::kevent>() }; 16];
+        let timeout_spec = timeout_to_timespec(timeout);
+        let timeout_ptr = timeout_spec
+            .as_ref()
+            .map_or(std::ptr::null(), |value| value as *const libc::timespec);
+
+        let result = unsafe {
+            libc::kevent(
+                self.kqueue_fd,
+                std::ptr::null(),
+                0,
+                events.as_mut_ptr(),
+                events.len() as i32,
+                timeout_ptr,
+            )
+        };
+        if result < 0 {
+            let error = io::Error::last_os_error();
+            if error.kind() != io::ErrorKind::Interrupted {
+                return Err(error);
+            }
+        }
+
+        let mut saw_any = false;
+        let count = result.max(0) as usize;
+        if count > 0 {
+            saw_any = true;
+            for event in events.iter().take(count) {
+                if event.ident as RawFd == self.wake_read_fd {
+                    ready.wake = true;
+                    let wakes = drain_wake_pipe(self.wake_read_fd)?;
+                    self.pending_wakes
+                        .set(self.pending_wakes.get().saturating_add(wakes));
+                } else if let Some(interest) = interest_from_filter(event.filter) {
+                    self.complete_fd_waiters(event.ident as RawFd, interest, event);
+                }
+            }
+        }
+
+        if let Some(deadline) = self.timer_deadline.get()
+            && monotonic_now()? >= deadline
+        {
+            ready.timer = true;
+            saw_any = true;
+            self.timer_deadline.set(None);
+            self.pending_timers
+                .set(self.pending_timers.get().saturating_add(1));
+        }
+
+        if saw_any { Ok(Some(ready)) } else { Ok(None) }
+    }
+
+    fn allocate_fd_token(&self) -> FdReadinessToken {
+        let token = self.next_fd_token.get();
+        self.next_fd_token.set(
+            token
+                .checked_add(1)
+                .expect("fd readiness token space exhausted"),
+        );
+        FdReadinessToken(token)
+    }
+
+    fn update_fd_interest(&self, key: FdKey, flags: u16) -> io::Result<()> {
+        let event = libc::kevent {
+            ident: key.fd as usize,
+            filter: filter_for_interest(key.interest),
+            flags,
+            fflags: 0,
+            data: 0,
+            udata: std::ptr::null_mut(),
+        };
+        let submitted = unsafe {
+            libc::kevent(
+                self.kqueue_fd,
+                &event,
+                1,
+                std::ptr::null_mut(),
+                0,
+                std::ptr::null(),
+            )
+        };
+        if submitted < 0 {
+            Err(io::Error::last_os_error())
+        } else {
+            Ok(())
+        }
+    }
+
+    fn complete_fd_waiters(&self, fd: RawFd, interest: FdInterest, event: &libc::kevent) {
+        let key = FdKey { fd, interest };
+        let waiter = self.fd_waiters.borrow_mut().remove(&key);
+        let Some(waiter) = waiter else {
+            return;
+        };
+
+        let result = fd_event_result(event, interest);
+        waiter.completion.complete(result);
+    }
+}
+
+impl Drop for Driver {
+    fn drop(&mut self) {
+        self.closed.store(true, Ordering::Release);
+        unsafe {
+            libc::close(self.wake_read_fd);
+            libc::close(self.wake_write_fd);
+            libc::close(self.kqueue_fd);
+        }
+    }
+}
+
+/// Returns the current monotonic clock reading.
+pub fn monotonic_now() -> io::Result<Duration> {
+    let mut now = std::mem::MaybeUninit::<libc::timespec>::uninit();
+    let result = unsafe { libc::clock_gettime(libc::CLOCK_MONOTONIC, now.as_mut_ptr()) };
+    if result < 0 {
+        return Err(io::Error::last_os_error());
+    }
+
+    let now = unsafe { now.assume_init() };
+    Ok(Duration::new(now.tv_sec as u64, now.tv_nsec as u32))
+}
+
+fn cvt(value: libc::c_int) -> io::Result<libc::c_int> {
+    if value < 0 {
+        Err(io::Error::last_os_error())
+    } else {
+        Ok(value)
+    }
+}
+
+fn filter_for_interest(interest: FdInterest) -> i16 {
+    match interest {
+        FdInterest::Readable => libc::EVFILT_READ,
+        FdInterest::Writable => libc::EVFILT_WRITE,
+    }
+}
+
+fn interest_from_filter(filter: i16) -> Option<FdInterest> {
+    if filter == libc::EVFILT_READ {
+        Some(FdInterest::Readable)
+    } else if filter == libc::EVFILT_WRITE {
+        Some(FdInterest::Writable)
+    } else {
+        None
+    }
+}
+
+fn fd_event_result(event: &libc::kevent, interest: FdInterest) -> io::Result<()> {
+    if event.flags & libc::EV_ERROR != 0 && event.data != 0 {
+        Err(io::Error::from_raw_os_error(event.data as i32))
+    } else if event.flags & libc::EV_EOF != 0 && interest == FdInterest::Writable {
+        Err(io::Error::new(
+            io::ErrorKind::BrokenPipe,
+            "fd write side reached EOF",
+        ))
+    } else {
+        Ok(())
+    }
+}
+
+fn set_nonblocking(fd: RawFd) -> io::Result<()> {
+    let flags = cvt(unsafe { libc::fcntl(fd, libc::F_GETFL) })?;
+    cvt(unsafe { libc::fcntl(fd, libc::F_SETFL, flags | libc::O_NONBLOCK) })?;
+    Ok(())
+}
+
+fn timeout_to_timespec(timeout: Option<Duration>) -> Option<libc::timespec> {
+    timeout.map(|value| libc::timespec {
+        tv_sec: value.as_secs() as libc::time_t,
+        tv_nsec: value.subsec_nanos() as libc::c_long,
+    })
+}
+
+fn drain_wake_pipe(fd: RawFd) -> io::Result<u64> {
+    let mut wakes = 0u64;
+    let mut buf = [0u8; 256];
+
+    loop {
+        let read = unsafe {
+            libc::read(
+                fd,
+                buf.as_mut_ptr() as *mut libc::c_void,
+                buf.len() as libc::size_t,
+            )
+        };
+
+        if read > 0 {
+            wakes = wakes.saturating_add(read as u64);
+            continue;
+        }
+
+        if read == 0 {
+            break;
+        }
+
+        let error = io::Error::last_os_error();
+        if error.kind() == io::ErrorKind::WouldBlock {
+            break;
+        }
+        if error.kind() == io::ErrorKind::Interrupted {
+            continue;
+        }
+
+        return Err(error);
+    }
+
+    Ok(wakes.max(1))
+}

lib/runtime/src/platform/macos_aarch64/mod.rs

@@ -0,0 +1,2 @@
+pub mod driver;
+pub mod runtime;

lib/runtime/src/platform/mod.rs

@@ -1,2 +1,11 @@
+pub(crate) mod runtime_shared;
+
 #[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 pub mod linux_x86_64;
+#[cfg(all(target_os = "macos", target_arch = "aarch64"))]
+pub mod macos_aarch64;
+
+#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
+pub use linux_x86_64 as current;
+#[cfg(all(target_os = "macos", target_arch = "aarch64"))]
+pub use macos_aarch64 as current;

lib/runtime/src/platform/runtime_shared.rs

@@ -0,0 +1,17 @@
+use std::cell::RefCell;
+use std::collections::VecDeque;
+use std::future::Future;
+use std::pin::Pin;
+use std::rc::Rc;
+
+pub(crate) type LocalTask = Box<dyn FnOnce() + 'static>;
+pub(crate) type SendTask = Box<dyn FnOnce() + Send + 'static>;
+pub(crate) type LocalBoxFuture = Pin<Box<dyn Future<Output = ()> + 'static>>;
+pub(crate) type IntervalCallback = Rc<RefCell<Box<dyn FnMut()>>>;
+
+/// If the microtask queue runs more than this many tasks in a single turn
+/// without yielding to the macrotask queue, a warning is emitted.
+pub(crate) const MICROTASK_STARVATION_THRESHOLD: u64 = 1000;
+
+pub(crate) type LocalTaskQueue = VecDeque<LocalTask>;
+pub(crate) type MacroTaskQueue<T> = VecDeque<T>;

lib/runtime/src/stdio.rs

@@ -1,18 +1,23 @@
 //! Async standard-input helpers.
 
-use std::cell::Cell;
 use std::io;
 use std::os::fd::{AsRawFd, FromRawFd, OwnedFd, RawFd};
 use std::thread;
 
 use crate::op::completion::completion_for_current_thread;
+#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 use crate::platform::linux_x86_64::runtime::with_current_driver;
+#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 use crate::platform::linux_x86_64::uring::{IORING_OP_READ, IoUringCqe, IoUringSqe};
+#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
+use std::cell::Cell;
 
+#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 thread_local! {
     static STDIN_URING_SUPPORTED: Cell<Option<bool>> = const { Cell::new(None) };
 }
 
+#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 const FILE_CURSOR: u64 = u64::MAX;
 const READ_CHUNK_BYTES: usize = 1024;
 
@@ -60,17 +65,20 @@ impl Stdin {
 
     async fn read_chunk(&self) -> io::Result<Vec<u8>> {
         let fd = self.fd.as_raw_fd();
-        let support = STDIN_URING_SUPPORTED.with(Cell::get);
+        #[cfg(all(target_os = "linux", target_arch = "x86_64"))]
-        if support != Some(false) {
+        {
-            match submit_uring_read(fd, READ_CHUNK_BYTES).await {
+            let support = STDIN_URING_SUPPORTED.with(Cell::get);
-                Ok(bytes) => {
+            if support != Some(false) {
-                    STDIN_URING_SUPPORTED.with(|state| state.set(Some(true)));
+                match submit_uring_read(fd, READ_CHUNK_BYTES).await {
-                    return Ok(bytes);
+                    Ok(bytes) => {
+                        STDIN_URING_SUPPORTED.with(|state| state.set(Some(true)));
+                        return Ok(bytes);
+                    }
+                    Err(error) if should_fallback_to_offload(&error) => {
+                        STDIN_URING_SUPPORTED.with(|state| state.set(Some(false)));
+                    }
+                    Err(error) => return Err(error),
                 }
-                Err(error) if should_fallback_to_offload(&error) => {
-                    STDIN_URING_SUPPORTED.with(|state| state.set(Some(false)));
-                }
-                Err(error) => return Err(error),
             }
         }
 
@@ -99,6 +107,7 @@ async fn offload<T: Send + 'static>(
     future.await
 }
 
+#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 async fn submit_uring_read(fd: RawFd, len: usize) -> io::Result<Vec<u8>> {
     let mut buffer = vec![0; len];
     let ptr = buffer.as_mut_ptr();
@@ -120,6 +129,7 @@ async fn submit_uring_read(fd: RawFd, len: usize) -> io::Result<Vec<u8>> {
     .await
 }
 
+#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 async fn submit_uring<T: Send + 'static, M>(
     fill: impl FnOnce(&mut IoUringSqe),
     map: M,
@@ -144,13 +154,8 @@ where
 
 fn blocking_read(fd: RawFd, buffer: &mut [u8]) -> io::Result<usize> {
     loop {
-        let read = unsafe {
+        let read =
-            libc::read(
+            unsafe { libc::read(fd, buffer.as_mut_ptr().cast::<libc::c_void>(), buffer.len()) };
-                fd,
-                buffer.as_mut_ptr().cast::<libc::c_void>(),
-                buffer.len(),
-            )
-        };
         if read >= 0 {
             return Ok(read as usize);
         }
@@ -167,6 +172,7 @@ fn decode_line(bytes: Vec<u8>) -> io::Result<String> {
     String::from_utf8(bytes).map_err(|error| io::Error::new(io::ErrorKind::InvalidData, error))
 }
 
+#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 fn cqe_to_result(cqe: IoUringCqe) -> io::Result<i32> {
     if cqe.res < 0 {
         Err(io::Error::from_raw_os_error(-cqe.res))
@@ -175,6 +181,7 @@ fn cqe_to_result(cqe: IoUringCqe) -> io::Result<i32> {
     }
 }
 
+#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 fn should_fallback_to_offload(error: &io::Error) -> bool {
     matches!(
         error.raw_os_error(),

lib/runtime/src/sys/linux/channel.rs

@@ -1,7 +1,7 @@
 //! Linux channel wake helpers.
 
 use crate::op::completion::{CompletionFuture, CompletionHandle, completion};
-use crate::platform::linux_x86_64::runtime::try_current_thread_handle;
+use crate::platform::current::runtime::try_current_thread_handle;
 
 pub(crate) fn runtime_waiter<T: Send + 'static>() -> (CompletionFuture<T>, CompletionHandle<T>) {
     let owner = try_current_thread_handle()

lib/runtime/src/sys/linux/fd.rs

@@ -0,0 +1,44 @@
+//! Linux fd readiness backend.
+
+use std::io;
+use std::os::fd::RawFd;
+
+use crate::op::completion::completion_for_current_thread;
+use crate::platform::current::runtime::with_current_driver;
+use crate::platform::linux_x86_64::uring::{IORING_OP_POLL_ADD, IoUringCqe};
+
+/// Waits until `fd` becomes readable or reports an error/hangup condition.
+pub async fn wait_readable(fd: RawFd) -> io::Result<()> {
+    submit_poll(fd, libc::POLLIN | libc::POLLERR | libc::POLLHUP).await
+}
+
+async fn submit_poll(fd: RawFd, mask: i16) -> io::Result<()> {
+    let (future, handle) = completion_for_current_thread::<io::Result<()>>();
+    let callback_handle = handle.clone();
+    let token = with_current_driver(|driver| {
+        driver.submit_operation(
+            move |sqe| {
+                sqe.opcode = IORING_OP_POLL_ADD;
+                sqe.fd = fd;
+                sqe.len = 0;
+                sqe.op_flags = mask as u32;
+            },
+            move |cqe| {
+                callback_handle.complete(cqe_to_result(cqe));
+            },
+        )
+    })?;
+
+    handle.set_cancel(move || {
+        let _ = with_current_driver(|driver| driver.cancel_operation(token));
+    });
+
+    future.await
+}
+
+fn cqe_to_result(cqe: IoUringCqe) -> io::Result<()> {
+    if cqe.res < 0 {
+        return Err(io::Error::from_raw_os_error(-cqe.res));
+    }
+    Ok(())
+}

lib/runtime/src/sys/linux/mod.rs

@@ -1,5 +1,6 @@
 //! Linux backend modules.
 
 pub mod channel;
+pub mod fd;
 pub mod fs;
 pub mod net;

lib/runtime/src/sys/linux/net.rs

@@ -803,13 +803,9 @@ where
     let (future, handle) = completion_for_current_thread::<io::Result<T>>();
     let callback_handle = handle.clone();
     let token = with_current_driver(|driver| {
-        driver.submit_operation_with_linked_timeout(
+        driver.submit_operation_with_linked_timeout(fill, timeout, move |cqe| {
-            fill,
+            callback_handle.complete(map(cqe));
-            timeout,
+        })
-            move |cqe| {
-                callback_handle.complete(map(cqe));
-            },
-        )
     })?;
 
     handle.set_cancel(move || {
@@ -1079,7 +1075,6 @@ fn send_sync(fd: RawFd, data: Vec<u8>, flags: i32) -> io::Result<usize> {
     cvt_long(written).map(|written| written as usize)
 }
 
-
 fn recv_sync(fd: RawFd, len: usize, flags: i32) -> io::Result<Vec<u8>> {
     let mut buffer = vec![0; len];
     let read = unsafe {
@@ -1127,7 +1122,6 @@ fn close_sync(fd: RawFd) -> io::Result<()> {
     cvt(unsafe { libc::close(fd) }).map(|_| ())
 }
 
-
 /// Wrapper making `Box<libc::iovec>` sendable across the async CQE boundary.
 ///
 /// Safety: `iov_base` points into a `Vec<u8>` that is owned by the same

lib/runtime/src/sys/macos/channel.rs

@@ -0,0 +1,10 @@
+//! macOS channel wake helpers.
+
+use crate::op::completion::{CompletionFuture, CompletionHandle, completion};
+use crate::platform::current::runtime::try_current_thread_handle;
+
+pub(crate) fn runtime_waiter<T: Send + 'static>() -> (CompletionFuture<T>, CompletionHandle<T>) {
+    let owner = try_current_thread_handle()
+        .expect("async channel operations must be polled on a runtime thread");
+    completion(owner)
+}

lib/runtime/src/sys/macos/fd.rs

@@ -0,0 +1,49 @@
+//! macOS fd readiness backend.
+
+use std::io;
+use std::os::fd::RawFd;
+
+use crate::op::completion::completion_for_current_thread;
+use crate::platform::current::driver::FdInterest;
+use crate::platform::current::runtime::{
+    cancel_fd_readiness, current_thread_handle, with_current_driver,
+};
+
+/// Waits until `fd` becomes readable or reports an error/hangup condition.
+pub async fn wait_readable(fd: RawFd) -> io::Result<()> {
+    wait_fd_readiness(fd, FdInterest::Readable).await
+}
+
+/// Waits until `fd` becomes writable or reports an error/hangup condition.
+pub async fn wait_writable(fd: RawFd) -> io::Result<()> {
+    wait_fd_readiness(fd, FdInterest::Writable).await
+}
+
+async fn wait_fd_readiness(fd: RawFd, interest: FdInterest) -> io::Result<()> {
+    let (future, handle) = completion_for_current_thread::<io::Result<()>>();
+    let owner = current_thread_handle();
+    let token =
+        with_current_driver(|driver| driver.register_fd_readiness(fd, interest, handle.clone()));
+    match token {
+        Ok(token) => {
+            handle.set_cancel({
+                let handle = handle.clone();
+                move || {
+                    let queued_handle = handle.clone();
+                    let queued = owner.queue_task(move || {
+                        cancel_fd_readiness(token);
+                        queued_handle.finish(None);
+                    });
+                    if !queued {
+                        handle.finish(None);
+                    }
+                }
+            });
+        }
+        Err(error) => {
+            handle.complete(Err(error));
+        }
+    }
+
+    future.await
+}

lib/runtime/src/sys/macos/fs.rs

@@ -0,0 +1,498 @@
+//! macOS filesystem backend.
+
+use std::collections::VecDeque;
+use std::ffi::CString;
+use std::future::poll_fn;
+use std::io;
+use std::os::fd::{FromRawFd, OwnedFd};
+use std::os::unix::ffi::OsStrExt;
+use std::os::unix::fs::{FileTypeExt, MetadataExt, OpenOptionsExt};
+use std::path::PathBuf;
+use std::sync::OnceLock;
+use std::sync::atomic::{AtomicBool, Ordering};
+use std::sync::{Arc, Mutex, mpsc};
+use std::task::{Context, Poll, Waker};
+use std::thread;
+
+use crate::op::completion::completion_for_current_thread;
+use crate::op::fs::{FileType, FsOp, MetadataTarget, RawDirEntry, RawMetadata};
+use crate::platform::current::runtime::{ThreadHandle, current_thread_handle};
+
+type BlockingTask = Box<dyn FnOnce() + Send + 'static>;
+
+static BLOCKING_POOL: OnceLock<io::Result<BlockingPool>> = OnceLock::new();
+const BLOCKING_QUEUE_CAPACITY: usize = 1024;
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum ExecutionPath {
+    Offload,
+}
+
+pub fn execution_path(_op: &FsOp) -> ExecutionPath {
+    ExecutionPath::Offload
+}
+
+pub async fn open(op: FsOp) -> io::Result<OwnedFd> {
+    let FsOp::Open { path, options } = op else {
+        unreachable!("open backend called with non-open op");
+    };
+
+    offload(move || {
+        let mut open = std::fs::OpenOptions::new();
+        open.read(options.read)
+            .write(options.write)
+            .append(options.append)
+            .truncate(options.truncate)
+            .create(options.create)
+            .create_new(options.create_new)
+            .mode(0o666);
+        let file = open.open(path)?;
+        Ok(unsafe { OwnedFd::from_raw_fd(std::os::fd::IntoRawFd::into_raw_fd(file)) })
+    })
+    .await
+}
+
+pub async fn read(op: FsOp) -> io::Result<Vec<u8>> {
+    let FsOp::Read { fd, offset, len } = op else {
+        unreachable!("read backend called with non-read op");
+    };
+
+    offload(move || {
+        let mut buffer = vec![0; len];
+        let read = match offset {
+            Some(offset) => unsafe {
+                libc::pread(
+                    fd,
+                    buffer.as_mut_ptr().cast::<libc::c_void>(),
+                    len,
+                    offset as libc::off_t,
+                )
+            },
+            None => unsafe { libc::read(fd, buffer.as_mut_ptr().cast::<libc::c_void>(), len) },
+        };
+        if read < 0 {
+            return Err(io::Error::last_os_error());
+        }
+        buffer.truncate(read as usize);
+        Ok(buffer)
+    })
+    .await
+}
+
+pub async fn write(op: FsOp) -> io::Result<usize> {
+    let FsOp::Write { fd, offset, data } = op else {
+        unreachable!("write backend called with non-write op");
+    };
+
+    offload(move || {
+        let written = match offset {
+            Some(offset) => unsafe {
+                libc::pwrite(
+                    fd,
+                    data.as_ptr().cast::<libc::c_void>(),
+                    data.len(),
+                    offset as libc::off_t,
+                )
+            },
+            None => unsafe { libc::write(fd, data.as_ptr().cast::<libc::c_void>(), data.len()) },
+        };
+        if written < 0 {
+            return Err(io::Error::last_os_error());
+        }
+        Ok(written as usize)
+    })
+    .await
+}
+
+pub async fn metadata(op: FsOp) -> io::Result<RawMetadata> {
+    let FsOp::Metadata {
+        target,
+        follow_symlinks,
+    } = op
+    else {
+        unreachable!("metadata backend called with non-metadata op");
+    };
+
+    offload(move || {
+        let metadata = match target {
+            MetadataTarget::Path(path) => {
+                if follow_symlinks {
+                    std::fs::metadata(path)
+                } else {
+                    std::fs::symlink_metadata(path)
+                }
+            }
+            MetadataTarget::File(fd) => {
+                let mut stat = unsafe { std::mem::zeroed::<libc::stat>() };
+                let result = unsafe { libc::fstat(fd, &mut stat) };
+                if result < 0 {
+                    return Err(io::Error::last_os_error());
+                }
+                return Ok(raw_metadata_from_stat(&stat));
+            }
+        }?;
+        Ok(raw_metadata_from_std(&metadata))
+    })
+    .await
+}
+
+pub async fn sync_all(op: FsOp) -> io::Result<()> {
+    let FsOp::SyncAll { fd } = op else {
+        unreachable!("sync_all backend called with non-sync_all op");
+    };
+
+    offload(move || cvt(unsafe { libc::fsync(fd) }).map(|_| ())).await
+}
+
+pub async fn sync_data(op: FsOp) -> io::Result<()> {
+    let FsOp::SyncData { fd } = op else {
+        unreachable!("sync_data backend called with non-sync_data op");
+    };
+
+    offload(move || cvt(unsafe { libc::fcntl(fd, libc::F_FULLFSYNC) }).map(|_| ())).await
+}
+
+pub async fn set_len(op: FsOp) -> io::Result<()> {
+    let FsOp::SetLen { fd, len } = op else {
+        unreachable!("set_len backend called with non-set_len op");
+    };
+
+    offload(move || cvt(unsafe { libc::ftruncate(fd, len as libc::off_t) }).map(|_| ())).await
+}
+
+pub async fn try_clone(op: FsOp) -> io::Result<OwnedFd> {
+    let FsOp::Duplicate { fd } = op else {
+        unreachable!("try_clone backend called with non-duplicate op");
+    };
+
+    offload(move || {
+        let duplicated = cvt(unsafe { libc::fcntl(fd, libc::F_DUPFD_CLOEXEC, 0) })?;
+        Ok(unsafe { OwnedFd::from_raw_fd(duplicated) })
+    })
+    .await
+}
+
+pub async fn create_dir(op: FsOp) -> io::Result<()> {
+    let FsOp::CreateDir { path, mode } = op else {
+        unreachable!("create_dir backend called with non-create_dir op");
+    };
+
+    offload(move || {
+        let c_path = path_to_c_string(path)?;
+        cvt(unsafe { libc::mkdir(c_path.as_ptr(), mode as libc::mode_t) }).map(|_| ())
+    })
+    .await
+}
+
+pub async fn remove_file(op: FsOp) -> io::Result<()> {
+    let FsOp::RemoveFile { path } = op else {
+        unreachable!("remove_file backend called with non-remove_file op");
+    };
+
+    offload(move || std::fs::remove_file(path)).await
+}
+
+pub async fn remove_dir(op: FsOp) -> io::Result<()> {
+    let FsOp::RemoveDir { path } = op else {
+        unreachable!("remove_dir backend called with non-remove_dir op");
+    };
+
+    offload(move || std::fs::remove_dir(path)).await
+}
+
+pub async fn rename(op: FsOp) -> io::Result<()> {
+    let FsOp::Rename { from, to } = op else {
+        unreachable!("rename backend called with non-rename op");
+    };
+
+    offload(move || std::fs::rename(from, to)).await
+}
+
+pub async fn close(op: FsOp) -> io::Result<()> {
+    let FsOp::Close { fd } = op else {
+        unreachable!("close backend called with non-close op");
+    };
+
+    offload(move || cvt(unsafe { libc::close(fd) }).map(|_| ())).await
+}
+
+pub fn read_dir(op: FsOp) -> io::Result<ReadDirStream> {
+    let FsOp::ReadDir { path } = op else {
+        unreachable!("read_dir backend called with non-read_dir op");
+    };
+
+    ReadDirStream::new(path)
+}
+
+pub struct ReadDirStream {
+    state: Arc<ReadDirState>,
+}
+
+impl ReadDirStream {
+    fn new(path: PathBuf) -> io::Result<Self> {
+        let state = Arc::new(ReadDirState::new(current_thread_handle()));
+        let producer = Arc::clone(&state);
+
+        if let Err(error) = spawn_blocking(Box::new(move || produce_dir_entries(path, producer))) {
+            state.release_pending();
+            return Err(error);
+        }
+
+        Ok(Self { state })
+    }
+
+    pub async fn next_entry(&mut self) -> io::Result<Option<RawDirEntry>> {
+        poll_fn(|cx| self.state.poll_next(cx)).await
+    }
+}
+
+struct ReadDirState {
+    owner: ThreadHandle,
+    queue: Mutex<VecDeque<io::Result<RawDirEntry>>>,
+    done: AtomicBool,
+    pending: AtomicBool,
+    wake_queued: AtomicBool,
+    waker: Mutex<Option<Waker>>,
+}
+
+impl ReadDirState {
+    fn new(owner: ThreadHandle) -> Self {
+        owner.begin_async_operation();
+        Self {
+            owner,
+            queue: Mutex::new(VecDeque::new()),
+            done: AtomicBool::new(false),
+            pending: AtomicBool::new(true),
+            wake_queued: AtomicBool::new(false),
+            waker: Mutex::new(None),
+        }
+    }
+
+    fn push(self: &Arc<Self>, entry: io::Result<RawDirEntry>) {
+        self.queue.lock().unwrap().push_back(entry);
+        self.notify();
+    }
+
+    fn finish(self: &Arc<Self>) {
+        self.done.store(true, Ordering::Release);
+        self.release_pending();
+        self.notify();
+    }
+
+    fn release_pending(&self) {
+        if self.pending.swap(false, Ordering::AcqRel) {
+            self.owner.finish_async_operation();
+        }
+    }
+
+    fn notify(self: &Arc<Self>) {
+        if self.wake_queued.swap(true, Ordering::AcqRel) {
+            return;
+        }
+
+        let state = Arc::clone(self);
+        if !self.owner.queue_task(move || {
+            state.wake_queued.store(false, Ordering::Release);
+            if let Some(waker) = state.waker.lock().unwrap().take() {
+                waker.wake();
+            }
+        }) {
+            self.wake_queued.store(false, Ordering::Release);
+        }
+    }
+
+    fn poll_next(&self, cx: &mut Context<'_>) -> Poll<io::Result<Option<RawDirEntry>>> {
+        if let Some(entry) = self.queue.lock().unwrap().pop_front() {
+            return Poll::Ready(entry.map(Some));
+        }
+
+        if self.done.load(Ordering::Acquire) {
+            return Poll::Ready(Ok(None));
+        }
+
+        *self.waker.lock().unwrap() = Some(cx.waker().clone());
+
+        if let Some(entry) = self.queue.lock().unwrap().pop_front() {
+            let _ = self.waker.lock().unwrap().take();
+            return Poll::Ready(entry.map(Some));
+        }
+
+        if self.done.load(Ordering::Acquire) {
+            let _ = self.waker.lock().unwrap().take();
+            return Poll::Ready(Ok(None));
+        }
+
+        Poll::Pending
+    }
+}
+
+impl Drop for ReadDirStream {
+    fn drop(&mut self) {
+        self.state.release_pending();
+    }
+}
+
+fn produce_dir_entries(path: PathBuf, state: Arc<ReadDirState>) {
+    match std::fs::read_dir(path) {
+        Ok(entries) => {
+            for entry in entries {
+                match entry {
+                    Ok(entry) => {
+                        let file_name = entry.file_name();
+                        state.push(Ok(RawDirEntry {
+                            path: entry.path(),
+                            file_name,
+                        }));
+                    }
+                    Err(error) => state.push(Err(error)),
+                }
+            }
+            state.finish();
+        }
+        Err(error) => {
+            state.push(Err(error));
+            state.finish();
+        }
+    }
+}
+
+async fn offload<T: Send + 'static>(
+    work: impl FnOnce() -> io::Result<T> + Send + 'static,
+) -> io::Result<T> {
+    let (future, handle) = completion_for_current_thread::<io::Result<T>>();
+    let handle_for_task = handle.clone();
+    if let Err(error) = spawn_blocking(Box::new(move || handle_for_task.complete(work()))) {
+        handle.complete(Err(error));
+    }
+    future.await
+}
+
+struct BlockingPool {
+    sender: mpsc::SyncSender<BlockingTask>,
+}
+
+impl BlockingPool {
+    fn spawn(&self, task: BlockingTask) -> io::Result<()> {
+        self.sender.try_send(task).map_err(|error| match error {
+            mpsc::TrySendError::Full(_) => io::Error::new(
+                io::ErrorKind::WouldBlock,
+                "filesystem blocking worker queue is full",
+            ),
+            mpsc::TrySendError::Disconnected(_) => io::Error::new(
+                io::ErrorKind::BrokenPipe,
+                "filesystem blocking worker pool has stopped",
+            ),
+        })
+    }
+}
+
+fn spawn_blocking(task: BlockingTask) -> io::Result<()> {
+    blocking_pool()?.spawn(task)
+}
+
+fn blocking_pool() -> io::Result<&'static BlockingPool> {
+    match BLOCKING_POOL.get_or_init(create_blocking_pool) {
+        Ok(pool) => Ok(pool),
+        Err(error) => Err(io::Error::new(error.kind(), error.to_string())),
+    }
+}
+
+fn create_blocking_pool() -> io::Result<BlockingPool> {
+    let (sender, receiver) = mpsc::sync_channel::<BlockingTask>(BLOCKING_QUEUE_CAPACITY);
+    let receiver = Arc::new(Mutex::new(receiver));
+    let worker_count = std::thread::available_parallelism()
+        .map(usize::from)
+        .unwrap_or(2)
+        .clamp(2, 4);
+    let mut spawned = 0usize;
+    let mut last_error = None;
+
+    for index in 0..worker_count {
+        let receiver = Arc::clone(&receiver);
+        match thread::Builder::new()
+            .name(format!("ruin-runtime-fs-offload-{index}"))
+            .spawn(move || {
+                loop {
+                    let task = receiver.lock().unwrap().recv();
+                    match task {
+                        Ok(task) => task(),
+                        Err(_) => break,
+                    }
+                }
+            }) {
+            Ok(_) => spawned += 1,
+            Err(error) => last_error = Some(error),
+        }
+    }
+
+    if spawned == 0 {
+        return Err(io::Error::other(
+            last_error.expect("at least one worker spawn should have been attempted"),
+        ));
+    }
+
+    Ok(BlockingPool { sender })
+}
+
+fn path_to_c_string(path: PathBuf) -> io::Result<CString> {
+    CString::new(path.as_os_str().as_bytes()).map_err(|_| {
+        io::Error::new(
+            io::ErrorKind::InvalidInput,
+            "path contains interior NUL bytes",
+        )
+    })
+}
+
+fn raw_metadata_from_std(metadata: &std::fs::Metadata) -> RawMetadata {
+    let file_type = metadata.file_type();
+    let kind = if file_type.is_file() {
+        FileType::File
+    } else if file_type.is_dir() {
+        FileType::Directory
+    } else if file_type.is_symlink() {
+        FileType::Symlink
+    } else if file_type.is_block_device() {
+        FileType::BlockDevice
+    } else if file_type.is_char_device() {
+        FileType::CharacterDevice
+    } else if file_type.is_fifo() {
+        FileType::Fifo
+    } else if file_type.is_socket() {
+        FileType::Socket
+    } else {
+        FileType::Unknown
+    };
+
+    RawMetadata {
+        file_type: kind,
+        mode: (metadata.mode() & 0o7777) as u16,
+        len: metadata.len(),
+    }
+}
+
+fn raw_metadata_from_stat(stat: &libc::stat) -> RawMetadata {
+    let kind = match stat.st_mode & libc::S_IFMT {
+        libc::S_IFREG => FileType::File,
+        libc::S_IFDIR => FileType::Directory,
+        libc::S_IFLNK => FileType::Symlink,
+        libc::S_IFBLK => FileType::BlockDevice,
+        libc::S_IFCHR => FileType::CharacterDevice,
+        libc::S_IFIFO => FileType::Fifo,
+        libc::S_IFSOCK => FileType::Socket,
+        _ => FileType::Unknown,
+    };
+
+    RawMetadata {
+        file_type: kind,
+        mode: stat.st_mode & 0o7777,
+        len: stat.st_size as u64,
+    }
+}
+
+fn cvt(value: libc::c_int) -> io::Result<libc::c_int> {
+    if value < 0 {
+        Err(io::Error::last_os_error())
+    } else {
+        Ok(value)
+    }
+}

lib/runtime/src/sys/macos/mod.rs

@@ -0,0 +1,6 @@
+//! macOS backend modules.
+
+pub mod channel;
+pub mod fd;
+pub mod fs;
+pub mod net;

lib/runtime/src/sys/macos/net.rs

@@ -0,0 +1,895 @@
+//! macOS networking backend.
+
+use std::ffi::c_void;
+use std::future::Future;
+use std::io;
+use std::mem::MaybeUninit;
+use std::net::{
+    Ipv4Addr, Ipv6Addr, Shutdown, SocketAddr, SocketAddrV4, SocketAddrV6, ToSocketAddrs,
+};
+use std::os::fd::{AsRawFd, FromRawFd, OwnedFd, RawFd};
+use std::pin::Pin;
+use std::sync::{Arc, Mutex, OnceLock, mpsc};
+use std::thread;
+use std::time::Duration;
+
+use crate::op::completion::completion_for_current_thread;
+use crate::op::net::{AcceptedSocket, NetOp, ReceivedDatagram};
+
+const DEFAULT_LISTENER_BACKLOG: i32 = 1024;
+const DNS_QUEUE_CAPACITY: usize = 256;
+
+type RecvFuture = Pin<Box<dyn Future<Output = io::Result<Vec<u8>>> + 'static>>;
+type SendFuture = Pin<Box<dyn Future<Output = io::Result<usize>> + 'static>>;
+type ShutdownFuture = Pin<Box<dyn Future<Output = io::Result<()>> + 'static>>;
+type BlockingTask = Box<dyn FnOnce() + Send + 'static>;
+
+static DNS_POOL: OnceLock<io::Result<BlockingPool>> = OnceLock::new();
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum ExecutionPath {
+    Kqueue,
+    Offload,
+}
+
+pub fn execution_path(op: &NetOp) -> ExecutionPath {
+    match op {
+        NetOp::Socket { .. }
+        | NetOp::Connect { .. }
+        | NetOp::Bind { .. }
+        | NetOp::Listen { .. }
+        | NetOp::Accept { .. }
+        | NetOp::Send { .. }
+        | NetOp::SendTo { .. }
+        | NetOp::Recv { .. }
+        | NetOp::RecvFrom { .. }
+        | NetOp::Shutdown { .. }
+        | NetOp::Close { .. } => ExecutionPath::Kqueue,
+    }
+}
+
+pub async fn resolve_addrs<A>(addr: A) -> io::Result<Vec<SocketAddr>>
+where
+    A: ToSocketAddrs + Send + 'static,
+{
+    offload(move || {
+        let addrs = addr.to_socket_addrs()?.collect::<Vec<_>>();
+        if addrs.is_empty() {
+            Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "address resolved to no socket addresses",
+            ))
+        } else {
+            Ok(addrs)
+        }
+    })
+    .await
+}
+
+pub async fn socket(op: NetOp) -> io::Result<OwnedFd> {
+    let NetOp::Socket {
+        domain,
+        socket_type,
+        protocol,
+        flags,
+    } = op
+    else {
+        unreachable!("socket backend called with non-socket op");
+    };
+
+    socket_sync(domain, socket_type, protocol, flags)
+}
+
+pub async fn connect(op: NetOp) -> io::Result<()> {
+    let NetOp::Connect { fd, addr } = op else {
+        unreachable!("connect backend called with non-connect op");
+    };
+
+    connect_async(fd, RawSocketAddr::from_socket_addr(addr)).await
+}
+
+pub async fn bind(op: NetOp) -> io::Result<()> {
+    let NetOp::Bind { fd, addr } = op else {
+        unreachable!("bind backend called with non-bind op");
+    };
+
+    bind_sync(fd, RawSocketAddr::from_socket_addr(addr))
+}
+
+pub async fn listen(op: NetOp) -> io::Result<()> {
+    let NetOp::Listen { fd, backlog } = op else {
+        unreachable!("listen backend called with non-listen op");
+    };
+
+    listen_sync(fd, backlog)
+}
+
+pub async fn accept(op: NetOp) -> io::Result<AcceptedSocket> {
+    let NetOp::Accept { fd } = op else {
+        unreachable!("accept backend called with non-accept op");
+    };
+
+    accept_async(fd).await
+}
+
+pub async fn send(op: NetOp) -> io::Result<usize> {
+    let NetOp::Send { fd, data, flags } = op else {
+        unreachable!("send backend called with non-send op");
+    };
+
+    send_async(fd, data, flags).await
+}
+
+pub async fn send_to(op: NetOp) -> io::Result<usize> {
+    let NetOp::SendTo {
+        fd,
+        target,
+        data,
+        flags,
+    } = op
+    else {
+        unreachable!("send_to backend called with non-send_to op");
+    };
+
+    send_to_async(fd, target, data, flags).await
+}
+
+pub async fn recv(op: NetOp) -> io::Result<Vec<u8>> {
+    let NetOp::Recv { fd, len, flags } = op else {
+        unreachable!("recv backend called with non-recv op");
+    };
+
+    recv_async(fd, len, flags).await
+}
+
+pub async fn recv_from(op: NetOp) -> io::Result<ReceivedDatagram> {
+    let NetOp::RecvFrom { fd, len, flags } = op else {
+        unreachable!("recv_from backend called with non-recv_from op");
+    };
+
+    recv_from_async(fd, len, flags).await
+}
+
+pub async fn shutdown(op: NetOp) -> io::Result<()> {
+    let NetOp::Shutdown { fd, how } = op else {
+        unreachable!("shutdown backend called with non-shutdown op");
+    };
+
+    shutdown_sync(fd, how)
+}
+
+pub async fn close(op: NetOp) -> io::Result<()> {
+    let NetOp::Close { fd } = op else {
+        unreachable!("close backend called with non-close op");
+    };
+
+    close_sync(fd)
+}
+
+pub async fn connect_stream(addr: SocketAddr) -> io::Result<OwnedFd> {
+    match connect_stream_inner(addr).await {
+        Err(error) if should_try_ipv4_loopback(addr, &error) => {
+            connect_stream_inner(localhost_v4(addr)).await
+        }
+        result => result,
+    }
+}
+
+pub async fn bind_listener(addr: SocketAddr, backlog: Option<i32>) -> io::Result<OwnedFd> {
+    match bind_listener_inner(addr, backlog).await {
+        Err(error) if should_try_ipv4_loopback(addr, &error) => {
+            bind_listener_inner(localhost_v4(addr), backlog).await
+        }
+        result => result,
+    }
+}
+
+pub async fn bind_datagram(addr: SocketAddr) -> io::Result<OwnedFd> {
+    match bind_datagram_inner(addr).await {
+        Err(error) if should_try_ipv4_loopback(addr, &error) => {
+            bind_datagram_inner(localhost_v4(addr)).await
+        }
+        result => result,
+    }
+}
+
+async fn connect_stream_inner(addr: SocketAddr) -> io::Result<OwnedFd> {
+    let stream = socket(NetOp::Socket {
+        domain: socket_domain(addr),
+        socket_type: libc::SOCK_STREAM,
+        protocol: 0,
+        flags: 0,
+    })
+    .await?;
+
+    connect(NetOp::Connect {
+        fd: stream.as_raw_fd(),
+        addr,
+    })
+    .await?;
+    Ok(stream)
+}
+
+async fn bind_listener_inner(addr: SocketAddr, backlog: Option<i32>) -> io::Result<OwnedFd> {
+    let listener = socket(NetOp::Socket {
+        domain: socket_domain(addr),
+        socket_type: libc::SOCK_STREAM,
+        protocol: 0,
+        flags: 0,
+    })
+    .await?;
+
+    set_reuse_addr(listener.as_raw_fd(), true)?;
+
+    bind(NetOp::Bind {
+        fd: listener.as_raw_fd(),
+        addr,
+    })
+    .await?;
+    listen(NetOp::Listen {
+        fd: listener.as_raw_fd(),
+        backlog: backlog.unwrap_or(DEFAULT_LISTENER_BACKLOG),
+    })
+    .await?;
+    Ok(listener)
+}
+
+async fn bind_datagram_inner(addr: SocketAddr) -> io::Result<OwnedFd> {
+    let socket = socket(NetOp::Socket {
+        domain: socket_domain(addr),
+        socket_type: libc::SOCK_DGRAM,
+        protocol: 0,
+        flags: 0,
+    })
+    .await?;
+
+    bind(NetOp::Bind {
+        fd: socket.as_raw_fd(),
+        addr,
+    })
+    .await?;
+    Ok(socket)
+}
+
+pub async fn duplicate(fd: RawFd) -> io::Result<OwnedFd> {
+    let duplicated = cvt(unsafe { libc::fcntl(fd, libc::F_DUPFD_CLOEXEC, 0) })?;
+    set_nonblocking(duplicated)?;
+    Ok(unsafe { OwnedFd::from_raw_fd(duplicated) })
+}
+
+pub async fn recv_timeout(
+    fd: RawFd,
+    len: usize,
+    flags: i32,
+    timeout: Duration,
+) -> io::Result<Vec<u8>> {
+    io_timeout(timeout, recv_async(fd, len, flags)).await
+}
+
+pub async fn send_timeout(
+    fd: RawFd,
+    data: Vec<u8>,
+    flags: i32,
+    timeout: Duration,
+) -> io::Result<usize> {
+    io_timeout(timeout, send_async(fd, data, flags)).await
+}
+
+pub async fn recv_from_timeout(
+    fd: RawFd,
+    len: usize,
+    flags: i32,
+    timeout: Duration,
+) -> io::Result<ReceivedDatagram> {
+    io_timeout(timeout, recv_from_async(fd, len, flags)).await
+}
+
+pub async fn send_to_timeout(
+    fd: RawFd,
+    data: Vec<u8>,
+    target: SocketAddr,
+    flags: i32,
+    timeout: Duration,
+) -> io::Result<usize> {
+    io_timeout(timeout, send_to_async(fd, target, data, flags)).await
+}
+
+pub async fn connect_stream_timeout(addr: SocketAddr, timeout: Duration) -> io::Result<OwnedFd> {
+    let fd = socket_sync(socket_domain(addr), libc::SOCK_STREAM, 0, 0)?;
+    if let Err(error) = io_timeout(
+        timeout,
+        connect_async(fd.as_raw_fd(), RawSocketAddr::from_socket_addr(addr)),
+    )
+    .await
+    {
+        drop(fd);
+        return Err(error);
+    }
+    Ok(fd)
+}
+
+pub fn local_addr(fd: RawFd) -> io::Result<SocketAddr> {
+    socket_addr_with(libc::getsockname, fd)
+}
+
+pub fn peer_addr(fd: RawFd) -> io::Result<SocketAddr> {
+    socket_addr_with(libc::getpeername, fd)
+}
+
+pub fn nodelay(fd: RawFd) -> io::Result<bool> {
+    let mut value = 0;
+    let mut len = std::mem::size_of::<libc::c_int>() as libc::socklen_t;
+    cvt(unsafe {
+        libc::getsockopt(
+            fd,
+            libc::IPPROTO_TCP,
+            libc::TCP_NODELAY,
+            &mut value as *mut libc::c_int as *mut c_void,
+            &mut len,
+        )
+    })?;
+    Ok(value != 0)
+}
+
+pub fn broadcast(fd: RawFd) -> io::Result<bool> {
+    getsockopt_int(fd, libc::SOL_SOCKET, libc::SO_BROADCAST).map(|value| value != 0)
+}
+
+pub fn set_broadcast(fd: RawFd, enabled: bool) -> io::Result<()> {
+    setsockopt_int(fd, libc::SOL_SOCKET, libc::SO_BROADCAST, enabled.into())
+}
+
+pub fn ttl(fd: RawFd) -> io::Result<u32> {
+    match socket_family(fd)? {
+        libc::AF_INET => {
+            getsockopt_int(fd, libc::IPPROTO_IP, libc::IP_TTL).map(|value| value as u32)
+        }
+        libc::AF_INET6 => getsockopt_int(fd, libc::IPPROTO_IPV6, libc::IPV6_UNICAST_HOPS)
+            .map(|value| value as u32),
+        family => Err(io::Error::new(
+            io::ErrorKind::InvalidInput,
+            format!("unsupported socket family {family} for TTL"),
+        )),
+    }
+}
+
+pub fn set_ttl(fd: RawFd, ttl: u32) -> io::Result<()> {
+    let ttl = i32::try_from(ttl)
+        .map_err(|_| io::Error::new(io::ErrorKind::InvalidInput, "TTL exceeds i32 range"))?;
+    match socket_family(fd)? {
+        libc::AF_INET => setsockopt_int(fd, libc::IPPROTO_IP, libc::IP_TTL, ttl),
+        libc::AF_INET6 => setsockopt_int(fd, libc::IPPROTO_IPV6, libc::IPV6_UNICAST_HOPS, ttl),
+        family => Err(io::Error::new(
+            io::ErrorKind::InvalidInput,
+            format!("unsupported socket family {family} for TTL"),
+        )),
+    }
+}
+
+pub fn set_nodelay(fd: RawFd, enabled: bool) -> io::Result<()> {
+    let value: libc::c_int = enabled.into();
+    cvt(unsafe {
+        libc::setsockopt(
+            fd,
+            libc::IPPROTO_TCP,
+            libc::TCP_NODELAY,
+            &value as *const libc::c_int as *const c_void,
+            std::mem::size_of_val(&value) as libc::socklen_t,
+        )
+    })
+    .map(|_| ())
+}
+
+pub fn recv_future(fd: RawFd, len: usize) -> RecvFuture {
+    Box::pin(recv(NetOp::Recv { fd, len, flags: 0 }))
+}
+
+pub fn send_future(fd: RawFd, data: Vec<u8>) -> SendFuture {
+    Box::pin(send(NetOp::Send { fd, data, flags: 0 }))
+}
+
+pub fn shutdown_future(fd: RawFd, how: Shutdown) -> ShutdownFuture {
+    Box::pin(shutdown(NetOp::Shutdown { fd, how }))
+}
+
+async fn offload<T: Send + 'static>(
+    work: impl FnOnce() -> io::Result<T> + Send + 'static,
+) -> io::Result<T> {
+    let (future, handle) = completion_for_current_thread::<io::Result<T>>();
+    if let Err(error) = dns_pool().and_then(|pool| {
+        pool.spawn(Box::new({
+            let handle = handle.clone();
+            move || handle.complete(work())
+        }))
+    }) {
+        handle.complete(Err(error));
+    }
+    future.await
+}
+
+struct BlockingPool {
+    sender: mpsc::SyncSender<BlockingTask>,
+}
+
+impl BlockingPool {
+    fn spawn(&self, task: BlockingTask) -> io::Result<()> {
+        self.sender.try_send(task).map_err(|error| match error {
+            mpsc::TrySendError::Full(_) => io::Error::new(
+                io::ErrorKind::WouldBlock,
+                "DNS resolver blocking worker queue is full",
+            ),
+            mpsc::TrySendError::Disconnected(_) => io::Error::new(
+                io::ErrorKind::BrokenPipe,
+                "DNS resolver blocking worker pool has stopped",
+            ),
+        })
+    }
+}
+
+fn dns_pool() -> io::Result<&'static BlockingPool> {
+    match DNS_POOL.get_or_init(create_dns_pool) {
+        Ok(pool) => Ok(pool),
+        Err(error) => Err(io::Error::new(error.kind(), error.to_string())),
+    }
+}
+
+fn create_dns_pool() -> io::Result<BlockingPool> {
+    let (sender, receiver) = mpsc::sync_channel::<BlockingTask>(DNS_QUEUE_CAPACITY);
+    let receiver = Arc::new(Mutex::new(receiver));
+    let worker_count = std::thread::available_parallelism()
+        .map(usize::from)
+        .unwrap_or(2)
+        .clamp(2, 4);
+    let mut spawned = 0usize;
+    let mut last_error = None;
+
+    for index in 0..worker_count {
+        let receiver = Arc::clone(&receiver);
+        match thread::Builder::new()
+            .name(format!("ruin-runtime-dns-{index}"))
+            .spawn(move || {
+                loop {
+                    let task = {
+                        let receiver = receiver.lock().expect("DNS worker queue mutex poisoned");
+                        receiver.recv()
+                    };
+                    match task {
+                        Ok(task) => task(),
+                        Err(_) => break,
+                    }
+                }
+            }) {
+            Ok(_) => spawned += 1,
+            Err(error) => last_error = Some(error),
+        }
+    }
+
+    if spawned == 0 {
+        return Err(io::Error::other(last_error.expect(
+            "at least one DNS worker spawn should have been attempted",
+        )));
+    }
+
+    Ok(BlockingPool { sender })
+}
+
+async fn io_timeout<T>(
+    timeout: Duration,
+    future: impl Future<Output = io::Result<T>>,
+) -> io::Result<T> {
+    crate::time::timeout(timeout, future)
+        .await
+        .map_err(|_| io::Error::new(io::ErrorKind::TimedOut, "operation timed out"))?
+}
+
+fn socket_domain(addr: SocketAddr) -> i32 {
+    match addr {
+        SocketAddr::V4(_) => libc::AF_INET,
+        SocketAddr::V6(_) => libc::AF_INET6,
+    }
+}
+
+fn shutdown_how(how: Shutdown) -> i32 {
+    match how {
+        Shutdown::Read => libc::SHUT_RD,
+        Shutdown::Write => libc::SHUT_WR,
+        Shutdown::Both => libc::SHUT_RDWR,
+    }
+}
+
+fn socket_addr_with(
+    op: unsafe extern "C" fn(RawFd, *mut libc::sockaddr, *mut libc::socklen_t) -> libc::c_int,
+    fd: RawFd,
+) -> io::Result<SocketAddr> {
+    let mut storage = MaybeUninit::<libc::sockaddr_storage>::zeroed();
+    let mut len = std::mem::size_of::<libc::sockaddr_storage>() as libc::socklen_t;
+    cvt(unsafe { op(fd, storage.as_mut_ptr().cast::<libc::sockaddr>(), &mut len) })?;
+    let storage = unsafe { storage.assume_init() };
+    socket_addr_from_storage(&storage, len)
+}
+
+fn set_reuse_addr(fd: RawFd, enabled: bool) -> io::Result<()> {
+    setsockopt_int(fd, libc::SOL_SOCKET, libc::SO_REUSEADDR, enabled.into())
+}
+
+fn socket_family(fd: RawFd) -> io::Result<i32> {
+    let mut storage = MaybeUninit::<libc::sockaddr_storage>::zeroed();
+    let mut len = std::mem::size_of::<libc::sockaddr_storage>() as libc::socklen_t;
+    cvt(unsafe { libc::getsockname(fd, storage.as_mut_ptr().cast::<libc::sockaddr>(), &mut len) })?;
+    let storage = unsafe { storage.assume_init() };
+    Ok(storage.ss_family as i32)
+}
+
+fn getsockopt_int(fd: RawFd, level: i32, name: i32) -> io::Result<i32> {
+    let mut value = 0;
+    let mut len = std::mem::size_of::<libc::c_int>() as libc::socklen_t;
+    cvt(unsafe {
+        libc::getsockopt(
+            fd,
+            level,
+            name,
+            &mut value as *mut libc::c_int as *mut c_void,
+            &mut len,
+        )
+    })?;
+    Ok(value)
+}
+
+fn setsockopt_int(fd: RawFd, level: i32, name: i32, value: i32) -> io::Result<()> {
+    cvt(unsafe {
+        libc::setsockopt(
+            fd,
+            level,
+            name,
+            &value as *const libc::c_int as *const c_void,
+            std::mem::size_of_val(&value) as libc::socklen_t,
+        )
+    })
+    .map(|_| ())
+}
+
+fn socket_addr_from_storage(
+    storage: &libc::sockaddr_storage,
+    len: libc::socklen_t,
+) -> io::Result<SocketAddr> {
+    match storage.ss_family as i32 {
+        libc::AF_INET => {
+            if len < std::mem::size_of::<libc::sockaddr_in>() as libc::socklen_t {
+                return Err(io::Error::new(
+                    io::ErrorKind::InvalidData,
+                    "sockaddr_in length is truncated",
+                ));
+            }
+            let addr = unsafe { *(storage as *const _ as *const libc::sockaddr_in) };
+            Ok(SocketAddr::V4(SocketAddrV4::new(
+                Ipv4Addr::from(u32::from_be(addr.sin_addr.s_addr)),
+                u16::from_be(addr.sin_port),
+            )))
+        }
+        libc::AF_INET6 => {
+            if len < std::mem::size_of::<libc::sockaddr_in6>() as libc::socklen_t {
+                return Err(io::Error::new(
+                    io::ErrorKind::InvalidData,
+                    "sockaddr_in6 length is truncated",
+                ));
+            }
+            let addr = unsafe { *(storage as *const _ as *const libc::sockaddr_in6) };
+            Ok(SocketAddr::V6(SocketAddrV6::new(
+                Ipv6Addr::from(addr.sin6_addr.s6_addr),
+                u16::from_be(addr.sin6_port),
+                addr.sin6_flowinfo,
+                addr.sin6_scope_id,
+            )))
+        }
+        family => Err(io::Error::new(
+            io::ErrorKind::InvalidData,
+            format!("unsupported socket family {family}"),
+        )),
+    }
+}
+
+#[derive(Clone, Copy)]
+struct RawSocketAddr {
+    storage: libc::sockaddr_storage,
+    len: libc::socklen_t,
+}
+
+impl RawSocketAddr {
+    fn from_socket_addr(addr: SocketAddr) -> Self {
+        match addr {
+            SocketAddr::V4(addr) => {
+                let sockaddr = libc::sockaddr_in {
+                    sin_len: std::mem::size_of::<libc::sockaddr_in>() as u8,
+                    sin_family: libc::AF_INET as libc::sa_family_t,
+                    sin_port: addr.port().to_be(),
+                    sin_addr: libc::in_addr {
+                        s_addr: u32::from_be_bytes(addr.ip().octets()).to_be(),
+                    },
+                    sin_zero: [0; 8],
+                };
+                let mut storage =
+                    unsafe { MaybeUninit::<libc::sockaddr_storage>::zeroed().assume_init() };
+                unsafe {
+                    std::ptr::write(
+                        &mut storage as *mut libc::sockaddr_storage as *mut libc::sockaddr_in,
+                        sockaddr,
+                    );
+                }
+                Self {
+                    storage,
+                    len: std::mem::size_of::<libc::sockaddr_in>() as libc::socklen_t,
+                }
+            }
+            SocketAddr::V6(addr) => {
+                let sockaddr = libc::sockaddr_in6 {
+                    sin6_len: std::mem::size_of::<libc::sockaddr_in6>() as u8,
+                    sin6_family: libc::AF_INET6 as libc::sa_family_t,
+                    sin6_port: addr.port().to_be(),
+                    sin6_flowinfo: addr.flowinfo(),
+                    sin6_addr: libc::in6_addr {
+                        s6_addr: addr.ip().octets(),
+                    },
+                    sin6_scope_id: addr.scope_id(),
+                };
+                let mut storage =
+                    unsafe { MaybeUninit::<libc::sockaddr_storage>::zeroed().assume_init() };
+                unsafe {
+                    std::ptr::write(
+                        &mut storage as *mut libc::sockaddr_storage as *mut libc::sockaddr_in6,
+                        sockaddr,
+                    );
+                }
+                Self {
+                    storage,
+                    len: std::mem::size_of::<libc::sockaddr_in6>() as libc::socklen_t,
+                }
+            }
+        }
+    }
+
+    fn as_ptr(&self) -> *const libc::sockaddr {
+        &self.storage as *const libc::sockaddr_storage as *const libc::sockaddr
+    }
+
+    fn len(&self) -> libc::socklen_t {
+        self.len
+    }
+}
+
+fn socket_sync(domain: i32, socket_type: i32, protocol: i32, _flags: u32) -> io::Result<OwnedFd> {
+    let fd = cvt(unsafe { libc::socket(domain, socket_type, protocol) })?;
+    set_cloexec(fd)?;
+    set_nonblocking(fd)?;
+    Ok(unsafe { OwnedFd::from_raw_fd(fd) })
+}
+
+async fn connect_async(fd: RawFd, addr: RawSocketAddr) -> io::Result<()> {
+    loop {
+        let result = unsafe { libc::connect(fd, addr.as_ptr(), addr.len()) };
+        if result == 0 {
+            return Ok(());
+        }
+
+        let error = io::Error::last_os_error();
+        match error.raw_os_error() {
+            Some(libc::EINTR) => continue,
+            Some(libc::EINPROGRESS) | Some(libc::EALREADY) => {
+                crate::sys::current::fd::wait_writable(fd).await?;
+                return socket_error(fd);
+            }
+            Some(libc::EISCONN) => return Ok(()),
+            _ => return Err(error),
+        }
+    }
+}
+
+fn bind_sync(fd: RawFd, addr: RawSocketAddr) -> io::Result<()> {
+    cvt(unsafe { libc::bind(fd, addr.as_ptr(), addr.len()) }).map(|_| ())
+}
+
+fn listen_sync(fd: RawFd, backlog: i32) -> io::Result<()> {
+    cvt(unsafe { libc::listen(fd, backlog) }).map(|_| ())
+}
+
+fn accept_sync(fd: RawFd) -> io::Result<AcceptedSocket> {
+    let mut storage = MaybeUninit::<libc::sockaddr_storage>::zeroed();
+    let mut len = std::mem::size_of::<libc::sockaddr_storage>() as libc::socklen_t;
+    let accepted_fd =
+        cvt(unsafe { libc::accept(fd, storage.as_mut_ptr().cast::<libc::sockaddr>(), &mut len) })?;
+    set_cloexec(accepted_fd)?;
+    let storage = unsafe { storage.assume_init() };
+    let peer_addr = socket_addr_from_storage(&storage, len)?;
+    Ok(AcceptedSocket {
+        fd: accepted_fd,
+        peer_addr,
+    })
+}
+
+async fn accept_async(fd: RawFd) -> io::Result<AcceptedSocket> {
+    loop {
+        match accept_sync(fd) {
+            Ok(socket) => {
+                set_nonblocking(socket.fd)?;
+                return Ok(socket);
+            }
+            Err(error) if error.kind() == io::ErrorKind::WouldBlock => {
+                crate::sys::current::fd::wait_readable(fd).await?;
+            }
+            Err(error) if error.kind() == io::ErrorKind::Interrupted => {}
+            Err(error) => return Err(error),
+        }
+    }
+}
+
+async fn send_async(fd: RawFd, data: Vec<u8>, flags: i32) -> io::Result<usize> {
+    loop {
+        match send_slice_sync(fd, &data, flags) {
+            Ok(written) => return Ok(written),
+            Err(error) if error.kind() == io::ErrorKind::WouldBlock => {
+                crate::sys::current::fd::wait_writable(fd).await?;
+            }
+            Err(error) if error.kind() == io::ErrorKind::Interrupted => {}
+            Err(error) => return Err(error),
+        }
+    }
+}
+
+fn send_slice_sync(fd: RawFd, data: &[u8], flags: i32) -> io::Result<usize> {
+    let written = unsafe { libc::send(fd, data.as_ptr().cast::<c_void>(), data.len(), flags) };
+    cvt_long(written).map(|written| written as usize)
+}
+
+async fn send_to_async(
+    fd: RawFd,
+    target: SocketAddr,
+    data: Vec<u8>,
+    flags: i32,
+) -> io::Result<usize> {
+    loop {
+        match send_to_slice_sync(fd, target, &data, flags) {
+            Ok(written) => return Ok(written),
+            Err(error) if error.kind() == io::ErrorKind::WouldBlock => {
+                crate::sys::current::fd::wait_writable(fd).await?;
+            }
+            Err(error) if error.kind() == io::ErrorKind::Interrupted => {}
+            Err(error) => return Err(error),
+        }
+    }
+}
+
+fn send_to_slice_sync(fd: RawFd, target: SocketAddr, data: &[u8], flags: i32) -> io::Result<usize> {
+    let addr = RawSocketAddr::from_socket_addr(target);
+    let written = unsafe {
+        libc::sendto(
+            fd,
+            data.as_ptr().cast::<c_void>(),
+            data.len(),
+            flags,
+            addr.as_ptr(),
+            addr.len(),
+        )
+    };
+    cvt_long(written).map(|written| written as usize)
+}
+
+async fn recv_async(fd: RawFd, len: usize, flags: i32) -> io::Result<Vec<u8>> {
+    loop {
+        match recv_sync(fd, len, flags) {
+            Ok(data) => return Ok(data),
+            Err(error) if error.kind() == io::ErrorKind::WouldBlock => {
+                crate::sys::current::fd::wait_readable(fd).await?;
+            }
+            Err(error) if error.kind() == io::ErrorKind::Interrupted => {}
+            Err(error) => return Err(error),
+        }
+    }
+}
+
+fn recv_sync(fd: RawFd, len: usize, flags: i32) -> io::Result<Vec<u8>> {
+    let mut data = vec![0u8; len];
+    let read = unsafe { libc::recv(fd, data.as_mut_ptr().cast::<c_void>(), len, flags) };
+    let read = cvt_long(read)? as usize;
+    data.truncate(read);
+    Ok(data)
+}
+
+async fn recv_from_async(fd: RawFd, len: usize, flags: i32) -> io::Result<ReceivedDatagram> {
+    loop {
+        match recv_from_sync(fd, len, flags) {
+            Ok(datagram) => return Ok(datagram),
+            Err(error) if error.kind() == io::ErrorKind::WouldBlock => {
+                crate::sys::current::fd::wait_readable(fd).await?;
+            }
+            Err(error) if error.kind() == io::ErrorKind::Interrupted => {}
+            Err(error) => return Err(error),
+        }
+    }
+}
+
+fn recv_from_sync(fd: RawFd, len: usize, flags: i32) -> io::Result<ReceivedDatagram> {
+    let mut data = vec![0u8; len];
+    let mut storage = MaybeUninit::<libc::sockaddr_storage>::zeroed();
+    let mut addr_len = std::mem::size_of::<libc::sockaddr_storage>() as libc::socklen_t;
+    let read = unsafe {
+        libc::recvfrom(
+            fd,
+            data.as_mut_ptr().cast::<c_void>(),
+            len,
+            flags,
+            storage.as_mut_ptr().cast::<libc::sockaddr>(),
+            &mut addr_len,
+        )
+    };
+    let read = cvt_long(read)? as usize;
+    data.truncate(read);
+    let storage = unsafe { storage.assume_init() };
+    let peer_addr = socket_addr_from_storage(&storage, addr_len)?;
+    Ok(ReceivedDatagram { data, peer_addr })
+}
+
+fn shutdown_sync(fd: RawFd, how: Shutdown) -> io::Result<()> {
+    cvt(unsafe { libc::shutdown(fd, shutdown_how(how)) }).map(|_| ())
+}
+
+fn close_sync(fd: RawFd) -> io::Result<()> {
+    cvt(unsafe { libc::close(fd) }).map(|_| ())
+}
+
+fn set_cloexec(fd: RawFd) -> io::Result<()> {
+    let flags = cvt(unsafe { libc::fcntl(fd, libc::F_GETFD) })?;
+    cvt(unsafe { libc::fcntl(fd, libc::F_SETFD, flags | libc::FD_CLOEXEC) })?;
+    Ok(())
+}
+
+fn set_nonblocking(fd: RawFd) -> io::Result<()> {
+    let flags = cvt(unsafe { libc::fcntl(fd, libc::F_GETFL) })?;
+    cvt(unsafe { libc::fcntl(fd, libc::F_SETFL, flags | libc::O_NONBLOCK) })?;
+    Ok(())
+}
+
+fn should_try_ipv4_loopback(addr: SocketAddr, error: &io::Error) -> bool {
+    matches!(addr, SocketAddr::V6(v6) if v6.ip().is_loopback())
+        && matches!(
+            error.raw_os_error(),
+            Some(libc::EADDRNOTAVAIL | libc::EAFNOSUPPORT | libc::ENETUNREACH)
+        )
+}
+
+fn socket_error(fd: RawFd) -> io::Result<()> {
+    let mut so_error: libc::c_int = 0;
+    let mut len = std::mem::size_of::<libc::c_int>() as libc::socklen_t;
+    cvt(unsafe {
+        libc::getsockopt(
+            fd,
+            libc::SOL_SOCKET,
+            libc::SO_ERROR,
+            &mut so_error as *mut libc::c_int as *mut c_void,
+            &mut len,
+        )
+    })?;
+    if so_error == 0 {
+        Ok(())
+    } else {
+        Err(io::Error::from_raw_os_error(so_error))
+    }
+}
+
+fn localhost_v4(addr: SocketAddr) -> SocketAddr {
+    SocketAddr::V4(SocketAddrV4::new(Ipv4Addr::LOCALHOST, addr.port()))
+}
+
+fn cvt(value: libc::c_int) -> io::Result<libc::c_int> {
+    if value < 0 {
+        Err(io::Error::last_os_error())
+    } else {
+        Ok(value)
+    }
+}
+
+fn cvt_long(value: libc::ssize_t) -> io::Result<libc::ssize_t> {
+    if value < 0 {
+        Err(io::Error::last_os_error())
+    } else {
+        Ok(value)
+    }
+}

lib/runtime/src/sys/mod.rs

@@ -2,3 +2,10 @@
 
 #[cfg(all(target_os = "linux", target_arch = "x86_64"))]
 pub mod linux;
+#[cfg(all(target_os = "macos", target_arch = "aarch64"))]
+pub mod macos;
+
+#[cfg(all(target_os = "linux", target_arch = "x86_64"))]
+pub use linux as current;
+#[cfg(all(target_os = "macos", target_arch = "aarch64"))]
+pub use macos as current;

lib/ui/benches/layout_bench.rs

@@ -67,7 +67,9 @@ fn bench_scroll_list(c: &mut Criterion) {
     let viewport_height = 640.0;
     let n = 500;
 
-    let mut scroll_box = Element::scroll_box(0.0).width(400.0).height(viewport_height);
+    let mut scroll_box = Element::scroll_box(0.0)
+        .width(400.0)
+        .height(viewport_height);
     for i in 0..n {
         scroll_box = scroll_box.child(
             Element::new()
@@ -90,5 +92,10 @@ fn bench_scroll_list(c: &mut Criterion) {
     });
 }
 
-criterion_group!(benches, bench_static_tree, bench_single_change, bench_scroll_list);
+criterion_group!(
+    benches,
+    bench_static_tree,
+    bench_single_change,
+    bench_scroll_list
+);
 criterion_main!(benches);

lib/ui/examples/explicit_ui_prototype.rs

@@ -107,6 +107,7 @@ fn log_platform_event(event: &PlatformEvent) {
                 "clipboard text received"
             );
         }
+        #[cfg(target_os = "linux")]
         PlatformEvent::PrimarySelectionText { window_id, text } => {
             tracing::debug!(
                 event = "primary_selection_text",

lib/ui/src/layout.rs

@@ -7,7 +7,10 @@ use crate::scene::{
     UiSize,
 };
 use crate::text::TextSystem;
-use crate::tree::{AlignItems, CursorIcon, Edges, Element, ElementId, FlexDirection, ImageNode, Style};
+use crate::tree::{
+    AlignItems, CursorIcon, Edges, Element, ElementId, FlexDirection, ImageNode, JustifyContent,
+    Style,
+};
 
 pub fn layout_scene(version: u64, logical_size: UiSize, root: &Element) -> SceneSnapshot {
     let mut text_system = TextSystem::new();
@@ -34,6 +37,35 @@ pub struct LayoutSnapshot {
     pub root_min_size: UiSize,
 }
 
+#[derive(Clone, Copy, Debug, Default, PartialEq)]
+pub struct LayoutFrameStats {
+    pub total_ms: f64,
+    pub nodes: usize,
+    pub text_nodes: usize,
+    pub container_nodes: usize,
+    pub background_quads: usize,
+    pub intrinsic_calls: usize,
+    pub intrinsic_size_calls: usize,
+    pub intrinsic_text_calls: usize,
+    pub intrinsic_container_calls: usize,
+    pub intrinsic_ms: f64,
+    pub text_prepare_calls: usize,
+    pub text_prepare_ms: f64,
+    pub viewport_culled: usize,
+    pub layout_cache_hits: usize,
+    pub layout_cache_misses: usize,
+    pub intrinsic_cache_hits: usize,
+    pub text_requests: u32,
+    pub text_cache_hits: u32,
+    pub text_cache_misses: u32,
+    pub text_output_glyphs: u32,
+    pub text_family_resolve_ms: f64,
+    pub text_buffer_build_ms: f64,
+    pub text_glyph_collect_ms: f64,
+    pub text_miss_ms: f64,
+    pub scene_items: usize,
+}
+
 #[derive(Clone, Debug, Eq, Hash, PartialEq)]
 pub struct LayoutPath(Vec<u32>);
 
@@ -192,6 +224,16 @@ pub fn layout_snapshot_with_cache(
     text_system: &mut TextSystem,
     layout_cache: &mut LayoutCache,
 ) -> LayoutSnapshot {
+    layout_snapshot_with_cache_and_stats(version, logical_size, root, text_system, layout_cache).0
+}
+
+pub fn layout_snapshot_with_cache_and_stats(
+    version: u64,
+    logical_size: UiSize,
+    root: &Element,
+    text_system: &mut TextSystem,
+    layout_cache: &mut LayoutCache,
+) -> (LayoutSnapshot, LayoutFrameStats) {
     let layout_started = Instant::now();
     let perf_enabled = tracing::enabled!(target: "ruin_ui::layout_perf", tracing::Level::DEBUG);
     let mut perf_stats = LayoutPerfStats::new(perf_enabled);
@@ -213,48 +255,78 @@ pub fn layout_snapshot_with_cache(
         None,
     );
     let text_stats = text_system.take_frame_stats();
+    let stats = LayoutFrameStats {
+        total_ms: layout_started.elapsed().as_secs_f64() * 1_000.0,
+        nodes: perf_stats.nodes,
+        text_nodes: perf_stats.text_nodes,
+        container_nodes: perf_stats.container_nodes,
+        background_quads: perf_stats.background_quads,
+        intrinsic_calls: perf_stats.intrinsic_calls,
+        intrinsic_size_calls: perf_stats.intrinsic_size_calls,
+        intrinsic_text_calls: perf_stats.intrinsic_text_calls,
+        intrinsic_container_calls: perf_stats.intrinsic_container_calls,
+        intrinsic_ms: perf_stats.intrinsic_ms,
+        text_prepare_calls: perf_stats.text_prepare_calls,
+        text_prepare_ms: perf_stats.text_prepare_ms,
+        viewport_culled: perf_stats.viewport_culled,
+        layout_cache_hits: perf_stats.layout_cache_hits,
+        layout_cache_misses: perf_stats.layout_cache_misses,
+        intrinsic_cache_hits: perf_stats.intrinsic_cache_hits,
+        text_requests: text_stats.requests,
+        text_cache_hits: text_stats.cache_hits,
+        text_cache_misses: text_stats.cache_misses,
+        text_output_glyphs: text_stats.output_glyphs,
+        text_family_resolve_ms: text_stats.family_resolve_ms,
+        text_buffer_build_ms: text_stats.buffer_build_ms,
+        text_glyph_collect_ms: text_stats.glyph_collect_ms,
+        text_miss_ms: text_stats.miss_ms,
+        scene_items: scene.items.len(),
+    };
     if perf_stats.enabled {
         tracing::debug!(
             target: "ruin_ui::layout_perf",
             scene_version = version,
             width = logical_size.width,
             height = logical_size.height,
-            total_ms = layout_started.elapsed().as_secs_f64() * 1_000.0,
+            total_ms = stats.total_ms,
-            nodes = perf_stats.nodes,
+            nodes = stats.nodes,
-            text_nodes = perf_stats.text_nodes,
+            text_nodes = stats.text_nodes,
-            container_nodes = perf_stats.container_nodes,
+            container_nodes = stats.container_nodes,
-            background_quads = perf_stats.background_quads,
+            background_quads = stats.background_quads,
-            intrinsic_calls = perf_stats.intrinsic_calls,
+            intrinsic_calls = stats.intrinsic_calls,
-            intrinsic_size_calls = perf_stats.intrinsic_size_calls,
+            intrinsic_size_calls = stats.intrinsic_size_calls,
-            intrinsic_text_calls = perf_stats.intrinsic_text_calls,
+            intrinsic_text_calls = stats.intrinsic_text_calls,
-            intrinsic_container_calls = perf_stats.intrinsic_container_calls,
+            intrinsic_container_calls = stats.intrinsic_container_calls,
-            intrinsic_ms = perf_stats.intrinsic_ms,
+            intrinsic_ms = stats.intrinsic_ms,
-            text_prepare_calls = perf_stats.text_prepare_calls,
+            text_prepare_calls = stats.text_prepare_calls,
-            text_prepare_ms = perf_stats.text_prepare_ms,
+            text_prepare_ms = stats.text_prepare_ms,
-            viewport_culled = perf_stats.viewport_culled,
+            viewport_culled = stats.viewport_culled,
-            layout_cache_hits = perf_stats.layout_cache_hits,
+            layout_cache_hits = stats.layout_cache_hits,
-            layout_cache_misses = perf_stats.layout_cache_misses,
+            layout_cache_misses = stats.layout_cache_misses,
-            intrinsic_cache_hits = perf_stats.intrinsic_cache_hits,
+            intrinsic_cache_hits = stats.intrinsic_cache_hits,
-            text_requests = text_stats.requests,
+            text_requests = stats.text_requests,
-            text_cache_hits = text_stats.cache_hits,
+            text_cache_hits = stats.text_cache_hits,
-            text_cache_misses = text_stats.cache_misses,
+            text_cache_misses = stats.text_cache_misses,
-            text_output_glyphs = text_stats.output_glyphs,
+            text_output_glyphs = stats.text_output_glyphs,
-            text_family_resolve_ms = text_stats.family_resolve_ms,
+            text_family_resolve_ms = stats.text_family_resolve_ms,
-            text_buffer_build_ms = text_stats.buffer_build_ms,
+            text_buffer_build_ms = stats.text_buffer_build_ms,
-            text_glyph_collect_ms = text_stats.glyph_collect_ms,
+            text_glyph_collect_ms = stats.text_glyph_collect_ms,
-            text_miss_ms = text_stats.miss_ms,
+            text_miss_ms = stats.text_miss_ms,
-            scene_items = scene.items.len(),
+            scene_items = stats.scene_items,
             "layout snapshot perf"
         );
     }
     let root_min_size = element_min_size(root);
-    LayoutSnapshot {
+    (
-        scene,
+        LayoutSnapshot {
-        interaction_tree: InteractionTree {
+            scene,
-            root: interaction_root,
+            interaction_tree: InteractionTree {
+                root: interaction_root,
+            },
+            root_min_size,
         },
-        root_min_size,
+        stats,
-    }
+    )
 }
 
 #[allow(clippy::too_many_arguments)]
@@ -278,20 +350,14 @@ fn layout_element(
         && !rects_overlap(rect, clip)
     {
         perf_stats.viewport_culled += 1;
-        return LayoutNode {
+        return layout_interaction_skeleton(
-            path,
+            element,
-            element_id: element.id,
             rect,
-            corner_radius: 0.0,
+            path,
-            clip_rect: None,
+            text_system,
-            pointer_events: element.style.pointer_events,
+            perf_stats,
-            focusable: element.style.focusable,
+            layout_cache,
-            cursor: element.style.cursor.unwrap_or(CursorIcon::Default),
+        );
-            scroll_metrics: None,
-            prepared_image: None,
-            prepared_text: None,
-            children: Vec::new(),
-        };
     }
 
     // Incremental layout cache check.
@@ -303,6 +369,7 @@ fn layout_element(
         subtree_hash,
         avail_width_bits: rect.size.width.round() as u32,
         avail_height_bits: rect.size.height.round() as u32,
+        clip_rect_bits: cache_clip_rect_bits(rect, clip_rect),
     };
     if let Some(cached) = layout_cache.results.get(&cache_key) {
         let offset = rect.origin;
@@ -586,13 +653,7 @@ fn layout_element(
         text_system,
         perf_stats,
         layout_cache,
-        // Do NOT propagate clip_rect into children: the scroll-box PushClip already clips
+        clip_rect,
-        // them visually, and propagating the clip causes the layout cache to bake in
-        // culling results for a specific scroll position.  When the scroll changes, the
-        // same cache entry would replay with stale "empty" children that were culled at
-        // the previous offset.  Culling applies only at the direct-child level of the
-        // scroll box (which passes Some(viewport_rect) to layout_container_children).
-        None,
     );
 
     if pushed_clip {
@@ -879,25 +940,23 @@ fn layout_container_children(
         // children with no explicit cross-axis style, since flex main size is unknown here.
         // align_self on the child overrides the parent's align_items for this child.
         let effective_align = child.style.align_self.unwrap_or(element.style.align_items);
-        let natural_cross =
+        let natural_cross = if effective_align != AlignItems::Stretch
-            if effective_align != AlignItems::Stretch
+            && !is_flex
-                && !is_flex
+            && child_cross_size(child, element.style.direction).is_none()
-                && child_cross_size(child, element.style.direction).is_none()
+        {
-            {
+            let offered = match element.style.direction {
-                let offered = match element.style.direction {
+                FlexDirection::Row => UiSize::new(measured_main, available_cross),
-                    FlexDirection::Row => UiSize::new(measured_main, available_cross),
+                FlexDirection::Column => UiSize::new(available_cross, measured_main),
-                    FlexDirection::Column => UiSize::new(available_cross, measured_main),
-                };
-                let natural =
-                    intrinsic_size(child, offered, text_system, perf_stats, layout_cache);
-                Some(
-                    cross_axis_size(natural, element.style.direction)
-                        .max(min_cross_outer)
-                        .min(available_cross.max(min_cross_outer)),
-                )
-            } else {
-                None
             };
+            let natural = intrinsic_size(child, offered, text_system, perf_stats, layout_cache);
+            Some(
+                cross_axis_size(natural, element.style.direction)
+                    .max(min_cross_outer)
+                    .min(available_cross.max(min_cross_outer)),
+            )
+        } else {
+            None
+        };
 
         if is_flex {
             flex_total += child_flex_weight(child);
@@ -913,7 +972,13 @@ fn layout_container_children(
     }
 
     let remaining_main = (available_main - fixed_total).max(0.0);
-    let mut cursor = main_axis_origin(content, element.style.direction);
+    let free_space = if flex_total > 0.0 { 0.0 } else { remaining_main };
+    let justify = justify_offsets(
+        element.style.justify_content,
+        free_space,
+        element.children.len(),
+    );
+    let mut cursor = main_axis_origin(content, element.style.direction) + justify.leading;
     let mut children = Vec::with_capacity(element.children.len());
     for (index, (child, measured)) in element.children.iter().zip(measured_children).enumerate() {
         let child_main = if measured.is_flex {
@@ -961,7 +1026,263 @@ fn layout_container_children(
             layout_cache,
             clip_rect,
         ));
-        cursor += child_main.max(0.0) + element.style.gap;
+        cursor += child_main.max(0.0) + element.style.gap + justify.between;
+    }
+    children
+}
+
+fn layout_interaction_skeleton(
+    element: &Element,
+    rect: Rect,
+    path: LayoutPath,
+    text_system: &mut TextSystem,
+    perf_stats: &mut LayoutPerfStats,
+    layout_cache: &mut LayoutCache,
+) -> LayoutNode {
+    let cursor = element.style.cursor.unwrap_or_else(|| {
+        if element.text_node().is_some() {
+            CursorIcon::Text
+        } else {
+            CursorIcon::Default
+        }
+    });
+    let mut interaction = LayoutNode {
+        path,
+        element_id: element.id,
+        rect,
+        corner_radius: uniform_corner_radius(&element.style, rect),
+        clip_rect: None,
+        pointer_events: element.style.pointer_events,
+        focusable: element.style.focusable,
+        cursor,
+        scroll_metrics: None,
+        prepared_image: None,
+        prepared_text: None,
+        children: Vec::new(),
+    };
+
+    if rect.size.width <= 0.0 || rect.size.height <= 0.0 {
+        return interaction;
+    }
+
+    if let Some(scroll_box) = element.scroll_box_node() {
+        let content = inset_rect(rect, content_insets(&element.style));
+        if content.size.width <= 0.0 || content.size.height <= 0.0 {
+            return interaction;
+        }
+        let gutter_width = scroll_box
+            .scrollbar
+            .gutter_width
+            .max(0.0)
+            .min(content.size.width);
+        let viewport_rect = Rect::new(
+            content.origin.x,
+            content.origin.y,
+            (content.size.width - gutter_width).max(0.0),
+            content.size.height,
+        );
+        interaction.clip_rect = Some(viewport_rect);
+        let content_size = intrinsic_container_content_size(
+            element,
+            UiSize::new(
+                viewport_rect.size.width.max(0.0),
+                viewport_rect.size.height.max(0.0),
+            ),
+            text_system,
+            perf_stats,
+            layout_cache,
+        );
+        let content_height = content_size.height.max(viewport_rect.size.height);
+        let offset_y = scroll_box
+            .offset_y
+            .max(0.0)
+            .min((content_height - viewport_rect.size.height).max(0.0));
+        interaction.children = layout_interaction_skeleton_children(
+            element,
+            Rect::new(
+                viewport_rect.origin.x,
+                viewport_rect.origin.y - offset_y,
+                viewport_rect.size.width,
+                content_height,
+            ),
+            &interaction.path,
+            text_system,
+            perf_stats,
+            layout_cache,
+        );
+        let (scrollbar_track, scrollbar_thumb) = scrollbar_geometry(
+            content,
+            scroll_box.scrollbar,
+            content_height,
+            viewport_rect.size.height,
+            offset_y,
+        );
+        interaction.scroll_metrics = Some(ScrollMetrics {
+            viewport_rect,
+            content_height,
+            offset_y,
+            max_offset_y: (content_height - viewport_rect.size.height).max(0.0),
+            scrollbar_track,
+            scrollbar_thumb,
+        });
+        return interaction;
+    }
+
+    if element.text_node().is_some()
+        || element.image_node().is_some()
+        || element.children.is_empty()
+    {
+        return interaction;
+    }
+
+    let content = inset_rect(rect, content_insets(&element.style));
+    interaction.children = layout_interaction_skeleton_children(
+        element,
+        content,
+        &interaction.path,
+        text_system,
+        perf_stats,
+        layout_cache,
+    );
+    interaction
+}
+
+fn layout_interaction_skeleton_children(
+    element: &Element,
+    content: Rect,
+    path: &LayoutPath,
+    text_system: &mut TextSystem,
+    perf_stats: &mut LayoutPerfStats,
+    layout_cache: &mut LayoutCache,
+) -> Vec<LayoutNode> {
+    if element.children.is_empty() || content.size.width <= 0.0 || content.size.height <= 0.0 {
+        return Vec::new();
+    }
+
+    let gap_count = element.children.len().saturating_sub(1) as f32;
+    let total_gap = element.style.gap * gap_count;
+    let available_main =
+        (main_axis_size(content.size, element.style.direction).max(0.0) - total_gap).max(0.0);
+    let available_cross = cross_axis_size(content.size, element.style.direction).max(0.0);
+
+    let mut measured_children = Vec::with_capacity(element.children.len());
+    let mut fixed_total = 0.0;
+    let mut flex_total = 0.0;
+    for child in &element.children {
+        let child_insets = content_insets(&child.style);
+        let main_inset = main_axis_padding(child_insets, element.style.direction);
+        let cross_inset = cross_axis_padding(child_insets, element.style.direction);
+        let min_cross_outer = child_min_cross_size(child, element.style.direction)
+            .map(|c| (c + cross_inset).max(0.0))
+            .unwrap_or(0.0);
+        let min_main_outer = child_min_main_size(child, element.style.direction)
+            .map(|m| (m + main_inset).max(0.0))
+            .unwrap_or(0.0);
+        let cross = child_cross_size(child, element.style.direction)
+            .map(|c| (c + cross_inset).max(0.0).max(min_cross_outer))
+            .unwrap_or(available_cross.max(min_cross_outer))
+            .min(available_cross.max(min_cross_outer));
+        let explicit_main = child_main_size(child, element.style.direction)
+            .map(|main| (main + main_inset).max(0.0).max(min_main_outer));
+        let is_flex = explicit_main.is_none() && child.style.flex_grow > 0.0;
+        let measured_main = explicit_main.unwrap_or_else(|| {
+            if is_flex {
+                min_main_outer
+            } else {
+                intrinsic_main_size(
+                    child,
+                    element.style.direction,
+                    cross,
+                    available_main,
+                    text_system,
+                    perf_stats,
+                    layout_cache,
+                )
+                .max(min_main_outer)
+            }
+        });
+        let effective_align = child.style.align_self.unwrap_or(element.style.align_items);
+        let natural_cross = if effective_align != AlignItems::Stretch
+            && !is_flex
+            && child_cross_size(child, element.style.direction).is_none()
+        {
+            let offered = match element.style.direction {
+                FlexDirection::Row => UiSize::new(measured_main, available_cross),
+                FlexDirection::Column => UiSize::new(available_cross, measured_main),
+            };
+            let natural = intrinsic_size(child, offered, text_system, perf_stats, layout_cache);
+            Some(
+                cross_axis_size(natural, element.style.direction)
+                    .max(min_cross_outer)
+                    .min(available_cross.max(min_cross_outer)),
+            )
+        } else {
+            None
+        };
+        if is_flex {
+            flex_total += child_flex_weight(child);
+        } else {
+            fixed_total += measured_main;
+        }
+        measured_children.push(MeasuredChild {
+            cross,
+            natural_cross,
+            main: measured_main,
+            is_flex,
+        });
+    }
+
+    let remaining_main = (available_main - fixed_total).max(0.0);
+    let free_space = if flex_total > 0.0 { 0.0 } else { remaining_main };
+    let justify = justify_offsets(
+        element.style.justify_content,
+        free_space,
+        element.children.len(),
+    );
+    let mut cursor = main_axis_origin(content, element.style.direction) + justify.leading;
+    let mut children = Vec::with_capacity(element.children.len());
+    for (index, (child, measured)) in element.children.iter().zip(measured_children).enumerate() {
+        let child_main = if measured.is_flex {
+            let allocated = if flex_total <= 0.0 {
+                0.0
+            } else {
+                remaining_main * (child_flex_weight(child) / flex_total)
+            };
+            let child_insets = content_insets(&child.style);
+            let main_inset = main_axis_padding(child_insets, element.style.direction);
+            let min_main_outer = child_min_main_size(child, element.style.direction)
+                .map(|m| (m + main_inset).max(0.0))
+                .unwrap_or(0.0);
+            allocated.max(min_main_outer)
+        } else {
+            measured.main
+        };
+        let effective_align = child.style.align_self.unwrap_or(element.style.align_items);
+        let actual_cross = measured.natural_cross.unwrap_or(measured.cross);
+        let cross_origin = {
+            let base = cross_axis_origin(content, element.style.direction);
+            match effective_align {
+                AlignItems::Stretch | AlignItems::Start => base,
+                AlignItems::Center => base + (available_cross - actual_cross) * 0.5,
+                AlignItems::End => base + available_cross - actual_cross,
+            }
+        };
+        let child_rect = child_rect(
+            cross_origin,
+            element.style.direction,
+            cursor,
+            child_main.max(0.0),
+            actual_cross,
+        );
+        children.push(layout_interaction_skeleton(
+            child,
+            child_rect,
+            path.child(index),
+            text_system,
+            perf_stats,
+            layout_cache,
+        ));
+        cursor += child_main.max(0.0) + element.style.gap + justify.between;
     }
     children
 }
@@ -1436,6 +1757,7 @@ struct LayoutCacheKey {
     subtree_hash: u64,
     avail_width_bits: u32,
     avail_height_bits: u32,
+    clip_rect_bits: Option<(u32, u32, u32, u32)>,
 }
 
 struct CachedLayout {
@@ -1497,6 +1819,16 @@ fn rects_overlap(a: Rect, b: Rect) -> bool {
         && a.origin.y + a.size.height > b.origin.y
 }
 
+fn cache_clip_rect_bits(rect: Rect, clip_rect: Option<Rect>) -> Option<(u32, u32, u32, u32)> {
+    let clip = clip_rect?;
+    Some((
+        (clip.origin.x - rect.origin.x).round().to_bits(),
+        (clip.origin.y - rect.origin.y).round().to_bits(),
+        clip.size.width.round().to_bits(),
+        clip.size.height.round().to_bits(),
+    ))
+}
+
 fn prepare_image(image: &ImageNode, rect: Rect, element_id: Option<ElementId>) -> PreparedImage {
     let source_size = image.resource.size();
     let source_aspect = if source_size.height > 0.0 {
@@ -1927,13 +2259,197 @@ fn child_rect(
     }
 }
 
+/// Adjustment applied by `justify_content` to the leading offset of the first
+/// child and the extra space inserted between adjacent children (in addition
+/// to `gap`).
+#[derive(Clone, Copy, Debug)]
+struct JustifyOffsets {
+    leading: f32,
+    between: f32,
+}
+
+fn justify_offsets(
+    justify: JustifyContent,
+    free_space: f32,
+    child_count: usize,
+) -> JustifyOffsets {
+    if child_count == 0 {
+        return JustifyOffsets {
+            leading: 0.0,
+            between: 0.0,
+        };
+    }
+    let free = free_space.max(0.0);
+    match justify {
+        JustifyContent::Start => JustifyOffsets {
+            leading: 0.0,
+            between: 0.0,
+        },
+        JustifyContent::End => JustifyOffsets {
+            leading: free,
+            between: 0.0,
+        },
+        JustifyContent::Center => JustifyOffsets {
+            leading: free * 0.5,
+            between: 0.0,
+        },
+        JustifyContent::SpaceBetween => {
+            if child_count < 2 {
+                JustifyOffsets {
+                    leading: 0.0,
+                    between: 0.0,
+                }
+            } else {
+                JustifyOffsets {
+                    leading: 0.0,
+                    between: free / (child_count - 1) as f32,
+                }
+            }
+        }
+        JustifyContent::SpaceAround => {
+            let segment = free / child_count as f32;
+            JustifyOffsets {
+                leading: segment * 0.5,
+                between: segment,
+            }
+        }
+        JustifyContent::SpaceEvenly => {
+            let segment = free / (child_count + 1) as f32;
+            JustifyOffsets {
+                leading: segment,
+                between: segment,
+            }
+        }
+    }
+}
+
 #[cfg(test)]
 mod tests {
-    use super::{LayoutCache, layout_scene, layout_snapshot, layout_snapshot_with_cache};
+    use super::{
+        LayoutCache, LayoutSnapshot, justify_offsets, layout_scene, layout_snapshot,
+        layout_snapshot_with_cache,
+    };
     use crate::scene::{Color, DisplayItem, Point, Quad, Rect, UiSize};
     use crate::text::TextSystem;
     use crate::text::{TextStyle, TextWrap};
-    use crate::tree::{Edges, Element, ElementId, FlexDirection};
+    use crate::tree::{Edges, Element, ElementId, FlexDirection, JustifyContent};
+
+    #[test]
+    fn justify_offsets_match_each_mode() {
+        // 3 children, 60 units of free space.
+        let cases = [
+            (JustifyContent::Start, (0.0, 0.0)),
+            (JustifyContent::End, (60.0, 0.0)),
+            (JustifyContent::Center, (30.0, 0.0)),
+            (JustifyContent::SpaceBetween, (0.0, 30.0)),
+            (JustifyContent::SpaceAround, (10.0, 20.0)),
+            (JustifyContent::SpaceEvenly, (15.0, 15.0)),
+        ];
+        for (mode, (leading, between)) in cases {
+            let off = justify_offsets(mode, 60.0, 3);
+            assert_eq!(
+                (off.leading, off.between),
+                (leading, between),
+                "mode {mode:?}",
+            );
+        }
+    }
+
+    #[test]
+    fn justify_offsets_handle_degenerate_inputs() {
+        // No children: every mode collapses to zero offsets.
+        for mode in [
+            JustifyContent::Start,
+            JustifyContent::End,
+            JustifyContent::Center,
+            JustifyContent::SpaceBetween,
+            JustifyContent::SpaceAround,
+            JustifyContent::SpaceEvenly,
+        ] {
+            let off = justify_offsets(mode, 100.0, 0);
+            assert_eq!((off.leading, off.between), (0.0, 0.0));
+        }
+
+        // Single child: SpaceBetween pins to start, SpaceAround/SpaceEvenly center.
+        let one_between = justify_offsets(JustifyContent::SpaceBetween, 60.0, 1);
+        assert_eq!((one_between.leading, one_between.between), (0.0, 0.0));
+        let one_around = justify_offsets(JustifyContent::SpaceAround, 60.0, 1);
+        assert_eq!(one_around.leading, 30.0);
+        let one_evenly = justify_offsets(JustifyContent::SpaceEvenly, 60.0, 1);
+        assert_eq!(one_evenly.leading, 30.0);
+
+        // Negative free space is clamped to zero.
+        let off = justify_offsets(JustifyContent::Center, -10.0, 3);
+        assert_eq!((off.leading, off.between), (0.0, 0.0));
+    }
+
+    /// End-to-end check that `justify_content` actually shifts child rectangles
+    /// for every mode by laying out three 50-unit boxes in a 300-unit row with
+    /// no padding or gap (so 150 units of free space).
+    #[test]
+    fn justify_content_positions_children_for_each_mode() {
+        fn child_xs(mode: JustifyContent, child_count: usize) -> Vec<f32> {
+            let children: Vec<Element> = (0..child_count)
+                .map(|_| Element::new().width(50.0).background(Color::rgb(1, 0, 0)))
+                .collect();
+            let root = Element::row().justify_content(mode).children(children);
+            let scene = layout_scene(1, UiSize::new(300.0, 100.0), &root);
+            scene
+                .items
+                .iter()
+                .filter_map(|item| match item {
+                    DisplayItem::Quad(q) => Some(q.rect.origin.x),
+                    _ => None,
+                })
+                .collect()
+        }
+
+        // 3 children, free = 300 - 3*50 = 150.
+        assert_eq!(child_xs(JustifyContent::Start, 3), vec![0.0, 50.0, 100.0]);
+        assert_eq!(child_xs(JustifyContent::End, 3), vec![150.0, 200.0, 250.0]);
+        assert_eq!(
+            child_xs(JustifyContent::Center, 3),
+            vec![75.0, 125.0, 175.0],
+        );
+        // SpaceBetween: between = 150/2 = 75.
+        assert_eq!(
+            child_xs(JustifyContent::SpaceBetween, 3),
+            vec![0.0, 125.0, 250.0],
+        );
+        // SpaceAround: segment = 150/3 = 50, leading = 25.
+        assert_eq!(
+            child_xs(JustifyContent::SpaceAround, 3),
+            vec![25.0, 125.0, 225.0],
+        );
+        // SpaceEvenly with 4 children to avoid sub-pixel positions:
+        // free = 300 - 4*50 = 100, segment = 100/5 = 20.
+        assert_eq!(
+            child_xs(JustifyContent::SpaceEvenly, 4),
+            vec![20.0, 90.0, 160.0, 230.0],
+        );
+    }
+
+    #[test]
+    fn justify_content_no_op_when_flex_children_consume_remainder() {
+        // A flex child eats all remaining space, so SpaceBetween should not
+        // shift the fixed sibling away from its normal cursor position.
+        let root = Element::row()
+            .justify_content(JustifyContent::SpaceBetween)
+            .children([
+                Element::new().width(50.0).background(Color::rgb(1, 0, 0)),
+                Element::new().flex(1.0).background(Color::rgb(0, 1, 0)),
+            ]);
+        let scene = layout_scene(1, UiSize::new(300.0, 100.0), &root);
+        let xs: Vec<f32> = scene
+            .items
+            .iter()
+            .filter_map(|item| match item {
+                DisplayItem::Quad(q) => Some(q.rect.origin.x),
+                _ => None,
+            })
+            .collect();
+        assert_eq!(xs, vec![0.0, 50.0]);
+    }
 
     #[test]
     fn row_layout_apportions_fixed_and_flex_children() {
@@ -2625,4 +3141,142 @@ mod tests {
             "expected >= 4 text items visible, got {text_items}"
         );
     }
+
+    #[test]
+    fn cached_scroll_container_recomputes_visible_children_after_offset_changes() {
+        fn scroll_root(offset_y: f32) -> Element {
+            let mut list = Element::column().gap(0.0);
+            for i in 0..20 {
+                list = list.child(
+                    Element::new()
+                        .height(40.0)
+                        .child(Element::text(format!("item {i:02}"), text_style())),
+                );
+            }
+            Element::new().child(
+                Element::scroll_box(offset_y)
+                    .width(400.0)
+                    .height(200.0)
+                    .child(list),
+            )
+        }
+
+        fn visible_texts(snapshot: &LayoutSnapshot) -> Vec<&str> {
+            snapshot
+                .scene
+                .items
+                .iter()
+                .filter_map(|item| match item {
+                    DisplayItem::Text(text) => Some(text.text.as_ref()),
+                    _ => None,
+                })
+                .collect()
+        }
+
+        let mut text_system = TextSystem::new();
+        let mut layout_cache = LayoutCache::new();
+        let size = UiSize::new(400.0, 200.0);
+
+        let first = layout_snapshot_with_cache(
+            1,
+            size,
+            &scroll_root(0.0),
+            &mut text_system,
+            &mut layout_cache,
+        );
+        let second = layout_snapshot_with_cache(
+            2,
+            size,
+            &scroll_root(240.0),
+            &mut text_system,
+            &mut layout_cache,
+        );
+
+        let first_visible = visible_texts(&first);
+        let second_visible = visible_texts(&second);
+        assert!(first_visible.iter().any(|text| text.contains("item 00")));
+        assert!(
+            second_visible.iter().any(|text| text.contains("item 06")),
+            "expected scrolled snapshot to include newly visible rows, got {second_visible:?}"
+        );
+        assert!(
+            !second_visible.iter().any(|text| text.contains("item 00")),
+            "expected initial rows to be culled after scrolling, got {second_visible:?}"
+        );
+    }
+
+    #[test]
+    fn culled_container_keeps_descendant_geometry_for_scroll_into_view() {
+        let target_id = ElementId::new(42);
+        let root = Element::new().child(
+            Element::scroll_box(0.0).width(400.0).height(120.0).child(
+                Element::column()
+                    .child(
+                        Element::column()
+                            .height(160.0)
+                            .child(Element::text("visible group", text_style())),
+                    )
+                    .child(
+                        Element::column().height(160.0).child(
+                            Element::new()
+                                .id(target_id)
+                                .height(40.0)
+                                .child(Element::text("offscreen target", text_style())),
+                        ),
+                    ),
+            ),
+        );
+
+        let snapshot = layout_snapshot(1, UiSize::new(400.0, 120.0), &root);
+
+        assert!(
+            snapshot
+                .scene
+                .items
+                .iter()
+                .all(|item| !matches!(item, DisplayItem::Text(text) if text.text.contains("offscreen target"))),
+            "offscreen target text should still be scene-culled"
+        );
+        assert!(
+            snapshot
+                .interaction_tree
+                .rect_for_element(target_id)
+                .is_some(),
+            "offscreen descendants must keep geometry for widget-ref scrolling"
+        );
+    }
+
+    #[test]
+    fn scroll_culling_keeps_visible_text_selectable_inside_viewport_clip() {
+        let text_id = ElementId::new(77);
+        let root = Element::new().child(
+            Element::scroll_box(120.0).width(360.0).height(120.0).child(
+                Element::paragraph(
+                    "line 01\nline 02\nline 03\nline 04\nline 05\nline 06\nline 07\nline 08\nline 09",
+                    text_style().with_line_height(20.0),
+                )
+                .id(text_id),
+            ),
+        );
+
+        let snapshot = layout_snapshot(1, UiSize::new(360.0, 120.0), &root);
+        let text = snapshot
+            .interaction_tree
+            .text_for_element(text_id)
+            .expect("selectable text should remain in the interaction tree");
+        let visible_hit = snapshot
+            .interaction_tree
+            .text_hit_test(Point::new(8.0, 8.0))
+            .expect("visible scrolled text should be selectable");
+
+        assert_eq!(text.element_id, Some(text_id));
+        assert_eq!(visible_hit.target.element_id, Some(text_id));
+        assert!(
+            snapshot
+                .interaction_tree
+                .text_hit_test(Point::new(8.0, 160.0))
+                .is_none(),
+            "text hit testing should still honor the scroll viewport clip"
+        );
+    }
 }

lib/ui/src/lib.rs

@@ -9,6 +9,7 @@ pub(crate) mod trace_targets {
     #![allow(dead_code)]
     pub const PLATFORM: &str = "ruin_ui::platform";
     pub const SCENE: &str = "ruin_ui::scene";
+    #[allow(dead_code)]
     pub const TEXT_PERF: &str = "ruin_ui::text_perf";
 }
 
@@ -30,14 +31,15 @@ pub use interaction::{
 };
 pub use keyboard::{KeyboardEvent, KeyboardEventKind, KeyboardKey, KeyboardModifiers};
 pub use layout::{
-    HitTarget, InteractionTree, LayoutCache, LayoutNode, LayoutPath, LayoutSnapshot, ScrollMetrics,
+    HitTarget, InteractionTree, LayoutCache, LayoutFrameStats, LayoutNode, LayoutPath,
-    TextHitTarget, element_min_size, layout_snapshot, layout_snapshot_with_cache,
+    LayoutSnapshot, ScrollMetrics, TextHitTarget, element_min_size, layout_snapshot,
+    layout_snapshot_with_cache, layout_snapshot_with_cache_and_stats,
     layout_snapshot_with_text_system,
 };
 pub use layout::{layout_scene, layout_scene_with_text_system};
 pub use platform::{
     PlatformClosed, PlatformEndpoint, PlatformEvent, PlatformProxy, PlatformRequest,
-    PlatformRuntime, start_headless,
+    PlatformRuntime, set_command_wake_hook, start_headless,
 };
 pub use runtime::{EventStreamClosed, UiRuntime, WindowController};
 pub use scene::{
@@ -51,7 +53,7 @@ pub use text::{
 };
 pub use tree::{
     AlignItems, Border, BoxShadow, BoxShadowKind, CornerRadius, CursorIcon, Edges, Element,
-    ElementId, FlexDirection, ScrollbarStyle, Style,
+    ElementId, FlexDirection, JustifyContent, ScrollbarStyle, Style,
 };
 pub use window::{
     DecorationMode, WindowConfigured, WindowId, WindowLifecycle, WindowSpec, WindowUpdate,

lib/ui/src/platform.rs

@@ -4,8 +4,8 @@ use std::cell::RefCell;
 use std::collections::BTreeMap;
 use std::fmt;
 use std::rc::Rc;
-use std::sync::Arc;
 use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::{Arc, Mutex, OnceLock};
 
 use ruin_runtime::channel::mpsc;
 use ruin_runtime::{WorkerHandle, queue_future, queue_microtask, spawn_worker};
@@ -18,6 +18,13 @@ use crate::trace_targets;
 use crate::tree::CursorIcon;
 use crate::window::{WindowConfigured, WindowId, WindowLifecycle, WindowSpec, WindowUpdate};
 
+type CommandWakeHook = Arc<dyn Fn() + Send + Sync + 'static>;
+
+fn command_wake_hook() -> &'static Mutex<Option<CommandWakeHook>> {
+    static HOOK: OnceLock<Mutex<Option<CommandWakeHook>>> = OnceLock::new();
+    HOOK.get_or_init(|| Mutex::new(None))
+}
+
 #[derive(Clone)]
 pub struct PlatformProxy {
     command_tx: mpsc::UnboundedSender<PlatformRequest>,
@@ -32,7 +39,7 @@ pub struct PlatformProxy {
 pub struct PlatformRuntime {
     proxy: PlatformProxy,
     events: mpsc::Receiver<PlatformEvent>,
-    _worker: WorkerHandle,
+    worker: Option<WorkerHandle>,
 }
 
 pub struct PlatformEndpoint {
@@ -73,6 +80,7 @@ pub enum PlatformEvent {
         window_id: WindowId,
         text: String,
     },
+    #[cfg(target_os = "linux")]
     PrimarySelectionText {
         window_id: WindowId,
         text: String,
@@ -118,10 +126,12 @@ pub enum PlatformRequest {
     RequestClipboardText {
         window_id: WindowId,
     },
+    #[cfg(target_os = "linux")]
     SetPrimarySelectionText {
         window_id: WindowId,
         text: String,
     },
+    #[cfg(target_os = "linux")]
     RequestPrimarySelectionText {
         window_id: WindowId,
     },
@@ -203,7 +213,30 @@ impl PlatformRuntime {
         Self {
             proxy,
             events: event_rx,
-            _worker: worker,
+            worker: Some(worker),
+        }
+    }
+
+    /// Creates a platform runtime hosted by the current runtime thread.
+    ///
+    /// This is useful for backends that must run on a specific host thread
+    /// (for example, AppKit on macOS main thread).
+    pub fn custom_local(start: impl FnOnce(PlatformEndpoint)) -> Self {
+        let (command_tx, command_rx) = mpsc::unbounded_channel::<PlatformRequest>();
+        let (event_tx, event_rx) = mpsc::unbounded_channel::<PlatformEvent>();
+        let proxy = PlatformProxy {
+            command_tx,
+            next_window_id: Arc::new(AtomicU64::new(1)),
+        };
+        start(PlatformEndpoint {
+            commands: command_rx,
+            events: event_tx,
+        });
+
+        Self {
+            proxy,
+            events: event_rx,
+            worker: None,
         }
     }
 
@@ -216,6 +249,7 @@ impl PlatformRuntime {
     }
 
     pub fn take_pending_events(&mut self) -> Vec<PlatformEvent> {
+        let _ = self.worker.as_ref();
         let mut events = Vec::new();
         while let Ok(event) = self.events.try_recv() {
             events.push(event);
@@ -247,6 +281,7 @@ impl PlatformProxy {
         self.send(PlatformRequest::ReplaceScene { window_id, scene })
     }
 
+    #[cfg(target_os = "linux")]
     pub fn set_primary_selection_text(
         &self,
         window_id: WindowId,
@@ -258,6 +293,7 @@ impl PlatformProxy {
         })
     }
 
+    #[cfg(target_os = "linux")]
     pub fn request_primary_selection_text(
         &self,
         window_id: WindowId,
@@ -317,7 +353,20 @@ impl PlatformProxy {
     }
 
     fn send(&self, command: PlatformRequest) -> Result<(), PlatformClosed> {
-        self.command_tx.send(command).map_err(|_| PlatformClosed)
+        self.command_tx.send(command).map_err(|_| PlatformClosed)?;
+        if let Ok(hook) = command_wake_hook().lock()
+            && let Some(hook) = hook.as_ref().cloned()
+        {
+            hook();
+        }
+        Ok(())
+    }
+}
+
+#[doc(hidden)]
+pub fn set_command_wake_hook(hook: Option<CommandWakeHook>) {
+    if let Ok(mut slot) = command_wake_hook().lock() {
+        *slot = hook;
     }
 }
 
@@ -356,7 +405,9 @@ pub fn start_headless() -> PlatformRuntime {
                             }
                             PlatformRequest::SetClipboardText { .. } => {}
                             PlatformRequest::RequestClipboardText { .. } => {}
+                            #[cfg(target_os = "linux")]
                             PlatformRequest::SetPrimarySelectionText { .. } => {}
+                            #[cfg(target_os = "linux")]
                             PlatformRequest::RequestPrimarySelectionText { .. } => {}
                             PlatformRequest::SetCursorIcon { .. } => {}
                             PlatformRequest::EmitCloseRequested { window_id } => {

lib/ui/src/runtime.rs

@@ -110,6 +110,7 @@ impl WindowController {
     }
 
     /// Copies plain text to the platform primary-selection buffer for this window.
+    #[cfg(target_os = "linux")]
     pub fn set_primary_selection_text(
         &self,
         text: impl Into<String>,
@@ -128,6 +129,7 @@ impl WindowController {
     }
 
     /// Requests the current plain-text primary selection contents from the platform.
+    #[cfg(target_os = "linux")]
     pub fn request_primary_selection_text(&self) -> Result<(), PlatformClosed> {
         self.proxy.request_primary_selection_text(self.id)
     }

lib/ui/src/scene.rs

@@ -189,7 +189,7 @@ pub struct PreparedTextLine {
 #[derive(Clone, Debug, PartialEq)]
 pub struct PreparedText {
     pub element_id: Option<ElementId>,
-    pub text: String,
+    pub text: Arc<str>,
     pub origin: Point,
     pub bounds: Option<UiSize>,
     pub font_size: f32,
@@ -206,6 +206,8 @@ pub struct PreparedText {
 /// Add `origin` to convert to absolute window coords.
 #[derive(Clone, Debug, PartialEq)]
 pub struct TextLayoutData {
+    pub text: Arc<str>,
+    pub cache_key: u64,
     pub lines: Vec<PreparedTextLine>,
     pub glyphs: Vec<GlyphInstance>,
     /// Measured (unclamped) size of the laid-out text.
@@ -225,7 +227,6 @@ impl PreparedText {
     #[allow(clippy::too_many_arguments)]
     pub(crate) fn from_layout(
         element_id: Option<ElementId>,
-        text: String,
         origin: Point,
         bounds: Option<UiSize>,
         font_size: f32,
@@ -237,7 +238,7 @@ impl PreparedText {
     ) -> Self {
         Self {
             element_id,
-            text,
+            text: layout.text.clone(),
             origin,
             bounds,
             font_size,
@@ -256,6 +257,10 @@ impl PreparedText {
         Arc::as_ptr(&self.layout)
     }
 
+    pub fn layout_cache_key(&self) -> u64 {
+        self.layout.cache_key
+    }
+
     /// Create a monospace `PreparedText` without going through the text system.
     /// Used for testing and low-level terminal-style rendering.
     pub fn monospace(
@@ -265,7 +270,7 @@ impl PreparedText {
         advance: f32,
         color: Color,
     ) -> Self {
-        let text = text.into();
+        let text: Arc<str> = Arc::from(text.into());
         // Glyphs are stored in LOCAL (origin-relative) coordinates.
         let mut local_x = 0.0f32;
         let mut glyphs = Vec::with_capacity(text.chars().count());
@@ -293,7 +298,7 @@ impl PreparedText {
         let size = UiSize::new(local_x, font_size);
         Self {
             element_id: None,
-            text,
+            text: text.clone(),
             origin,
             bounds: None,
             font_size,
@@ -302,6 +307,8 @@ impl PreparedText {
             selectable: true,
             selection_style: TextSelectionStyle::DEFAULT,
             layout: Arc::new(TextLayoutData {
+                text: text.clone(),
+                cache_key: monospace_text_cache_key(&text, font_size, advance, color),
                 lines: vec![line],
                 glyphs,
                 size,
@@ -466,7 +473,10 @@ impl PreparedText {
         if range.is_empty() {
             return;
         }
-        for glyph in Arc::make_mut(&mut self.layout).glyphs.iter_mut() {
+        let layout = Arc::make_mut(&mut self.layout);
+        layout.cache_key =
+            selected_text_cache_key(layout.cache_key, range.start, range.end, selected_color);
+        for glyph in layout.glyphs.iter_mut() {
             if glyph.text_end > range.start && glyph.text_start < range.end {
                 glyph.color = selected_color;
             }
@@ -583,6 +593,28 @@ impl PreparedText {
     }
 }
 
+fn monospace_text_cache_key(text: &str, font_size: f32, advance: f32, color: Color) -> u64 {
+    use std::hash::{DefaultHasher, Hash, Hasher};
+
+    let mut hasher = DefaultHasher::new();
+    text.hash(&mut hasher);
+    font_size.to_bits().hash(&mut hasher);
+    advance.to_bits().hash(&mut hasher);
+    color.hash(&mut hasher);
+    hasher.finish()
+}
+
+fn selected_text_cache_key(base: u64, start: usize, end: usize, color: Color) -> u64 {
+    use std::hash::{DefaultHasher, Hash, Hasher};
+
+    let mut hasher = DefaultHasher::new();
+    base.hash(&mut hasher);
+    start.hash(&mut hasher);
+    end.hash(&mut hasher);
+    color.hash(&mut hasher);
+    hasher.finish()
+}
+
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 enum WordClass {
     Word,
@@ -886,6 +918,8 @@ mod tests {
         }
         let orig_size = text.layout.size;
         text.layout = Arc::new(TextLayoutData {
+            text: text.text.clone(),
+            cache_key: text.layout.cache_key,
             lines,
             glyphs,
             size: orig_size,

lib/ui/src/text.rs

@@ -10,8 +10,9 @@ use cosmic_text::{
 };
 use fontconfig::Fontconfig;
 
-use crate::{Color, GlyphInstance, Point, PreparedText, PreparedTextLine, Rect, TextLayoutData,
+use crate::{
-            UiSize};
+    Color, GlyphInstance, Point, PreparedText, PreparedTextLine, Rect, TextLayoutData, UiSize,
+};
 
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 pub enum TextAlign {
@@ -268,7 +269,7 @@ pub struct TextSystem {
 }
 
 #[derive(Clone, Copy, Debug, Default)]
-pub(crate) struct TextFrameStats {
+pub struct TextFrameStats {
     pub requests: u32,
     pub cache_hits: u32,
     pub cache_misses: u32,
@@ -340,7 +341,6 @@ impl TextSystem {
         bounds: Option<UiSize>,
     ) -> PreparedText {
         let bounds = bounds.or(style.bounds);
-        let text = combined_text(spans);
         // Use the cached Arc directly — glyphs are in local (origin-0) coords.
         let layout_data = self.layout(
             spans,
@@ -351,7 +351,6 @@ impl TextSystem {
 
         PreparedText::from_layout(
             None,
-            text,
             origin,
             bounds,
             style.font_size,
@@ -443,7 +442,11 @@ impl TextSystem {
             // For no-wrap + start-aligned text, width doesn't affect shaping.
             // Pass None so cosmic-text doesn't truncate and the result is
             // consistent with the width-independent cache key.
-            let effective_width = if width_affects_layout(style) { width } else { None };
+            let effective_width = if width_affects_layout(style) {
+                width
+            } else {
+                None
+            };
             borrowed.set_size(effective_width, None);
             let default_attrs = default_attrs_for_style(style, default_family.as_deref());
             if uses_plain_text_fast_path {
@@ -471,7 +474,8 @@ impl TextSystem {
         }
         self.frame_stats.buffer_build_ms += buffer_build_started.elapsed().as_secs_f64() * 1_000.0;
 
-        let line_starts = line_start_offsets(&combined_text(spans));
+        let text = combined_text(spans);
+        let line_starts = line_start_offsets(&text);
         let mut measured_width: f32 = 0.0;
         let mut measured_height: f32 = 0.0;
         let mut lines = Vec::new();
@@ -495,9 +499,7 @@ impl TextSystem {
                     // is color-independent.  Per-span colors (from glyph.color_opt)
                     // are stored directly since they are part of the shape key via
                     // the spans hash.
-                    color: glyph
+                    color: glyph.color_opt.map_or(Color::SENTINEL, color_from_cosmic),
-                        .color_opt
-                        .map_or(Color::SENTINEL, color_from_cosmic),
                     cache_key: Some(physical.cache_key),
                     text_start: line_offset + glyph.start,
                     text_end: line_offset + glyph.end,
@@ -524,6 +526,8 @@ impl TextSystem {
             glyph_collect_started.elapsed().as_secs_f64() * 1_000.0;
 
         let layout = Arc::new(TextLayoutData {
+            text: Arc::from(text),
+            cache_key,
             lines,
             glyphs,
             size: UiSize::new(measured_width.max(0.0), measured_height.max(0.0)),
@@ -696,16 +700,16 @@ fn attrs_for_span<'a>(
         base
     };
     base.weight(match span.weight {
-            TextSpanWeight::Normal => CosmicWeight::NORMAL,
+        TextSpanWeight::Normal => CosmicWeight::NORMAL,
-            TextSpanWeight::Medium => CosmicWeight::MEDIUM,
+        TextSpanWeight::Medium => CosmicWeight::MEDIUM,
-            TextSpanWeight::Semibold => CosmicWeight::SEMIBOLD,
+        TextSpanWeight::Semibold => CosmicWeight::SEMIBOLD,
-            TextSpanWeight::Bold => CosmicWeight::BOLD,
+        TextSpanWeight::Bold => CosmicWeight::BOLD,
-        })
+    })
-        .style(match span.slant {
+    .style(match span.slant {
-            TextSpanSlant::Normal => CosmicStyle::Normal,
+        TextSpanSlant::Normal => CosmicStyle::Normal,
-            TextSpanSlant::Italic => CosmicStyle::Italic,
+        TextSpanSlant::Italic => CosmicStyle::Italic,
-            TextSpanSlant::Oblique => CosmicStyle::Oblique,
+        TextSpanSlant::Oblique => CosmicStyle::Oblique,
-        })
+    })
 }
 
 fn to_cosmic_color(color: Color) -> CosmicColor {
@@ -930,7 +934,9 @@ impl std::hash::Hash for TextStyle {
         self.line_height.to_bits().hash(state);
         self.color.hash(state);
         self.font_family.hash(state);
-        self.bounds.map(|b| (b.width.to_bits(), b.height.to_bits())).hash(state);
+        self.bounds
+            .map(|b| (b.width.to_bits(), b.height.to_bits()))
+            .hash(state);
         self.wrap.hash(state);
         self.align.hash(state);
         self.max_lines.hash(state);
@@ -1038,16 +1044,32 @@ mod tests {
         let blue = text_system.prepare("hello", origin, &style_blue);
         // Both PreparedTexts must have identical glyph shapes and sentinel colors —
         // the second call hits the shape cache and produces the same layout data.
-        assert_eq!(red.glyphs.len(), blue.glyphs.len(), "glyph count must match");
+        assert_eq!(
+            red.glyphs.len(),
+            blue.glyphs.len(),
+            "glyph count must match"
+        );
         for (r, b) in red.glyphs.iter().zip(blue.glyphs.iter()) {
             assert_eq!(r.position, b.position, "glyph positions must match");
             assert_eq!(r.cache_key, b.cache_key, "glyph cache keys must match");
-            assert_eq!(r.color, Color::SENTINEL, "default-color glyphs must use SENTINEL");
+            assert_eq!(
-            assert_eq!(b.color, Color::SENTINEL, "default-color glyphs must use SENTINEL");
+                r.color,
+                Color::SENTINEL,
+                "default-color glyphs must use SENTINEL"
+            );
+            assert_eq!(
+                b.color,
+                Color::SENTINEL,
+                "default-color glyphs must use SENTINEL"
+            );
         }
         // PreparedText::clone() is an Arc clone — O(1).
         let cloned = red.clone();
-        assert_eq!(cloned.layout_ptr(), red.layout_ptr(), "clone must share the same Arc");
+        assert_eq!(
+            cloned.layout_ptr(),
+            red.layout_ptr(),
+            "clone must share the same Arc"
+        );
         // But they should carry different default colors.
         assert_eq!(red.default_color, Color::rgb(0xFF, 0x00, 0x00));
         assert_eq!(blue.default_color, Color::rgb(0x00, 0x00, 0xFF));

lib/ui/src/tree.rs

@@ -32,6 +32,36 @@ pub enum AlignItems {
     End,
 }
 
+/// Controls how children are positioned and how leftover space is distributed
+/// along the main axis (horizontal for `FlexDirection::Row`, vertical for
+/// `FlexDirection::Column`).
+///
+/// When a container has flex children (`flex_grow > 0`) all remaining space is
+/// consumed by them, so `justify_content` has no visible effect on the main
+/// axis distribution in that case. The container's `gap` is always honored as
+/// a minimum between adjacent children — `SpaceBetween`, `SpaceAround`, and
+/// `SpaceEvenly` distribute leftover space *in addition to* `gap`.
+#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
+pub enum JustifyContent {
+    /// Pack children at the start of the main axis. This is the default and
+    /// matches the behavior before `justify_content` existed.
+    #[default]
+    Start,
+    /// Pack children at the end of the main axis.
+    End,
+    /// Pack children as a group, centered along the main axis.
+    Center,
+    /// Distribute children with the first child flush with the start, the last
+    /// child flush with the end, and equal extra space between adjacent pairs.
+    SpaceBetween,
+    /// Distribute children with equal extra space around each child, so the
+    /// space at the ends is half of the space between adjacent children.
+    SpaceAround,
+    /// Distribute children so the space between adjacent children and between
+    /// the children and both edges of the container is identical.
+    SpaceEvenly,
+}
+
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 pub enum CursorIcon {
     Default,
@@ -192,6 +222,7 @@ pub struct Style {
     pub align_items: AlignItems,
     /// Per-element override of the parent container's `align_items`. `None` means inherit.
     pub align_self: Option<AlignItems>,
+    pub justify_content: JustifyContent,
     pub width: Option<f32>,
     pub height: Option<f32>,
     pub min_width: Option<f32>,
@@ -214,6 +245,7 @@ impl Default for Style {
             direction: FlexDirection::Column,
             align_items: AlignItems::Stretch,
             align_self: None,
+            justify_content: JustifyContent::Start,
             width: None,
             height: None,
             min_width: None,
@@ -244,6 +276,7 @@ enum ElementContent {
 pub(crate) struct TextNode {
     pub spans: Vec<TextSpan>,
     pub style: TextStyle,
+    content_hash: u64,
 }
 
 #[derive(Clone, Debug, PartialEq)]
@@ -281,12 +314,14 @@ impl Element {
     }
 
     pub fn spans(spans: impl IntoIterator<Item = TextSpan>, style: TextStyle) -> Self {
+        let spans = spans.into_iter().collect::<Vec<_>>();
         Self {
             id: None,
             style: Style::default(),
             children: Vec::new(),
             content: ElementContent::Text(TextNode {
-                spans: spans.into_iter().collect(),
+                content_hash: text_node_content_hash(&spans, &style),
+                spans,
                 style,
             }),
         }
@@ -424,6 +459,11 @@ impl Element {
         self
     }
 
+    pub fn justify_content(mut self, justify: JustifyContent) -> Self {
+        self.style.justify_content = justify;
+        self
+    }
+
     pub fn cursor(mut self, cursor: CursorIcon) -> Self {
         self.style.cursor = Some(cursor);
         self
@@ -575,11 +615,18 @@ impl Hash for AlignItems {
     }
 }
 
+impl Hash for JustifyContent {
+    fn hash<H: Hasher>(&self, state: &mut H) {
+        (*self as u8).hash(state);
+    }
+}
+
 impl Hash for Style {
     fn hash<H: Hasher>(&self, state: &mut H) {
         self.direction.hash(state);
         self.align_items.hash(state);
         self.align_self.hash(state);
+        self.justify_content.hash(state);
         self.width.map(f32::to_bits).hash(state);
         self.height.map(f32::to_bits).hash(state);
         self.min_width.map(f32::to_bits).hash(state);
@@ -599,8 +646,7 @@ impl Hash for Style {
 
 impl Hash for TextNode {
     fn hash<H: Hasher>(&self, state: &mut H) {
-        self.spans.hash(state);
+        self.content_hash.hash(state);
-        self.style.hash(state);
     }
 }
 
@@ -611,6 +657,15 @@ impl Hash for ImageNode {
     }
 }
 
+fn text_node_content_hash(spans: &[TextSpan], style: &TextStyle) -> u64 {
+    use std::hash::DefaultHasher;
+
+    let mut hasher = DefaultHasher::new();
+    spans.hash(&mut hasher);
+    style.hash(&mut hasher);
+    hasher.finish()
+}
+
 impl Hash for ScrollBoxNode {
     fn hash<H: Hasher>(&self, state: &mut H) {
         self.offset_y.to_bits().hash(state);

lib/ui/src/window.rs

@@ -34,6 +34,11 @@ pub enum WindowLifecycle {
 
 #[derive(Clone, Copy, Debug, PartialEq)]
 pub struct WindowConfigured {
+    /// Current logical content size and platform presentation scale.
+    ///
+    /// Backends should emit a new configuration when either the logical size or
+    /// scale changes. This lets hosts relayout for size changes while renderers
+    /// can update drawable/text scale when a window moves between displays.
     pub actual_inner_size: UiSize,
     pub scale_factor: f32,
     pub visible: bool,

lib/ui_platform_macos/Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "ruin_ui_platform_macos"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+ruin_ui = { path = "../ui" }
+ruin_ui_renderer_wgpu = { path = "../ui_renderer_wgpu" }
+ruin_runtime = { package = "ruin-runtime", path = "../runtime" }
+tracing = "0.1"
+
+[target.'cfg(target_os = "macos")'.dependencies]
+libc = "0.2"
+objc2 = "0.6.4"
+objc2-core-foundation = "0.3.2"
+objc2-foundation = "0.3.2"
+objc2-quartz-core = "0.3.2"
+raw-window-handle = "0.6"
+raw-window-metal = "1.1.0"

lib/ui_platform_wayland/Cargo.toml

@@ -4,12 +4,14 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
-libc = "0.2"
-raw-window-handle = "0.6"
 ruin_runtime = { package = "ruin-runtime", path = "../runtime" }
 ruin_ui = { path = "../ui" }
 ruin_ui_renderer_wgpu = { path = "../ui_renderer_wgpu" }
 tracing = "0.1"
+
+[target.'cfg(target_os = "linux")'.dependencies]
+libc = "0.2"
+raw-window-handle = "0.6"
 wayland-backend = { version = "0.3", features = ["client_system"] }
 wayland-client = "0.31"
 wayland-protocols = { version = "0.32", features = ["client", "staging", "unstable"] }

lib/ui_platform_wayland/src/lib.rs

@@ -1,3 +1,5 @@
+#![cfg(target_os = "linux")]
+
 use std::cell::RefCell;
 use std::collections::BTreeMap;
 use std::error::Error;
@@ -40,13 +42,13 @@ use wayland_client::{
 use wayland_protocols::wp::cursor_shape::v1::client::{
     wp_cursor_shape_device_v1, wp_cursor_shape_manager_v1,
 };
-use wayland_protocols::xdg::decoration::zv1::client::{
-    zxdg_decoration_manager_v1, zxdg_toplevel_decoration_v1,
-};
 use wayland_protocols::wp::primary_selection::zv1::client::{
     zwp_primary_selection_device_manager_v1, zwp_primary_selection_device_v1,
     zwp_primary_selection_offer_v1, zwp_primary_selection_source_v1,
 };
+use wayland_protocols::xdg::decoration::zv1::client::{
+    zxdg_decoration_manager_v1, zxdg_toplevel_decoration_v1,
+};
 use wayland_protocols::xdg::shell::client::{xdg_surface, xdg_toplevel, xdg_wm_base};
 use xkbcommon::xkb;
 
@@ -242,7 +244,10 @@ fn fixed_size_request_for_spec(spec: &WindowSpec) -> Option<(u32, u32)> {
         .or(spec.min_inner_size)
         .or(spec.max_inner_size)
         .unwrap_or_else(|| UiSize::new(800.0, 500.0));
-    Some((size.width.max(1.0).round() as u32, size.height.max(1.0).round() as u32))
+    Some((
+        size.width.max(1.0).round() as u32,
+        size.height.max(1.0).round() as u32,
+    ))
 }
 
 fn wayland_cursor_shape(icon: CursorIcon) -> wp_cursor_shape_device_v1::Shape {
@@ -1352,7 +1357,9 @@ fn spawn_window_worker(
                                             "worker observed resized frame"
                                         );
                                         state_ref.pending_viewport = Some(current_viewport);
-                                        state_ref.pending_viewport_since.get_or_insert_with(Instant::now);
+                                        state_ref
+                                            .pending_viewport_since
+                                            .get_or_insert_with(Instant::now);
                                         // Emit configure BEFORE touching the GPU so the app
                                         // thread starts layout immediately in parallel.
                                         // The actual swapchain recreation is deferred to just
@@ -1397,7 +1404,9 @@ fn spawn_window_worker(
                                                 "scene size does not match current viewport; holding last buffer"
                                             );
                                             state_ref.pending_viewport = Some(current_viewport);
-                                            state_ref.pending_viewport_since.get_or_insert_with(Instant::now);
+                                            state_ref
+                                                .pending_viewport_since
+                                                .get_or_insert_with(Instant::now);
                                             // Deadlock prevention: if the app responded to the
                                             // configure we sent (scene matches in_flight) but the
                                             // viewport has since moved on, clear the in_flight
@@ -1421,7 +1430,9 @@ fn spawn_window_worker(
                                             // before rendering.  Deferring from frame.resized means
                                             // rapid configures pay one recreation instead of one
                                             // per event.
-                                            if let Some((w, h)) = state_ref.pending_swapchain_size.take() {
+                                            if let Some((w, h)) =
+                                                state_ref.pending_swapchain_size.take()
+                                            {
                                                 let t_resize = std::time::Instant::now();
                                                 state_ref.renderer.resize(w, h);
                                                 let resize_gpu_us = t_resize.elapsed().as_micros();
@@ -1438,7 +1449,8 @@ fn spawn_window_worker(
                                             let t_render = std::time::Instant::now();
                                             match state_ref.renderer.render(scene) {
                                                 Ok(()) => {
-                                                    let render_gpu_us = t_render.elapsed().as_micros();
+                                                    let render_gpu_us =
+                                                        t_render.elapsed().as_micros();
                                                     debug!(
                                                         target: "ruin_ui_platform_wayland::perf",
                                                         window_id = state_ref.window_id.raw(),
@@ -1520,10 +1532,10 @@ fn spawn_window_worker(
                                 {
                                     let delay =
                                         repeat.next_at.saturating_duration_since(Instant::now());
-                                    state_ref.keyboard_repeat_timer = Some(set_timeout(
+                                    state_ref.keyboard_repeat_timer =
-                                        delay,
+                                        Some(set_timeout(delay, move || {
-                                        move || write_wakeup(pipe_write_fd),
+                                            write_wakeup(pipe_write_fd)
-                                    ));
+                                        }));
                                 }
                             }
                         }

lib/ui_renderer_wgpu/src/lib.rs

@@ -91,7 +91,8 @@ struct PreparedGlyphBitmap {
 
 struct RasterizedText {
     origin_offset: Point,
-    size: UiSize,
+    draw_size: UiSize,
+    texture_size: UiSize,
     pixels: Vec<u8>,
 }
 
@@ -168,21 +169,12 @@ struct UploadedAtlasText {
 
 #[derive(Clone, Debug, Eq, Hash, PartialEq)]
 struct TextTextureKey {
-    text: String,
+    layout_key: u64,
-    bounds: Option<(u32, u32)>,
+    bounds: Option<(i32, i32)>,
+    clip: Option<(i32, i32, i32, i32)>,
     font_size_bits: u32,
     line_height_bits: u32,
     color: (u8, u8, u8, u8),
-    glyphs: Vec<TextTextureGlyph>,
-}
-
-#[derive(Clone, Debug, Eq, Hash, PartialEq)]
-struct TextTextureGlyph {
-    local_x_bits: u32,
-    local_y_bits: u32,
-    advance_bits: u32,
-    color: (u8, u8, u8, u8),
-    cache_key: Option<CacheKey>,
 }
 
 const VERTEX_ATTRIBUTES: [wgpu::VertexAttribute; 11] = [
@@ -313,6 +305,21 @@ pub enum RenderError {
     Validation,
 }
 
+#[derive(Clone, Copy, Debug, Default, PartialEq)]
+pub struct RendererFrameStats {
+    pub scene_version: u64,
+    pub scene_items: usize,
+    pub quad_vertices: usize,
+    pub image_batches: usize,
+    pub atlas_text_vertices: u32,
+    pub fallback_text_batches: usize,
+    pub fallback_text_vertices: u32,
+    pub atlas_glyphs_total: u32,
+    pub atlas_glyphs_clip_culled: u32,
+    pub text_prepare_ms: f64,
+    pub render_ms: f64,
+}
+
 pub struct WgpuSceneRenderer {
     surface: wgpu::Surface<'static>,
     device: wgpu::Device,
@@ -330,7 +337,9 @@ pub struct WgpuSceneRenderer {
     image_cache_order: VecDeque<u64>,
     #[allow(dead_code)]
     glyph_atlas: GlyphAtlas,
+    scale_factor: f32,
     base_color: Color,
+    last_frame_stats: RendererFrameStats,
 }
 
 const MAX_TEXT_CACHE_ENTRIES: usize = 64;
@@ -377,8 +386,11 @@ impl WgpuSceneRenderer {
             format,
             width: width.max(1),
             height: height.max(1),
-            present_mode: wgpu::PresentMode::AutoVsync,
+            // RUIN prioritizes immediate resize/input feedback over frame pacing
-            desired_maximum_frame_latency: 2,
+            // here. Keep latency to one frame and let callers opt into a more
+            // power-conservative policy once presentation settings are exposed.
+            present_mode: wgpu::PresentMode::AutoNoVsync,
+            desired_maximum_frame_latency: 1,
             alpha_mode,
             view_formats: vec![],
         };
@@ -721,7 +733,9 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
             image_cache: HashMap::new(),
             image_cache_order: VecDeque::new(),
             glyph_atlas,
+            scale_factor: 1.0,
             base_color,
+            last_frame_stats: RendererFrameStats::default(),
         })
     }
 
@@ -735,9 +749,37 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
         self.surface.configure(&self.device, &self.config);
     }
 
+    pub fn set_scale_factor(&mut self, scale_factor: f32) {
+        let next = scale_factor.max(1.0);
+        if (self.scale_factor - next).abs() <= f32::EPSILON {
+            return;
+        }
+        self.scale_factor = next;
+        // Text cache is scale-dependent; flush on scale transitions (e.g. display move).
+        self.text_cache.clear();
+        self.text_cache_order.clear();
+        self.glyph_atlas = create_glyph_atlas(
+            &self.device,
+            &self.text_bind_group_layout,
+            &self.text_sampler,
+        );
+    }
+
+    pub fn last_frame_stats(&self) -> RendererFrameStats {
+        self.last_frame_stats
+    }
+
     pub fn render(&mut self, scene: &SceneSnapshot) -> Result<(), RenderError> {
+        self.render_with_logical_size(scene, scene.logical_size)
+    }
+
+    pub fn render_with_logical_size(
+        &mut self,
+        scene: &SceneSnapshot,
+        logical_size: UiSize,
+    ) -> Result<(), RenderError> {
         let render_start = std::time::Instant::now();
-        let vertices = build_vertices(scene);
+        let vertices = build_vertices(scene, logical_size);
         let frame = match self.surface.get_current_texture() {
             wgpu::CurrentSurfaceTexture::Success(frame)
             | wgpu::CurrentSurfaceTexture::Suboptimal(frame) => frame,
@@ -761,7 +803,8 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
         let mut uploaded_images = Vec::new();
         let mut uploaded_texts = Vec::new();
         let mut atlas_perf = AtlasTextPerfStats::default();
-        let uploaded_atlas_text = self.prepare_uploaded_atlas_text(scene, &mut atlas_perf);
+        let uploaded_atlas_text =
+            self.prepare_uploaded_atlas_text(scene, logical_size, &mut atlas_perf);
         let mut clip_stack = Vec::new();
         let mut active_clip = ActiveClip::default();
         for item in &scene.items {
@@ -772,7 +815,7 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
                 DisplayItem::PopClip => pop_clip_state(&mut clip_stack, &mut active_clip),
                 DisplayItem::Image(image) => {
                     if let Some(uploaded) =
-                        self.prepare_uploaded_image(image, scene.logical_size, active_clip)
+                        self.prepare_uploaded_image(image, logical_size, active_clip)
                     {
                         uploaded_images.push(uploaded);
                     }
@@ -782,7 +825,7 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
                         continue;
                     }
                     if let Some(uploaded) =
-                        self.prepare_uploaded_text(text, scene.logical_size, active_clip)
+                        self.prepare_uploaded_text(text, logical_size, active_clip)
                     {
                         uploaded_texts.push(uploaded);
                     }
@@ -853,39 +896,60 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
         }
         self.queue.submit([encoder.finish()]);
         frame.present();
-        trace!(
+        self.last_frame_stats = RendererFrameStats {
-            target: "ruin_ui_renderer_wgpu::perf",
+            scene_version: scene.version,
-            scene_version = scene.version,
+            scene_items: scene.items.len(),
-            quad_vertices = vertices.len(),
+            quad_vertices: vertices.len(),
-            image_batches = uploaded_images.len(),
+            image_batches: uploaded_images.len(),
-            atlas_text_vertices = uploaded_atlas_text
+            atlas_text_vertices: uploaded_atlas_text
                 .as_ref()
                 .map_or(0_u32, |text| text.vertex_count),
-            fallback_text_batches = uploaded_texts.len(),
+            fallback_text_batches: uploaded_texts.len(),
-            atlas_glyphs_total = atlas_perf.glyphs_total,
+            fallback_text_vertices: uploaded_texts.iter().map(|text| text.vertex_count).sum(),
-            atlas_glyphs_clip_culled = atlas_perf.glyphs_clip_culled,
+            atlas_glyphs_total: atlas_perf.glyphs_total,
-            text_prepare_ms = text_prepare_ms,
+            atlas_glyphs_clip_culled: atlas_perf.glyphs_clip_culled,
-            render_ms = render_start.elapsed().as_secs_f64() * 1_000.0,
+            text_prepare_ms,
+            render_ms: render_start.elapsed().as_secs_f64() * 1_000.0,
+        };
+        trace!(
+            target: "ruin_ui_renderer_wgpu::perf",
+            scene_version = self.last_frame_stats.scene_version,
+            scene_items = self.last_frame_stats.scene_items,
+            quad_vertices = self.last_frame_stats.quad_vertices,
+            image_batches = self.last_frame_stats.image_batches,
+            atlas_text_vertices = self.last_frame_stats.atlas_text_vertices,
+            fallback_text_batches = self.last_frame_stats.fallback_text_batches,
+            fallback_text_vertices = self.last_frame_stats.fallback_text_vertices,
+            atlas_glyphs_total = self.last_frame_stats.atlas_glyphs_total,
+            atlas_glyphs_clip_culled = self.last_frame_stats.atlas_glyphs_clip_culled,
+            text_prepare_ms = self.last_frame_stats.text_prepare_ms,
+            render_ms = self.last_frame_stats.render_ms,
             "rendered scene"
         );
         Ok(())
     }
 
-    fn rasterize_text(&mut self, text: &PreparedText) -> Option<RasterizedText> {
+    fn rasterize_text(
+        &mut self,
+        text: &PreparedText,
+        raster_clip: Option<Rect>,
+    ) -> Option<RasterizedText> {
         if text.glyphs.iter().all(|glyph| glyph.cache_key.is_some()) {
-            return self.rasterize_prepared_text(text);
+            return self.rasterize_prepared_text(text, raster_clip, self.scale_factor);
         }
 
-        let glyphs = self.collect_glyph_bitmaps(text);
+        let clip = raster_clip.map(|clip| scale_rect_to_pixel_rect(clip, self.scale_factor));
-        let clip = match text.bounds {
+        let glyphs = self.collect_glyph_bitmaps(text, clip);
-            Some(bounds) => PixelRect {
+        let clip = clip
-                left: 0,
+            .or_else(|| {
-                top: 0,
+                text.bounds.map(|bounds| PixelRect {
-                right: bounds.width.ceil() as i32,
+                    left: 0,
-                bottom: bounds.height.ceil() as i32,
+                    top: 0,
-            },
+                    right: (bounds.width * self.scale_factor).ceil() as i32,
-            None => glyph_union(&glyphs)?,
+                    bottom: (bounds.height * self.scale_factor).ceil() as i32,
-        };
+                })
+            })
+            .or_else(|| glyph_union(&glyphs))?;
         if clip.width() == 0 || clip.height() == 0 {
             return None;
         }
@@ -896,23 +960,38 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
         }
 
         Some(RasterizedText {
-            origin_offset: Point::new(clip.left as f32, clip.top as f32),
+            origin_offset: Point::new(
-            size: UiSize::new(clip.width() as f32, clip.height() as f32),
+                clip.left as f32 / self.scale_factor,
+                clip.top as f32 / self.scale_factor,
+            ),
+            draw_size: UiSize::new(
+                clip.width() as f32 / self.scale_factor,
+                clip.height() as f32 / self.scale_factor,
+            ),
+            texture_size: UiSize::new(clip.width() as f32, clip.height() as f32),
             pixels,
         })
     }
 
-    fn rasterize_prepared_text(&mut self, text: &PreparedText) -> Option<RasterizedText> {
+    fn rasterize_prepared_text(
-        let glyphs = self.collect_prepared_glyphs(text);
+        &mut self,
-        let clip = match text.bounds {
+        text: &PreparedText,
-            Some(bounds) => PixelRect {
+        raster_clip: Option<Rect>,
-                left: 0,
+        scale_factor: f32,
-                top: 0,
+    ) -> Option<RasterizedText> {
-                right: bounds.width.ceil() as i32,
+        let clip = raster_clip.map(|clip| scale_rect_to_pixel_rect(clip, scale_factor));
-                bottom: bounds.height.ceil() as i32,
+        let glyphs = self.collect_prepared_glyphs(text, raster_clip, clip, scale_factor);
-            },
+        let clip = raster_clip
-            None => glyph_union_prepared(&glyphs)?,
+            .map(|clip| scale_rect_to_pixel_rect(clip, scale_factor))
-        };
+            .or_else(|| {
+                text.bounds.map(|bounds| PixelRect {
+                    left: 0,
+                    top: 0,
+                    right: (bounds.width * scale_factor).ceil() as i32,
+                    bottom: (bounds.height * scale_factor).ceil() as i32,
+                })
+            })
+            .or_else(|| glyph_union_prepared(&glyphs))?;
         if clip.width() == 0 || clip.height() == 0 {
             return None;
         }
@@ -930,16 +1009,41 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
         }
 
         Some(RasterizedText {
-            origin_offset: Point::new(clip.left as f32, clip.top as f32),
+            origin_offset: Point::new(
-            size: UiSize::new(clip.width() as f32, clip.height() as f32),
+                clip.left as f32 / scale_factor,
+                clip.top as f32 / scale_factor,
+            ),
+            draw_size: UiSize::new(
+                clip.width() as f32 / scale_factor,
+                clip.height() as f32 / scale_factor,
+            ),
+            texture_size: UiSize::new(clip.width() as f32, clip.height() as f32),
             pixels,
         })
     }
 
-    fn collect_prepared_glyphs(&mut self, text: &PreparedText) -> Vec<PreparedGlyphBitmap> {
+    fn collect_prepared_glyphs(
-        let mut glyphs = Vec::with_capacity(text.glyphs.len());
+        &mut self,
-        for glyph in &text.glyphs {
+        text: &PreparedText,
-            let Some(cache_key) = glyph.cache_key else {
+        logical_clip: Option<Rect>,
+        pixel_clip: Option<PixelRect>,
+        scale_factor: f32,
+    ) -> Vec<PreparedGlyphBitmap> {
+        let absolute_clip = logical_clip.map(|clip| {
+            Rect::new(
+                text.origin.x + clip.origin.x,
+                text.origin.y + clip.origin.y,
+                clip.size.width,
+                clip.size.height,
+            )
+        });
+        let visible_glyphs = clip_visible_glyphs(text, absolute_clip);
+        let mut glyphs = Vec::with_capacity(visible_glyphs.len());
+        for glyph in visible_glyphs {
+            let Some(cache_key) = glyph
+                .cache_key
+                .map(|cache_key| scale_glyph_cache_key(cache_key, scale_factor))
+            else {
                 continue;
             };
             let Some(image) = self
@@ -956,15 +1060,19 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
             }
 
             // Glyph positions are LOCAL (origin-relative); no subtraction needed.
-            let local_x = glyph.position.x.round() as i32;
+            let local_x = (glyph.position.x * scale_factor).round() as i32;
-            let local_y = glyph.position.y.round() as i32;
+            let local_y = (glyph.position.y * scale_factor).round() as i32;
+            let rect = PixelRect {
+                left: local_x + image.placement.left,
+                top: local_y - image.placement.top,
+                right: local_x + image.placement.left + width,
+                bottom: local_y - image.placement.top + height,
+            };
+            if pixel_clip.is_some_and(|clip| !pixel_rects_intersect(rect, clip)) {
+                continue;
+            }
             glyphs.push(PreparedGlyphBitmap {
-                rect: PixelRect {
+                rect,
-                    left: local_x + image.placement.left,
-                    top: local_y - image.placement.top,
-                    right: local_x + image.placement.left + width,
-                    bottom: local_y - image.placement.top + height,
-                },
                 cache_key,
                 color: resolve_glyph_color(glyph.color, text.default_color),
             });
@@ -972,19 +1080,33 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
         glyphs
     }
 
-    fn collect_glyph_bitmaps(&mut self, text: &PreparedText) -> Vec<GlyphBitmap> {
+    fn collect_glyph_bitmaps(
-        let mut buffer = Buffer::new_empty(Metrics::new(text.font_size, text.line_height));
+        &mut self,
+        text: &PreparedText,
+        raster_clip: Option<PixelRect>,
+    ) -> Vec<GlyphBitmap> {
+        let mut buffer = Buffer::new_empty(Metrics::new(
+            text.font_size * self.scale_factor,
+            text.line_height * self.scale_factor,
+        ));
         {
             let mut borrowed = buffer.borrow_with(&mut self.font_system);
             borrowed.set_size(
-                text.bounds.map(|bounds| bounds.width),
+                text.bounds.map(|bounds| bounds.width * self.scale_factor),
-                text.bounds.map(|bounds| bounds.height),
+                text.bounds.map(|bounds| bounds.height * self.scale_factor),
             );
             borrowed.set_text(&text.text, &Attrs::new(), Shaping::Advanced, None);
         }
 
         let mut glyphs = Vec::new();
         for run in buffer.layout_runs() {
+            if let Some(clip) = raster_clip {
+                let line_top = run.line_top.floor() as i32;
+                let line_bottom = (run.line_top + run.line_height).ceil() as i32;
+                if line_bottom < clip.top || line_top > clip.bottom {
+                    continue;
+                }
+            }
             for glyph in run.glyphs {
                 let physical = glyph.physical((0.0, run.line_y), 1.0);
                 let Some(image) = self
@@ -999,13 +1121,17 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
                 if width == 0 || height == 0 {
                     continue;
                 }
+                let rect = PixelRect {
+                    left: physical.x + image.placement.left,
+                    top: physical.y - image.placement.top,
+                    right: physical.x + image.placement.left + width,
+                    bottom: physical.y - image.placement.top + height,
+                };
+                if raster_clip.is_some_and(|clip| !pixel_rects_intersect(rect, clip)) {
+                    continue;
+                }
                 glyphs.push(GlyphBitmap {
-                    rect: PixelRect {
+                    rect,
-                        left: physical.x + image.placement.left,
-                        top: physical.y - image.placement.top,
-                        right: physical.x + image.placement.left + width,
-                        bottom: physical.y - image.placement.top + height,
-                    },
                     content: image.content,
                     color: glyph
                         .color_opt
@@ -1020,6 +1146,7 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
     fn prepare_uploaded_atlas_text(
         &mut self,
         scene: &SceneSnapshot,
+        logical_size: UiSize,
         perf: &mut AtlasTextPerfStats,
     ) -> Option<UploadedAtlasText> {
         let mut vertices = Vec::new();
@@ -1053,7 +1180,8 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
                     if active_clip.rect_active && logical_clip_rect.is_none() {
                         continue;
                     }
-                    let clip_rect = logical_clip_rect.map(rect_to_pixel_rect);
+                    let clip_rect = logical_clip_rect
+                        .map(|rect| scale_rect_to_pixel_rect(rect, self.scale_factor));
 
                     // Only iterate glyphs whose lines fall within the clip rect.
                     // For large text nodes (e.g. full Cargo.lock) this reduces
@@ -1064,7 +1192,10 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
                     perf.glyphs_clip_culled += (all_count - visible.len()) as u32;
 
                     for glyph in visible {
-                        let Some(cache_key) = glyph.cache_key else {
+                        let Some(cache_key) = glyph
+                            .cache_key
+                            .map(|cache_key| scale_glyph_cache_key(cache_key, self.scale_factor))
+                        else {
                             continue;
                         };
                         let resolved_color = resolve_glyph_color(glyph.color, text.default_color);
@@ -1073,9 +1204,12 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
                             continue;
                         };
 
-                        // Glyph positions are LOCAL; add text.origin for absolute screen coords.
+                        // Atlas glyphs are rasterized in device pixels while scene geometry remains
-                        let abs_x = (text.origin.x + glyph.position.x).round() as i32;
+                        // logical. Build and clip in device space, then convert back for vertices.
-                        let abs_y = (text.origin.y + glyph.position.y).round() as i32;
+                        let abs_x =
+                            ((text.origin.x + glyph.position.x) * self.scale_factor).round() as i32;
+                        let abs_y =
+                            ((text.origin.y + glyph.position.y) * self.scale_factor).round() as i32;
                         let glyph_rect = PixelRect {
                             left: abs_x + atlas_glyph.placement_left,
                             top: abs_y - atlas_glyph.placement_top,
@@ -1090,9 +1224,12 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
                             glyph_rect,
                             atlas_glyph.atlas_rect,
                             clip_rect,
-                            scene.logical_size,
+                            GlyphVertexContext {
-                            resolved_color,
+                                logical_size,
-                            active_clip,
+                                scale_factor: self.scale_factor,
+                                color: resolved_color,
+                                clip: active_clip,
+                            },
                         );
                     }
                 }
@@ -1263,9 +1400,10 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
         logical_size: UiSize,
         clip: ActiveClip,
     ) -> Option<UploadedText> {
-        let key = text_texture_key(text);
+        let raster_clip = text_raster_clip(text, clip, logical_size)?;
+        let key = text_texture_key(text, raster_clip, self.scale_factor);
         if !self.text_cache.contains_key(&key) {
-            let rasterized = self.rasterize_text(text)?;
+            let rasterized = self.rasterize_text(text, raster_clip)?;
             let cached = self.create_cached_text_texture(&rasterized);
             self.text_cache.insert(key.clone(), cached);
         }
@@ -1333,8 +1471,8 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
         let texture = self.device.create_texture(&wgpu::TextureDescriptor {
             label: Some("ruin-ui-renderer-wgpu-texture"),
             size: wgpu::Extent3d {
-                width: text.size.width as u32,
+                width: text.texture_size.width as u32,
-                height: text.size.height as u32,
+                height: text.texture_size.height as u32,
                 depth_or_array_layers: 1,
             },
             mip_level_count: 1,
@@ -1354,12 +1492,12 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
             &text.pixels,
             wgpu::TexelCopyBufferLayout {
                 offset: 0,
-                bytes_per_row: Some(text.size.width as u32 * 4),
+                bytes_per_row: Some(text.texture_size.width as u32 * 4),
-                rows_per_image: Some(text.size.height as u32),
+                rows_per_image: Some(text.texture_size.height as u32),
             },
             wgpu::Extent3d {
-                width: text.size.width as u32,
+                width: text.texture_size.width as u32,
-                height: text.size.height as u32,
+                height: text.texture_size.height as u32,
                 depth_or_array_layers: 1,
             },
         );
@@ -1382,7 +1520,7 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
             _texture: texture,
             bind_group,
             origin_offset: text.origin_offset,
-            size: text.size,
+            size: text.draw_size,
         }
     }
 
@@ -1813,32 +1951,44 @@ fn build_textured_vertices(
     ])
 }
 
+#[allow(dead_code)]
+#[derive(Clone, Copy)]
+struct GlyphVertexContext {
+    logical_size: UiSize,
+    scale_factor: f32,
+    color: Color,
+    clip: ActiveClip,
+}
+
 #[allow(dead_code)]
 fn push_glyph_vertices(
     vertices: &mut Vec<TextVertex>,
     glyph_rect: PixelRect,
     atlas_rect: AtlasRect,
     clip_rect: Option<PixelRect>,
-    logical_size: UiSize,
+    context: GlyphVertexContext,
-    color: Color,
-    clip: ActiveClip,
 ) {
     let Some((dest_rect, uv_rect)) = clipped_glyph_quad(glyph_rect, atlas_rect, clip_rect) else {
         return;
     };
 
-    let left = to_ndc_x(dest_rect.left as f32, logical_size.width.max(1.0));
+    let scale_factor = context.scale_factor.max(1.0);
-    let right = to_ndc_x(dest_rect.right as f32, logical_size.width.max(1.0));
+    let logical_left = dest_rect.left as f32 / scale_factor;
-    let top = to_ndc_y(dest_rect.top as f32, logical_size.height.max(1.0));
+    let logical_top = dest_rect.top as f32 / scale_factor;
-    let bottom = to_ndc_y(dest_rect.bottom as f32, logical_size.height.max(1.0));
+    let logical_right = dest_rect.right as f32 / scale_factor;
+    let logical_bottom = dest_rect.bottom as f32 / scale_factor;
+    let left = to_ndc_x(logical_left, context.logical_size.width.max(1.0));
+    let right = to_ndc_x(logical_right, context.logical_size.width.max(1.0));
+    let top = to_ndc_y(logical_top, context.logical_size.height.max(1.0));
+    let bottom = to_ndc_y(logical_bottom, context.logical_size.height.max(1.0));
 
-    let color = color_to_f32(color);
+    let color = color_to_f32(context.color);
-    let clip_rect = clip_rect_array(clip);
+    let clip_rect = clip_rect_array(context.clip);
-    let (rounded_clip_rect, clip_params) = rounded_clip_arrays(clip);
+    let (rounded_clip_rect, clip_params) = rounded_clip_arrays(context.clip);
     vertices.extend_from_slice(&[
         TextVertex {
             position: [left, top],
-            world_position: [dest_rect.left as f32, dest_rect.top as f32],
+            world_position: [logical_left, logical_top],
             uv: [uv_rect.0, uv_rect.1],
             color,
             clip_rect,
@@ -1847,7 +1997,7 @@ fn push_glyph_vertices(
         },
         TextVertex {
             position: [left, bottom],
-            world_position: [dest_rect.left as f32, dest_rect.bottom as f32],
+            world_position: [logical_left, logical_bottom],
             uv: [uv_rect.0, uv_rect.3],
             color,
             clip_rect,
@@ -1856,7 +2006,7 @@ fn push_glyph_vertices(
         },
         TextVertex {
             position: [right, top],
-            world_position: [dest_rect.right as f32, dest_rect.top as f32],
+            world_position: [logical_right, logical_top],
             uv: [uv_rect.2, uv_rect.1],
             color,
             clip_rect,
@@ -1865,7 +2015,7 @@ fn push_glyph_vertices(
         },
         TextVertex {
             position: [right, top],
-            world_position: [dest_rect.right as f32, dest_rect.top as f32],
+            world_position: [logical_right, logical_top],
             uv: [uv_rect.2, uv_rect.1],
             color,
             clip_rect,
@@ -1874,7 +2024,7 @@ fn push_glyph_vertices(
         },
         TextVertex {
             position: [left, bottom],
-            world_position: [dest_rect.left as f32, dest_rect.bottom as f32],
+            world_position: [logical_left, logical_bottom],
             uv: [uv_rect.0, uv_rect.3],
             color,
             clip_rect,
@@ -1883,7 +2033,7 @@ fn push_glyph_vertices(
         },
         TextVertex {
             position: [right, bottom],
-            world_position: [dest_rect.right as f32, dest_rect.bottom as f32],
+            world_position: [logical_right, logical_bottom],
             uv: [uv_rect.2, uv_rect.3],
             color,
             clip_rect,
@@ -1902,9 +2052,9 @@ fn color_to_f32(color: Color) -> [f32; 4] {
     ]
 }
 
-fn build_vertices(scene: &SceneSnapshot) -> Vec<Vertex> {
+fn build_vertices(scene: &SceneSnapshot, logical_size: UiSize) -> Vec<Vertex> {
-    let width = scene.logical_size.width.max(1.0);
+    let width = logical_size.width.max(1.0);
-    let height = scene.logical_size.height.max(1.0);
+    let height = logical_size.height.max(1.0);
     let mut vertices = Vec::new();
     let mut clip_stack = Vec::new();
     let mut active_clip = ActiveClip::default();
@@ -2157,15 +2307,22 @@ fn expand_rect(rect: Rect, inset: f32) -> Rect {
     )
 }
 
-fn rect_to_pixel_rect(rect: Rect) -> PixelRect {
+fn scale_rect_to_pixel_rect(rect: Rect, scale: f32) -> PixelRect {
     PixelRect {
-        left: rect.origin.x.floor() as i32,
+        left: (rect.origin.x * scale).floor() as i32,
-        top: rect.origin.y.floor() as i32,
+        top: (rect.origin.y * scale).floor() as i32,
-        right: (rect.origin.x + rect.size.width).ceil() as i32,
+        right: ((rect.origin.x + rect.size.width) * scale).ceil() as i32,
-        bottom: (rect.origin.y + rect.size.height).ceil() as i32,
+        bottom: ((rect.origin.y + rect.size.height) * scale).ceil() as i32,
     }
 }
 
+fn pixel_rects_intersect(first: PixelRect, second: PixelRect) -> bool {
+    first.left < second.right
+        && first.right > second.left
+        && first.top < second.bottom
+        && first.bottom > second.top
+}
+
 fn shadow_blur_extent(blur: f32) -> f32 {
     blur.max(0.0) * 2.0
 }
@@ -2225,6 +2382,31 @@ fn intersect_rects(first: Option<Rect>, second: Option<Rect>) -> Option<Rect> {
     }
 }
 
+fn text_raster_clip(
+    text: &PreparedText,
+    clip: ActiveClip,
+    logical_size: UiSize,
+) -> Option<Option<Rect>> {
+    let mut absolute_clip = Some(Rect::new(0.0, 0.0, logical_size.width, logical_size.height));
+    if clip.rect_active {
+        absolute_clip = intersect_rects(absolute_clip, Some(clip.resolved_rect()?));
+    }
+    if let Some(bounds) = text.bounds {
+        let text_bounds = Rect::new(text.origin.x, text.origin.y, bounds.width, bounds.height);
+        absolute_clip = intersect_rects(absolute_clip, Some(text_bounds));
+    }
+    absolute_clip?;
+
+    Some(absolute_clip.map(|rect| {
+        Rect::new(
+            rect.origin.x - text.origin.x,
+            rect.origin.y - text.origin.y,
+            rect.size.width,
+            rect.size.height,
+        )
+    }))
+}
+
 fn empty_clip_rect() -> Rect {
     Rect::new(1.0, 1.0, -1.0, -1.0)
 }
@@ -2334,7 +2516,7 @@ fn clip_visible_glyphs(text: &PreparedText, clip: Option<Rect>) -> &[GlyphInstan
     let local_bottom = local_top + clip.size.height;
 
     // First line whose bottom edge reaches or passes the clip top.
-    let start = lines.partition_point(|l| l.rect.origin.y + l.rect.size.height < local_top);
+    let start = lines.partition_point(|l| l.rect.origin.y + l.rect.size.height <= local_top);
     // First line whose top edge is strictly past the clip bottom.
     let end = lines.partition_point(|l| l.rect.origin.y <= local_bottom);
 
@@ -2347,12 +2529,21 @@ fn clip_visible_glyphs(text: &PreparedText, clip: Option<Rect>) -> &[GlyphInstan
     &text.glyphs[glyph_start..glyph_end.min(text.glyphs.len())]
 }
 
-fn text_texture_key(text: &PreparedText) -> TextTextureKey {
+fn text_texture_key(
+    text: &PreparedText,
+    raster_clip: Option<Rect>,
+    scale_factor: f32,
+) -> TextTextureKey {
     TextTextureKey {
-        text: text.text.clone(),
+        layout_key: text.layout_cache_key(),
-        bounds: text
+        bounds: text.bounds.map(|bounds| {
-            .bounds
+            (
-            .map(|bounds| (bounds.width.to_bits(), bounds.height.to_bits())),
+                (bounds.width * scale_factor).ceil() as i32,
+                (bounds.height * scale_factor).ceil() as i32,
+            )
+        }),
+        clip: raster_clip
+            .map(|clip| pixel_rect_tuple(scale_rect_to_pixel_rect(clip, scale_factor))),
         font_size_bits: text.font_size.to_bits(),
         line_height_bits: text.line_height.to_bits(),
         color: (
@@ -2361,28 +2552,33 @@ fn text_texture_key(text: &PreparedText) -> TextTextureKey {
             text.default_color.b,
             text.default_color.a,
         ),
-        glyphs: text
+    }
-            .glyphs
+}
-            .iter()
+
-            .map(|glyph| TextTextureGlyph {
+fn pixel_rect_tuple(rect: PixelRect) -> (i32, i32, i32, i32) {
-                // Glyph positions are already LOCAL; no subtraction needed.
+    (rect.left, rect.top, rect.right, rect.bottom)
-                local_x_bits: glyph.position.x.to_bits(),
+}
-                local_y_bits: glyph.position.y.to_bits(),
+
-                advance_bits: glyph.advance.to_bits(),
+fn scale_glyph_cache_key(cache_key: CacheKey, scale_factor: f32) -> CacheKey {
-                color: (glyph.color.r, glyph.color.g, glyph.color.b, glyph.color.a),
+    CacheKey {
-                cache_key: glyph.cache_key,
+        font_size_bits: (f32::from_bits(cache_key.font_size_bits) * scale_factor.max(1.0))
-            })
+            .to_bits(),
-            .collect(),
+        ..cache_key
     }
 }
 
 #[cfg(test)]
 mod tests {
     use super::{
-        ActiveClip, blend_rgba, build_text_vertices, build_vertices, clip_rect_array,
+        ActiveClip, AtlasRect, GlyphVertexContext, PixelRect, blend_rgba, build_text_vertices,
-        push_clip_state, rounded_clip_arrays, text_texture_key,
+        build_vertices, clip_rect_array, clip_visible_glyphs, push_clip_state, push_glyph_vertices,
+        rounded_clip_arrays, scale_glyph_cache_key, text_texture_key,
+    };
+    use cosmic_text::{CacheKey, CacheKeyFlags, SubpixelBin, fontdb};
+    use ruin_ui::{
+        ClipRegion, Color, Point, PreparedText, Rect, SceneSnapshot, TextStyle, TextSystem,
+        TextWrap, UiSize,
     };
-    use ruin_ui::{ClipRegion, Color, Point, PreparedText, Rect, SceneSnapshot, UiSize};
 
     #[test]
     fn quad_scenes_expand_to_six_vertices_per_quad() {
@@ -2403,7 +2599,7 @@ mod tests {
             Color::rgb(0xFF, 0xFF, 0xFF),
         ));
 
-        let vertices = build_vertices(&scene);
+        let vertices = build_vertices(&scene, scene.logical_size);
         assert_eq!(vertices.len(), 12);
     }
 
@@ -2435,7 +2631,97 @@ mod tests {
             Color::rgb(0xEE, 0xEE, 0xEE),
         );
 
-        assert_eq!(text_texture_key(&first), text_texture_key(&second));
+        assert_eq!(
+            text_texture_key(&first, None, 1.0),
+            text_texture_key(&second, None, 1.0)
+        );
+    }
+
+    #[test]
+    fn text_texture_key_normalizes_clip_to_device_pixels() {
+        let text = PreparedText::monospace(
+            "scrolling text",
+            Point::new(20.0, 30.0),
+            16.0,
+            8.0,
+            Color::rgb(0xEE, 0xEE, 0xEE),
+        );
+
+        let first = text_texture_key(&text, Some(Rect::new(0.001, 4.001, 80.001, 20.001)), 2.0);
+        let second = text_texture_key(&text, Some(Rect::new(0.002, 4.002, 80.002, 20.002)), 2.0);
+        let different_pixel =
+            text_texture_key(&text, Some(Rect::new(0.6, 4.001, 80.001, 20.001)), 2.0);
+
+        assert_eq!(first, second);
+        assert_ne!(first, different_pixel);
+    }
+
+    #[test]
+    fn clip_visible_glyphs_returns_only_lines_intersecting_clip() {
+        let mut text_system = TextSystem::new();
+        let style = TextStyle::new(16.0, Color::rgb(0xEE, 0xEE, 0xEE))
+            .with_wrap(TextWrap::None)
+            .with_line_height(20.0);
+        let text = text_system.prepare("abcd\nefgh", Point::new(10.0, 20.0), &style);
+        let visible = clip_visible_glyphs(&text, Some(Rect::new(10.0, 40.0, 100.0, 20.0)));
+
+        assert_eq!(visible.len(), 4);
+        assert_eq!(visible[0].text_start, 5);
+        assert_eq!(visible[3].text_end, 9);
+    }
+
+    #[test]
+    fn scale_glyph_cache_key_scales_font_size_only() {
+        let key = CacheKey {
+            font_id: fontdb::ID::dummy(),
+            glyph_id: 42,
+            font_size_bits: 13.0_f32.to_bits(),
+            x_bin: SubpixelBin::One,
+            y_bin: SubpixelBin::Two,
+            font_weight: fontdb::Weight::BOLD,
+            flags: CacheKeyFlags::FAKE_ITALIC,
+        };
+
+        let scaled = scale_glyph_cache_key(key, 2.0);
+
+        assert_eq!(f32::from_bits(scaled.font_size_bits), 26.0);
+        assert_eq!(scaled.font_id, key.font_id);
+        assert_eq!(scaled.glyph_id, key.glyph_id);
+        assert_eq!(scaled.x_bin, key.x_bin);
+        assert_eq!(scaled.y_bin, key.y_bin);
+        assert_eq!(scaled.font_weight, key.font_weight);
+        assert_eq!(scaled.flags, key.flags);
+    }
+
+    #[test]
+    fn scaled_atlas_vertices_convert_device_pixels_to_logical_space() {
+        let mut vertices = Vec::new();
+        push_glyph_vertices(
+            &mut vertices,
+            PixelRect {
+                left: 20,
+                top: 10,
+                right: 40,
+                bottom: 30,
+            },
+            AtlasRect {
+                x: 0,
+                y: 0,
+                width: 20,
+                height: 20,
+            },
+            None,
+            GlyphVertexContext {
+                logical_size: UiSize::new(100.0, 100.0),
+                scale_factor: 2.0,
+                color: Color::rgb(0xFF, 0xFF, 0xFF),
+                clip: ActiveClip::default(),
+            },
+        );
+
+        assert_eq!(vertices.len(), 6);
+        assert_eq!(vertices[0].world_position, [10.0, 5.0]);
+        assert_eq!(vertices[5].world_position, [20.0, 15.0]);
     }
 
     #[test]