Lots of owork on a calculator example, transparency, etc.

Cargo.lock

@@ -150,7 +150,7 @@ dependencies = [
  "anyhow",
  "arrayvec",
  "log",
- "nom",
+ "nom 8.0.0",
  "num-rational",
  "v_frame",
 ]
@@ -253,6 +253,17 @@ version = "1.11.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1e748733b7cbc798e1434b6ac524f0c1ff2ab456fe201501e6497c8417a4fc33"
 
+[[package]]
+name = "calculator"
+version = "0.1.0"
+dependencies = [
+ "meval",
+ "ruin-runtime",
+ "ruin_app",
+ "ruin_ui",
+ "tracing-subscriber",
+]
+
 [[package]]
 name = "cast"
 version = "0.3.0"
@@ -606,6 +617,12 @@ dependencies = [
  "miniz_oxide",
 ]
 
+[[package]]
+name = "fnv"
+version = "1.0.7"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3f9eec918d3f24069decb9af1554cad7c880e2da24a9afd88aca000531ab82c1"
+
 [[package]]
 name = "foldhash"
 version = "0.1.5"
@@ -834,6 +851,17 @@ dependencies = [
  "foldhash 0.2.0",
 ]
 
+[[package]]
+name = "hashbrown"
+version = "0.17.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4f467dd6dccf739c208452f8014c75c18bb8301b050ad1cfb27153803edb0f51"
+dependencies = [
+ "allocator-api2",
+ "equivalent",
+ "foldhash 0.2.0",
+]
+
 [[package]]
 name = "hermit-abi"
 version = "0.5.2"
@@ -1165,6 +1193,16 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "meval"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f79496a5651c8d57cd033c5add8ca7ee4e3d5f7587a4777484640d9cb60392d9"
+dependencies = [
+ "fnv",
+ "nom 1.2.4",
+]
+
 [[package]]
 name = "miniz_oxide"
 version = "0.8.9"
@@ -1226,6 +1264,12 @@ version = "1.0.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "650eef8c711430f1a879fdd01d4745a7deea475becfb90269c06775983bbf086"
 
+[[package]]
+name = "nom"
+version = "1.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a5b8c256fd9471521bcb84c3cdba98921497f1a331cbc15b8030fc63b82050ce"
+
 [[package]]
 name = "nom"
 version = "8.0.0"
@@ -1241,6 +1285,15 @@ version = "0.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "0676bb32a98c1a483ce53e500a81ad9c3d5b3f7c920c28c24e9cb0980d0b5bc8"
 
+[[package]]
+name = "nu-ansi-term"
+version = "0.50.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7957b9740744892f114936ab4a57b3f487491bbeafaf8083688b16841a4240e5"
+dependencies = [
+ "windows-sys",
+]
+
 [[package]]
 name = "num-bigint"
 version = "0.4.6"
@@ -1793,6 +1846,14 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "ruin-reactivity-parsing"
+version = "0.1.0"
+dependencies = [
+ "ruin-runtime",
+ "ruin_reactivity",
+]
+
 [[package]]
 name = "ruin-runtime"
 version = "0.1.0"
@@ -1831,6 +1892,7 @@ dependencies = [
 name = "ruin_reactivity"
 version = "0.1.0"
 dependencies = [
+ "hashbrown 0.17.0",
  "ruin-runtime",
  "tracing",
  "tracing-subscriber",
@@ -2257,6 +2319,18 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "db97caf9d906fbde555dd62fa95ddba9eecfd14cb388e4f491a66d74cd5fb79a"
 dependencies = [
  "once_cell",
+ "valuable",
+]
+
+[[package]]
+name = "tracing-log"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ee855f1f400bd0e5c02d150ae5de3840039a3f54b025156404e34c23c03f47c3"
+dependencies = [
+ "log",
+ "once_cell",
+ "tracing-core",
 ]
 
 [[package]]
@@ -2266,12 +2340,15 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cb7f578e5945fb242538965c2d0b04418d38ec25c79d160cd279bf0731c8d319"
 dependencies = [
  "matchers",
+ "nu-ansi-term",
  "once_cell",
  "regex-automata",
  "sharded-slab",
+ "smallvec",
  "thread_local",
  "tracing",
  "tracing-core",
+ "tracing-log",
 ]
 
 [[package]]
@@ -2336,6 +2413,12 @@ dependencies = [
  "wasm-bindgen",
 ]
 
+[[package]]
+name = "valuable"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba73ea9cf16a25df0c8caa16c51acb937d5712a8429db78a3ee29d5dcacd3a65"
+
 [[package]]
 name = "version_check"
 version = "0.9.5"

LICENSE.txt

@@ -0,0 +1,18 @@
+Copyright 2026 Will Temple
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the “Software”), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software is furnished to do so,
+subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

README.md

@@ -0,0 +1,14 @@
+# RUIN - Rust Native Application Framework
+
+A layered architecture for fast, native, cross-platform applications.
+
+RUIN is a modern asynchronous runtime for interactive Rust applications on personal computers. It has a simple
+threading and scheduling model, fast asynchronous I/O (io_uring on Linux, kqueue on macOS, and IOCP on windows),
+and several libraries to enable building modern, reactive applications.
+
+## Runtime
+
+RUIN's core runtime is provided in [`ruin-runtime`](./lib/runtime/).
+
+The runtime is non-workstealing with no threadpool. When a RUIN application starts, it runs a simple event loop on the
+main thread.

examples/calculator/Cargo.toml

@@ -0,0 +1,15 @@
+[package]
+name = "calculator"
+version = "0.1.0"
+edition = "2021"
+
+[[bin]]
+name = "calculator"
+path = "src/main.rs"
+
+[dependencies]
+ruin_app     = { path = "../../lib/ruin_app" }
+ruin_ui      = { path = "../../lib/ui" }
+ruin-runtime = { path = "../../lib/runtime" }
+meval        = "0.2"
+tracing-subscriber = { version = "0.3", features = ["env-filter"] }

examples/calculator/src/components.rs

@@ -0,0 +1,375 @@
+use ruin_app::prelude::*;
+use ruin_ui::{BoxShadow, BoxShadowKind, Point, TextFontFamily};
+
+use crate::state::{CalcMode, CalcState};
+
+// ---------------------------------------------------------------------------
+// Display panel
+// ---------------------------------------------------------------------------
+
+#[component]
+pub fn Display(state: CalcState) -> impl IntoView {
+    let expression = state.expression.clone();
+    let is_error = state.is_error.clone();
+    let history = state.history.clone();
+
+    let result_color = use_memo({
+        let is_error = is_error.clone();
+        move || {
+            if is_error.get() {
+                Color::rgba(200, 30, 30, 245)
+            } else {
+                Color::rgba(20, 140, 20, 245)
+            }
+        }
+    });
+
+    let result_text = use_memo({
+        let result = state.result.clone();
+        move || {
+            let r = result.get();
+            if r.is_empty() { " ".to_string() } else { format!("= {r}") }
+        }
+    });
+
+    view! {
+        block(
+            padding = 12.0,
+            gap = 8.0,
+            // min_height (content) sized to cover scroll_box + expression + result lines
+            // so the window auto-sizes correctly despite text min-size being 0.
+            // Content: scroll_box(100) + expr_text(31) + result_text(20) + 2×gap(16) = 167
+            min_height = 167.0,
+            align_self = AlignItems::Stretch,
+            align_items = AlignItems::End,
+            background = Color::rgba(255, 255, 255, 200),
+            border_radius = 12.0,
+            border = (1.0, Color::rgba(0, 0, 0, 60)),
+            shadow = BoxShadow::new(Point::new(2.0, 2.0), 8.0, 2.0, Color::rgba(0, 0, 0, 40), BoxShadowKind::Outer),
+        ) {
+            block(flex = 1.0, min_height = 0.0) {}
+
+            // History (oldest at top, newest at bottom, scrollable)
+            scroll_box(
+                height = 100.0,
+                offset_y = state.history_scroll.clone(),
+                align_self = AlignItems::Stretch,
+            ) {
+                column(padding = 4.0, gap = 2.0, align_items = AlignItems::End) {
+                    history.with(|entries| {
+                        entries
+                            .iter()
+                            .rev()
+                            .map(|e| {
+                                let expr = e.expression.clone();
+                                let res = e.result.clone();
+                                let s = state.clone();
+                                let res_for_press = res.clone();
+                                view! {
+                                    button(
+                                        align_self = AlignItems::End,
+                                        padding = 4.0,
+                                        background = Color::rgba(0, 0, 0, 0),
+                                        border_radius = 4.0,
+                                        on_press = move |_| s.use_history_result(res_for_press.clone()),
+                                    ) {
+                                        row(gap = 6.0, align_self = AlignItems::End) {
+                                            text(size = 12.0, color = Color::rgba(0, 0, 0, 200), font_family = TextFontFamily::Monospace, wrap = TextWrap::None, weight = FontWeight::Normal) {
+                                                expr.clone()
+                                            }
+                                            text(size = 12.0, color = Color::rgba(20, 130, 20, 230), font_family = TextFontFamily::Monospace, wrap = TextWrap::None, weight = FontWeight::Normal) {
+                                                format!("= {res}")
+                                            }
+                                        }
+                                    }
+                                }
+                            })
+                            .collect::<Vec<_>>()
+                    })
+                }
+            }
+
+            // Current expression
+            text(
+                size = 26.0,
+                font_family = TextFontFamily::Monospace,
+                color = Color::rgba(0, 0, 0, 245),
+                wrap = TextWrap::None,
+                weight = FontWeight::Normal,
+                pointer_events = false,
+            ) {
+                expression.get()
+            }
+
+            // Result / error line
+            if is_error.get() {
+                view! {
+                    text(
+                        size = 16.0,
+                        font_family = TextFontFamily::Monospace,
+                        color = result_color.get(),
+                        wrap = TextWrap::None,
+                        weight = FontWeight::Normal,
+                        pointer_events = false,
+                    ) {
+                        result_text.get()
+                    }
+                }
+            } else {
+                view! {
+                    block(min_height = 0.0) {}
+                }
+            }
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Mode toggle
+// ---------------------------------------------------------------------------
+
+#[component]
+pub fn ModeToggle(state: CalcState) -> impl IntoView {
+    let mode = state.mode.clone();
+
+    view! {
+        row(gap = 6.0, align_self = AlignItems::Stretch) {
+            toggle_button("Basic", mode.get() == CalcMode::Basic, {
+                let state = state.clone();
+                move || state.toggle_mode()
+            })
+            toggle_button("Scientific", mode.get() == CalcMode::Scientific, {
+                let state = state.clone();
+                move || state.toggle_mode()
+            })
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Button helpers
+// ---------------------------------------------------------------------------
+
+fn calc_button(label: String, bg: Color, on_press: impl Fn() + 'static) -> View {
+    let widget_ref = use_widget_ref::<BlockWidget>();
+    let interaction = use_interaction_state(widget_ref.clone());
+
+    button()
+        .widget_ref(widget_ref)
+        .flex(1.0)
+        .min_width(54.0)
+        // min_height = content height for 20px bold text (20 * 1.2 = 24).
+        // This matches the actual rendered line height so window sizing is accurate
+        // and the text is visually centered by the symmetric 8px top/bottom padding.
+        .min_height(24.0)
+        .padding(Edges::symmetric(8.0, 12.0))
+        .align_items(AlignItems::Center)
+        .background(interactive_background(bg, interaction))
+        .border_radius(8.0)
+        .border((0.5, interactive_border(interaction)))
+        .shadow(interactive_shadow(interaction))
+        .on_press(move |_| on_press())
+        .children(
+            text()
+                .size(20.0)
+                .weight(FontWeight::Bold)
+                .selectable(false)
+                .pointer_events(false)
+                .children(label),
+        )
+}
+
+fn btn_row(buttons: Vec<View>) -> View {
+    row().gap(6.0).children(buttons)
+}
+
+fn toggle_button(label: &'static str, active: bool, on_press: impl Fn() + 'static) -> View {
+    let widget_ref = use_widget_ref::<BlockWidget>();
+    let interaction = use_interaction_state(widget_ref.clone());
+    let base = if active {
+        Color::rgba(60, 100, 220, 180)
+    } else {
+        Color::rgba(255, 255, 255, 90)
+    };
+
+    button()
+        .widget_ref(widget_ref)
+        .flex(1.0)
+        .padding(8.0)
+        .min_height(17.0)
+        .align_items(AlignItems::Center)
+        .background(interactive_background(base, interaction))
+        .border_radius(8.0)
+        .border((0.5, interactive_border(interaction)))
+        .shadow(interactive_shadow(interaction))
+        .on_press(move |_| on_press())
+        .children(
+            text()
+                .size(14.0)
+                .weight(FontWeight::Bold)
+                .selectable(false)
+                .pointer_events(false)
+                .children(label),
+        )
+}
+
+fn interactive_background(base: Color, interaction: InteractionState) -> Color {
+    if interaction.pressed {
+        mix(base, Color::BLACK, 0.22)
+    } else if interaction.hovered {
+        mix(base, Color::WHITE, 0.22)
+    } else {
+        base
+    }
+}
+
+fn interactive_border(interaction: InteractionState) -> Color {
+    if interaction.pressed {
+        Color::rgba(0, 0, 0, 96)
+    } else if interaction.hovered {
+        Color::rgba(0, 0, 0, 72)
+    } else {
+        Color::rgba(0, 0, 0, 35)
+    }
+}
+
+fn interactive_shadow(interaction: InteractionState) -> BoxShadow {
+    if interaction.pressed {
+        BoxShadow::new(
+            Point::new(0.0, 0.0),
+            2.0,
+            0.0,
+            Color::rgba(0, 0, 0, 36),
+            BoxShadowKind::Outer,
+        )
+    } else if interaction.hovered {
+        BoxShadow::new(
+            Point::new(0.0, 3.0),
+            14.0,
+            0.0,
+            Color::rgba(0, 0, 0, 42),
+            BoxShadowKind::Outer,
+        )
+    } else {
+        BoxShadow::new(
+            Point::new(0.0, 1.0),
+            6.0,
+            0.0,
+            Color::rgba(0, 0, 0, 18),
+            BoxShadowKind::Outer,
+        )
+    }
+}
+
+fn mix(base: Color, overlay: Color, amount: f32) -> Color {
+    let amount = amount.clamp(0.0, 1.0);
+    let blend = |from: u8, to: u8| -> u8 {
+        ((from as f32) + ((to as f32) - (from as f32)) * amount).round() as u8
+    };
+
+    Color::rgba(
+        blend(base.r, overlay.r),
+        blend(base.g, overlay.g),
+        blend(base.b, overlay.b),
+        base.a,
+    )
+}
+
+// ---------------------------------------------------------------------------
+// Keypad (basic)
+// ---------------------------------------------------------------------------
+
+#[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_eq  = Color::rgba(160, 230, 160, 160);
+    let bg_fn  = Color::rgba(255, 200, 180, 140);
+
+    macro_rules! digit {
+        ($ch:expr) => {{
+            let s = state.clone();
+            let t = $ch.to_string();
+            let label = t.clone();
+            calc_button(label, bg_num, move || s.input(&t))
+        }};
+    }
+    macro_rules! op {
+        ($ch:expr) => {{
+            let s = state.clone();
+            let t = $ch.to_string();
+            let label = t.clone();
+            calc_button(label, bg_op, move || s.input(&t))
+        }};
+    }
+
+    let clear_btn = {
+        let s = state.clone();
+        calc_button("C".to_string(), bg_fn, move || s.clear())
+    };
+    let paren_btn = {
+        let s = state.clone();
+        calc_button("( )".to_string(), bg_num, move || s.input_paren())
+    };
+    let pct_btn = {
+        let s = state.clone();
+        calc_button("%".to_string(), bg_num, move || s.input("%"))
+    };
+    let bs_btn = {
+        let s = state.clone();
+        calc_button("⌫".to_string(), bg_fn, move || s.backspace())
+    };
+    let dot_btn = {
+        let s = state.clone();
+        calc_button(".".to_string(), bg_num, move || s.input("."))
+    };
+    let eq_btn = {
+        let s = state.clone();
+        calc_button("=".to_string(), bg_eq, move || s.evaluate())
+    };
+
+    view! {
+        column(gap = 6.0, align_self = AlignItems::Stretch) {
+            btn_row(vec![clear_btn, paren_btn, pct_btn, bs_btn])
+            btn_row(vec![digit!('7'), digit!('8'), digit!('9'), op!('÷')])
+            btn_row(vec![digit!('4'), digit!('5'), digit!('6'), op!('×')])
+            btn_row(vec![digit!('1'), digit!('2'), digit!('3'), op!('-')])
+            btn_row(vec![digit!('0'), dot_btn, eq_btn, op!('+')])
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Scientific panel
+// ---------------------------------------------------------------------------
+
+#[component]
+pub fn ScientificPanel(state: CalcState) -> impl IntoView {
+    let bg = Color::rgba(230, 215, 255, 140);
+
+    macro_rules! sci {
+        ($label:expr, $insert:expr) => {{
+            let s = state.clone();
+            let ins: &'static str = $insert;
+            calc_button($label.to_string(), bg, move || s.input(ins))
+        }};
+    }
+
+    let sq_btn = {
+        let s = state.clone();
+        calc_button("x²".to_string(), bg, move || {
+            s.expression.update(|e| {
+                let wrapped = format!("({e})^2");
+                *e = wrapped;
+            });
+        })
+    };
+
+    view! {
+        column(gap = 6.0, align_self = AlignItems::Stretch) {
+            btn_row(vec![sci!("sin(", "sin("), sci!("cos(", "cos("), sci!("tan(", "tan("), sci!("asin(", "asin(")])
+            btn_row(vec![sci!("log(", "log("), sci!("ln(", "ln("), sci!("√(", "√("), sq_btn])
+            btn_row(vec![sci!("xʸ", "^"), sci!("π", "π"), sci!("e", "e"), sci!("fact(", "fact(")])
+        }
+    }
+}

examples/calculator/src/main.rs

@@ -0,0 +1,161 @@
+mod components;
+mod state;
+
+use ruin_app::prelude::*;
+use tracing_subscriber::layer::SubscriberExt;
+use tracing_subscriber::util::SubscriberInitExt;
+use tracing_subscriber::{EnvFilter, fmt};
+
+use components::{Display, Keypad, ModeToggle, ScientificPanel};
+use state::{CalcMode, CalcState};
+
+#[ruin_runtime::async_main]
+async fn main() -> ruin_app::Result<()> {
+    init_tracing();
+
+    App::new()
+        .window(
+            Window::new()
+                .title("Calculator")
+                .app_id("dev.ruin.calculator")
+                .base_color(Color::rgba(255, 255, 255, 80))
+                .resizable(false),
+        )
+        .mount(view! { CalculatorApp() {} })
+        .run()
+        .await
+}
+
+fn init_tracing() {
+    let filter = EnvFilter::try_from_default_env().unwrap_or_else(|_| {
+        EnvFilter::new(
+            "info,ruin_app::resize=trace,ruin_app::interaction=trace,\
+             ruin_ui_platform_wayland::resize=trace,ruin_ui_platform_wayland::perf=debug,\
+             ruin_ui_platform_wayland::event_bridge=trace",
+        )
+    });
+
+    let _ = tracing_subscriber::registry()
+        .with(fmt::layer().with_target(true).without_time())
+        .with(filter)
+        .try_init();
+}
+
+#[component]
+fn CalculatorApp() -> impl IntoView {
+    let state = CalcState::new();
+
+    // ---- Keyboard shortcuts (application-scoped) ----
+
+    for ch in "0123456789.+-*/%()".chars() {
+        let s = state.clone();
+        let display = match ch {
+            '*' => "×",
+            '/' => "÷",
+            _ => "",
+        };
+        let text = if display.is_empty() {
+            ch.to_string()
+        } else {
+            display.to_string()
+        };
+        use_shortcut(Shortcut::new(Key::Character(ch)), 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());
+    }
+    {
+        let s = state.clone();
+        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());
+    }
+    {
+        let s = state.clone();
+        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());
+    }
+
+    // ---- Layout ----
+
+    let mode = state.mode.clone();
+
+    let text_style = PartialTextStyle {
+        color: Some(Color::BLACK),
+        ..Default::default()
+    };
+
+    if mode.get() == CalcMode::Scientific {
+        view! {
+            column(
+                gap = 10.0,
+                padding = 12.0,
+                align_items = AlignItems::Stretch,
+                text_style = text_style,
+            ) {
+                Display(state = state.clone()) {}
+                ModeToggle(state = state.clone()) {}
+                ScientificPanel(state = state.clone()) {}
+                Keypad(state = state.clone()) {}
+            }
+        }
+    } else {
+        view! {
+            column(
+                gap = 10.0,
+                padding = 12.0,
+                align_items = AlignItems::Stretch,
+                text_style = text_style,
+            ) {
+                Display(state = state.clone()) {}
+                ModeToggle(state = state.clone()) {}
+                Keypad(state = state.clone()) {}
+            }
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::cell::RefCell;
+    use std::rc::Rc;
+
+    use super::*;
+
+    #[component]
+    fn StateProbe(slot: Rc<RefCell<Option<CalcState>>>) -> impl IntoView {
+        let state = CalcState::new();
+        *slot.borrow_mut() = Some(state);
+        block().children(())
+    }
+
+    #[test]
+    fn successful_evaluation_replaces_expression_and_preserves_history() {
+        let slot = Rc::new(RefCell::new(None::<CalcState>));
+        let _ = ruin_app::__render_mountable_for_test(&view! {
+            StateProbe(slot = Rc::clone(&slot)) {}
+        });
+
+        let state = slot.borrow().clone().expect("state should be captured");
+        let _ = state.expression.set("2+2".to_string());
+        state.evaluate();
+
+        assert_eq!(state.expression.get(), "4");
+        assert_eq!(state.result.get(), "");
+        assert_eq!(state.is_error.get(), false);
+        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

@@ -0,0 +1,198 @@
+use ruin_app::prelude::*;
+
+type EvalResult = std::result::Result<f64, String>;
+
+// ---------------------------------------------------------------------------
+// Types
+// ---------------------------------------------------------------------------
+
+#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
+pub enum CalcMode {
+    #[default]
+    Basic,
+    Scientific,
+}
+
+#[derive(Clone, Debug)]
+pub struct HistoryEntry {
+    pub expression: String,
+    pub result: String,
+}
+
+// ---------------------------------------------------------------------------
+// State
+// ---------------------------------------------------------------------------
+
+#[derive(Clone)]
+pub struct CalcState {
+    /// The expression currently shown in the input display.
+    pub expression: Signal<String>,
+    /// The result of the last evaluation (or error message). Empty until first `=`.
+    pub result: Signal<String>,
+    /// Whether the last evaluation produced an error.
+    pub is_error: Signal<bool>,
+    /// Past evaluations, newest first.
+    pub history: Signal<Vec<HistoryEntry>>,
+    pub mode: Signal<CalcMode>,
+    /// When true, the next digit/operator input clears the expression first.
+    pub fresh: Signal<bool>,
+    /// Current scroll offset for the history scroll box.
+    pub history_scroll: Signal<f32>,
+}
+
+impl CalcState {
+    pub fn new() -> Self {
+        Self {
+            expression: use_signal(|| String::new()),
+            result: use_signal(|| String::new()),
+            is_error: use_signal(|| false),
+            history: use_signal(|| Vec::new()),
+            mode: use_signal(|| CalcMode::Basic),
+            fresh: use_signal(|| false),
+            history_scroll: use_signal(|| 10_000.0_f32),
+        }
+    }
+
+    /// Append `text` to the expression.  If `fresh` is set (just evaluated),
+    /// clear the expression first so digits don't append to the old result.
+    pub fn input(&self, text: &str) {
+        if self.fresh.get() {
+            // Starting fresh after a result: if it's an operator continue
+            // from the result, otherwise start a new expression.
+            let is_operator = matches!(text, "+" | "-" | "×" | "÷" | "^" | "%");
+            if !is_operator {
+                let _ = self.expression.set(String::new());
+            }
+            let _ = self.fresh.set(false);
+        }
+        self.expression.update(|e| e.push_str(text));
+    }
+
+    /// Delete the last character (or close-paren group) from the expression.
+    pub fn backspace(&self) {
+        if self.fresh.get() {
+            let _ = self.fresh.set(false);
+            let _ = self.expression.set(String::new());
+            return;
+        }
+        self.expression.update(|e| {
+            // Pop a full UTF-8 character
+            let new_len = e
+                .char_indices()
+                .next_back()
+                .map(|(i, _)| i)
+                .unwrap_or(0);
+            e.truncate(new_len);
+        });
+    }
+
+    /// Clear the expression, result, and fresh flag.
+    pub fn clear(&self) {
+        let _ = self.expression.set(String::new());
+        let _ = self.result.set(String::new());
+        let _ = self.is_error.set(false);
+        let _ = self.fresh.set(false);
+    }
+
+    /// Evaluate the current expression, update result, push to history.
+    pub fn evaluate(&self) {
+        let expr = self.expression.with(|e| e.clone());
+        if expr.is_empty() {
+            return;
+        }
+        match evaluate(&expr) {
+            Ok(value) => {
+                let result_str = format_result(value);
+                let _ = self.expression.set(result_str.clone());
+                let _ = self.result.set(String::new());
+                let _ = self.is_error.set(false);
+                self.history.update(|h| {
+                    h.insert(
+                        0,
+                        HistoryEntry {
+                            expression: expr.clone(),
+                            result: result_str,
+                        },
+                    );
+                    h.truncate(50);
+                });
+            }
+            Err(msg) => {
+                let _ = self.result.set(msg);
+                let _ = self.is_error.set(true);
+            }
+        }
+        let _ = self.fresh.set(true);
+        let _ = self.history_scroll.set(10_000.0);
+    }
+
+    /// Set the expression to a previously computed result (e.g., when clicking a history entry).
+    pub fn use_history_result(&self, result: String) {
+        let _ = self.expression.set(result);
+        let _ = self.result.set(String::new());
+        let _ = self.is_error.set(false);
+        let _ = self.fresh.set(false);
+    }
+
+    pub fn toggle_mode(&self) {
+        self.mode.update(|m| {
+            *m = match *m {
+                CalcMode::Basic => CalcMode::Scientific,
+                CalcMode::Scientific => CalcMode::Basic,
+            };
+        });
+    }
+
+    /// Insert the right parenthesis character based on current balance.
+    pub fn input_paren(&self) {
+        let open = self
+            .expression
+            .with(|e| e.chars().filter(|&c| c == '(').count());
+        let close = self
+            .expression
+            .with(|e| e.chars().filter(|&c| c == ')').count());
+        self.input(if open > close { ")" } else { "(" });
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Evaluation
+// ---------------------------------------------------------------------------
+
+/// Evaluate `raw_expr`, preprocessing display symbols to meval-compatible syntax.
+pub fn evaluate(raw_expr: &str) -> EvalResult {
+    let expr = raw_expr
+        .replace('×', "*")
+        .replace('÷', "/")
+        .replace('π', "pi")
+        // √( is inserted by the scientific button; meval knows sqrt
+        .replace("√", "sqrt");
+
+    let mut ctx = meval::Context::new();
+    // Add factorial — only integers 0..=20 to avoid overflow
+    ctx.func("fact", |x: f64| {
+        if x < 0.0 || x.fract() != 0.0 || x > 20.0 {
+            return f64::NAN;
+        }
+        (1..=(x as u64)).product::<u64>() as f64
+    });
+
+    meval::eval_str_with_context(&expr, ctx).map_err(|e| e.to_string())
+}
+
+/// Format an f64 result: use integer display when possible, otherwise up to 10 sig figs.
+fn format_result(value: f64) -> String {
+    if value.is_nan() {
+        return "Error".to_string();
+    }
+    if value.is_infinite() {
+        return if value > 0.0 { "∞".to_string() } else { "-∞".to_string() };
+    }
+    if value.fract() == 0.0 && value.abs() < 1e15 {
+        return format!("{}", value as i64);
+    }
+    // Up to 10 significant figures, strip trailing zeros
+    let s = format!("{:.10}", value);
+    let s = s.trim_end_matches('0').trim_end_matches('.');
+    s.to_string()
+}

examples/reactive_layout_demo/src/main.rs

@@ -101,6 +101,7 @@ async fn run_demo() -> Result<(), Box<dyn Error>> {
                 window.surface_target(),
                 initial_size.width as u32,
                 initial_size.height as u32,
+                ruin_ui::Color::rgb(0x08, 0x0C, 0x14),
             )
             .expect("wgpu renderer should initialize");
             let state = Rc::new(RefCell::new(WorkerState {

examples/text_paragraph_demo/src/main.rs

@@ -795,6 +795,7 @@ async fn main() -> Result<(), Box<dyn Error>> {
             let LayoutSnapshot {
                 scene,
                 interaction_tree: next_interaction_tree,
+                ..
             } = build_snapshot(
                 viewport,
                 version,
@@ -1077,6 +1078,7 @@ async fn main() -> Result<(), Box<dyn Error>> {
             let LayoutSnapshot {
                 scene,
                 interaction_tree: next_interaction_tree,
+                ..
             } = build_snapshot(
                 viewport,
                 version,

examples/wayland_wgpu_demo/src/main.rs

@@ -36,6 +36,7 @@ fn main() -> Result<(), Box<dyn Error>> {
         window.surface_target(),
         scene.logical_size.width as u32,
         scene.logical_size.height as u32,
+        ruin_ui::Color::rgb(0x08, 0x0C, 0x14),
     )?;
 
     println!("Opening RUIN Wayland / wgpu demo window...");

lib/reactivity/Cargo.toml

@@ -5,7 +5,12 @@ edition = "2024"
 
 [dependencies]
 ruin_runtime = { package = "ruin-runtime", path = "../runtime" }
-tracing = { version = "0.1", default-features = false, features = ["std"] }
+tracing = { version = "0.1", default-features = false }
+hashbrown = "0.17"
 
 [dev-dependencies]
-tracing-subscriber = { version = "0.3", default-features = false, features = ["env-filter", "fmt", "std"] }
+tracing-subscriber = { version = "0.3", default-features = false, features = [
+    "env-filter",
+    "fmt",
+    "std",
+] }

lib/reactivity/README.md

@@ -0,0 +1,152 @@
+# RUIN Reactivity - Fine-Grained Reactor
+
+Automatic thread-stack-based reactivity for RUIN-apps.
+
+RUIN Reactivity provides an implementation of fine-grained reactivity primitives
+for dependency tracking and incremental computation. Those primitives are:
+
+- `Cell<T>`: a tracked-state value cell, primitively observable (sometimes
+  called a "signal" in other reactor implementations).
+- `effect`: a primitive observer that runs once, observes its dependencies, and
+  runs again whenever its dependencies change.
+- `Thunk<T>`: a tracked-state recomputable value defined by a closure.
+  Invalidated if any of its dependencies change. A `Thunk` is both an observer
+  and an observable.
+- `Event<T>`: a push-style source of events of type `T`. Supports subscription
+  and cancellation of interest in events.
+
+RUIN reactivity requires the RUIN runtime to function, and cannot be used on
+threads not managed by the RUIN runtime.
+
+RUIN reactivity does not function across thread boundaries. It tracks
+dependencies between entities on the same thread only.
+
+## Examples
+
+### Observe a cell using an effect
+
+```rs
+use std::time::Duration;
+
+use ruin_reactivity::{cell, effect};
+use ruin_runtime::{main, set_timeout};
+
+#[main]
+fn main() {
+    // Creates an observable value. Calling `.get` from within an observer will create a dependency, and calling `.set`
+    // will trigger updates to any dependent observers.
+    let v = cell(5);
+
+    // Creates an observer that prints the value of `v` whenever it changes.
+    // Calling `.leak()` on the effect handle allows it to run for the lifetime of the program without automatically
+    // disposing when dropped.
+    effect({
+        let v = v.clone();
+        move || {
+            println!("v is: {}", v.get());
+        }
+    })
+    .leak();
+
+    // Queue a future to wait 5 seconds and then update `v`. This will trigger
+    // the effect to run again and print the new value.
+    set_timeout(Duration::from_secs(5), {
+        let v = v.clone();
+        move || {
+            v.set(v.get() + 20);
+        }
+    });
+}
+```
+
+### Observe a thunk using an effect
+
+```rs
+use std::time::Duration;
+
+use ruin_reactivity::{cell, effect, thunk};
+use ruin_runtime::{clear_interval, main, set_interval, set_timeout};
+
+#[main]
+fn main() {
+    // Two primitive observable values.
+    let x = cell(5);
+    let y = cell(10);
+
+    // A derived observable value that depends on `x` and `y`. The closure will only run when `x` or `y` change, and the
+    // result will be cached until then.
+    let z = thunk({
+        let x = x.clone();
+        let y = y.clone();
+        move || {
+            println!("calculating z...");
+            x.get() + y.get()
+        }
+    });
+
+    // The effect observes `z`, so it will run whenever `z` changes. Because `z` depends on `x` and `y`, the effect will
+    // run whenever `x` or `y` change.
+    effect({
+        let z = z.clone();
+        move || {
+            println!("z is: {}", z.get());
+        }
+    })
+    .leak();
+
+    // Update `x` and `y` every second. This will trigger the effect to run and print the new value of `z`.
+    let interval = set_interval(Duration::from_secs(1), {
+        let x = x.clone();
+        let y = y.clone();
+        move || {
+            x.update(|value| *value += 1);
+            y.update(|value| *value += 2);
+        }
+    });
+
+    // After 10 seconds, clear the interval to stop updating `x` and `y`. Once the interval is cleared, the queue will
+    // empty and the program will exit since there are no more pending tasks.
+    set_timeout(Duration::from_secs(10), move || {
+        println!("clearing interval...");
+        clear_interval(&interval);
+    });
+}
+```
+
+### Use an event to handle intra-thread messaging
+
+```rs
+use std::{cell::Cell, rc::Rc, time::Duration};
+
+use ruin_reactivity::event;
+use ruin_runtime::{main, queue_future, set_interval, time::sleep};
+
+#[main]
+fn main() {
+    let my_event = event::<String>();
+
+    my_event.subscribe(|message| {
+        println!("got event with message: {message}");
+    });
+
+    // Emit an event every 250ms with an incrementing count.
+    let interval = set_interval(Duration::from_millis(250), {
+        let counter = Rc::new(Cell::new(0));
+        move || {
+            let count = counter.get();
+            my_event.emit(format!("the count is {}", count));
+            counter.set(count + 1);
+        }
+    });
+
+    // After 5 seconds, clear the interval to stop emitting events.
+    queue_future(async move {
+        sleep(Duration::from_secs(5)).await;
+        interval.clear();
+    });
+}
+```
+
+## License
+
+Licensed under the [MIT License](../../LICENSE.txt).

lib/reactivity/examples/readme_md_01.rs

@@ -0,0 +1,31 @@
+use std::time::Duration;
+
+use ruin_reactivity::{cell, effect};
+use ruin_runtime::{main, set_timeout};
+
+#[main]
+fn main() {
+    // Creates an observable value. Calling `.get` from within an observer will create a dependency, and calling `.set`
+    // will trigger updates to any dependent observers.
+    let v = cell(5);
+
+    // Creates an observer that prints the value of `v` whenever it changes.
+    // Calling `.leak()` on the effect handle allows it to run for the lifetime of the program without automatically
+    // disposing when dropped.
+    effect({
+        let v = v.clone();
+        move || {
+            println!("v is: {}", v.get());
+        }
+    })
+    .leak();
+
+    // Queue a future to wait 5 seconds and then update `v`. This will trigger
+    // the effect to run again and print the new value.
+    set_timeout(Duration::from_secs(5), {
+        let v = v.clone();
+        move || {
+            v.set(v.get() + 20);
+        }
+    });
+}

lib/reactivity/examples/readme_md_02.rs

@@ -0,0 +1,49 @@
+use std::time::Duration;
+
+use ruin_reactivity::{cell, effect, thunk};
+use ruin_runtime::{clear_interval, main, set_interval, set_timeout};
+
+#[main]
+fn main() {
+    // Two primitive observable values.
+    let x = cell(5);
+    let y = cell(10);
+
+    // A derived observable value that depends on `x` and `y`. The closure will only run when `x` or `y` change, and the
+    // result will be cached until then.
+    let z = thunk({
+        let x = x.clone();
+        let y = y.clone();
+        move || {
+            println!("calculating z...");
+            x.get() + y.get()
+        }
+    });
+
+    // The effect observes `z`, so it will run whenever `z` changes. Because `z` depends on `x` and `y`, the effect will
+    // run whenever `x` or `y` change.
+    effect({
+        let z = z.clone();
+        move || {
+            println!("z is: {}", z.get());
+        }
+    })
+    .leak();
+
+    // Update `x` and `y` every second. This will trigger the effect to run and print the new value of `z`.
+    let interval = set_interval(Duration::from_secs(1), {
+        let x = x.clone();
+        let y = y.clone();
+        move || {
+            x.update(|value| *value += 1);
+            y.update(|value| *value += 2);
+        }
+    });
+
+    // After 10 seconds, clear the interval to stop updating `x` and `y`. Once the interval is cleared, the queue will
+    // empty and the program will exit since there are no more pending tasks.
+    set_timeout(Duration::from_secs(10), move || {
+        println!("clearing interval...");
+        clear_interval(&interval);
+    });
+}

lib/reactivity/examples/readme_md_03.rs

@@ -0,0 +1,29 @@
+use std::{cell::Cell, rc::Rc, time::Duration};
+
+use ruin_reactivity::event;
+use ruin_runtime::{main, queue_future, set_interval, time::sleep};
+
+#[main]
+fn main() {
+    let my_event = event::<String>();
+
+    my_event.subscribe(|message| {
+        println!("got event with message: {message}");
+    });
+
+    // Emit an event every 250ms with an incrementing count.
+    let interval = set_interval(Duration::from_millis(250), {
+        let counter = Rc::new(Cell::new(0));
+        move || {
+            let count = counter.get();
+            my_event.emit(format!("the count is {}", count));
+            counter.set(count + 1);
+        }
+    });
+
+    // After 5 seconds, clear the interval to stop emitting events.
+    queue_future(async move {
+        sleep(Duration::from_secs(5)).await;
+        interval.clear();
+    });
+}

lib/reactivity/src/cell.rs

@@ -1,5 +1,5 @@
-use std::cell::RefCell;
-use std::rc::Rc;
+use alloc::rc::Rc;
+use core::cell::RefCell;
 
 use crate::{NodeId, Reactor, current, trace_targets};
 
@@ -114,7 +114,7 @@ impl<T: PartialEq + 'static> Cell<T> {
             return None;
         }
 
-        let previous = std::mem::replace(&mut *current, value);
+        let previous = core::mem::replace(&mut *current, value);
         drop(current);
         tracing::debug!(
             target: trace_targets::CELL,

lib/reactivity/src/effect.rs

@@ -1,10 +1,14 @@
-use std::cell::{Cell, RefCell};
-use std::rc::{Rc, Weak};
+use alloc::boxed::Box;
+use alloc::rc::{Rc, Weak};
+use core::cell::{Cell, RefCell};
 
 use crate::reactor::ObserverHook;
 use crate::{NodeId, Reactor, current, trace_targets};
 
 /// Creates an effect in the current thread's default reactor.
+///
+/// The effect is scheduled immediately and then re-scheduled whenever one of its dependencies
+/// changes.
 pub fn effect(f: impl Fn() + 'static) -> EffectHandle {
     current().effect(f)
 }
@@ -16,6 +20,7 @@ pub fn effect_in(reactor: &Reactor, f: impl Fn() + 'static) -> EffectHandle {
 
 /// Disposable handle for a reactive effect.
 #[derive(Clone)]
+#[must_use = "effects are automatically disposed when dropped, so you must use the handle or explicitly leak it"]
 pub struct EffectHandle {
     inner: Rc<EffectInner>,
 }
@@ -55,6 +60,14 @@ impl EffectHandle {
         Self { inner }
     }
 
+    /// Consumes the effect and leaks it, allowing it to run for the remainder of the program without automatically
+    /// disposing when dropped. Use this for effects that you want to run for the lifetime of the program. You CANNOT
+    /// recover an EffectHandle after calling this method, so be sure to call it on an EffectHandle that you don't need
+    /// to later dispose of.
+    pub fn leak(self) {
+        core::mem::forget(self);
+    }
+
     /// Disposes the effect immediately.
     pub fn dispose(&self) {
         self.inner.dispose();

lib/reactivity/src/event.rs

@@ -1,6 +1,9 @@
-use std::cell::{Cell, RefCell};
-use std::collections::BTreeMap;
-use std::rc::Rc;
+use alloc::boxed::Box;
+use alloc::rc::Rc;
+use alloc::vec::Vec;
+use core::cell::{Cell, RefCell};
+
+use hashbrown::HashMap;
 
 use crate::{NodeId, Reactor, current, trace_targets};
 
@@ -17,11 +20,13 @@ pub fn event_in<T: 'static>(reactor: &Reactor) -> Event<T> {
 }
 
 /// Creates a reactive draining subscription for `event` in the current reactor.
+#[must_use = "subscriptions created with `on` must be used to stay active"]
 pub fn on<T: Clone + 'static>(event: &Event<T>, handler: impl Fn(&T) + 'static) -> Subscription {
     current().on(event, handler)
 }
 
 /// Creates a reactive draining subscription for `event` associated with `reactor`.
+#[must_use = "subscriptions created with `on_in` must be used to stay active"]
 pub fn on_in<T: Clone + 'static>(
     reactor: &Reactor,
     event: &Event<T>,
@@ -49,6 +54,7 @@ impl Reactor {
     }
 
     /// Creates a reactive draining subscription for `event`.
+    #[must_use = "subscriptions created with `on` must be used to stay active"]
     pub fn on<T: Clone + 'static>(
         &self,
         event: &Event<T>,
@@ -103,7 +109,7 @@ impl<T: 'static> Event<T> {
                 reactor,
                 id,
                 next_subscriber: Cell::new(1),
-                subscribers: RefCell::new(BTreeMap::new()),
+                subscribers: RefCell::new(Default::default()),
             }),
         }
     }
@@ -204,7 +210,7 @@ struct EventInner<T> {
     reactor: Reactor,
     id: NodeId,
     next_subscriber: Cell<usize>,
-    subscribers: RefCell<BTreeMap<usize, Rc<SubscriberFn<T>>>>,
+    subscribers: RefCell<HashMap<usize, Rc<SubscriberFn<T>>>>,
 }
 
 struct SubscriptionInner {
@@ -227,11 +233,12 @@ impl SubscriptionInner {
     }
 }
 
-impl Drop for SubscriptionInner {
-    fn drop(&mut self) {
-        self.unsubscribe();
-    }
-}
+// TODO: it's actually kind of hard to use events if subcscriptions have to be manually managed.
+// impl Drop for SubscriptionInner {
+//     fn drop(&mut self) {
+//         self.unsubscribe();
+//     }
+// }
 
 #[cfg(test)]
 mod tests {

lib/reactivity/src/lib.rs

@@ -4,6 +4,11 @@
 //! single-threaded and designed to live on a runtime-managed thread, while async work feeds it
 //! from the edges by updating state or emitting events.
 
+#![feature(thread_local)]
+#![cfg_attr(not(test), no_std)]
+
+extern crate alloc;
+
 pub(crate) mod trace_targets {
     pub const GRAPH: &str = "ruin_reactivity::graph";
     pub const CELL: &str = "ruin_reactivity::cell";
@@ -18,6 +23,7 @@ mod effect;
 mod event;
 mod id;
 mod reactor;
+mod source;
 mod thunk;
 
 pub use cell::{Cell, cell, cell_in};
@@ -25,4 +31,5 @@ pub use effect::{EffectHandle, effect, effect_in};
 pub use event::{Event, Subscription, event, event_in, on, on_in};
 pub use id::NodeId;
 pub use reactor::{ReactCycleError, Reactor, current};
+pub use source::{Source, source, source_in};
 pub use thunk::{Memo, Thunk, memo, memo_by, memo_by_in, memo_in, thunk, thunk_in};

lib/reactivity/src/reactor.rs

@@ -1,9 +1,12 @@
-use std::cell::{Cell, RefCell};
-use std::collections::{BTreeMap, BTreeSet, VecDeque};
-use std::error::Error;
-use std::fmt;
-use std::panic::panic_any;
-use std::rc::{Rc, Weak};
+use alloc::boxed::Box;
+use alloc::collections::VecDeque;
+use alloc::rc::{Rc, Weak};
+use alloc::vec::Vec;
+use core::cell::{Cell, RefCell};
+use core::error::Error;
+use core::fmt;
+
+use hashbrown::{HashMap, HashSet};
 
 use ruin_runtime::queue_microtask;
 
@@ -11,9 +14,8 @@ use crate::{NodeId, trace_targets};
 
 type Job = Box<dyn FnOnce() + 'static>;
 
-thread_local! {
+#[thread_local]
 static CURRENT_REACTOR: RefCell<Weak<ReactorInner>> = const { RefCell::new(Weak::new()) };
-}
 
 /// Returns the current thread's default reactor.
 ///
@@ -28,7 +30,7 @@ pub(crate) trait ObserverHook {
     fn notify(&self);
 }
 
-/// Panic payload emitted when the reactor detects a dependency cycle.
+/// Error type for cycles detected in the reactive graph. Contains the path of nodes that form the cycle.
 #[derive(Clone, Debug, Eq, PartialEq)]
 pub struct ReactCycleError {
     cycle: Vec<NodeId>,
@@ -85,8 +87,7 @@ impl Reactor {
 
     /// Returns the current thread's default reactor.
     pub fn current() -> Self {
-        CURRENT_REACTOR.with(|slot| {
-            if let Some(inner) = slot.borrow().upgrade() {
+        if let Some(inner) = CURRENT_REACTOR.borrow().upgrade() {
             #[cfg(debug_assertions)]
             tracing::trace!(
                 target: trace_targets::GRAPH,
@@ -97,14 +98,13 @@ impl Reactor {
         }
 
         let reactor = Self::new();
-            *slot.borrow_mut() = Rc::downgrade(&reactor.inner);
+        *CURRENT_REACTOR.borrow_mut() = Rc::downgrade(&reactor.inner);
         tracing::debug!(
             target: trace_targets::GRAPH,
             event = "current_reactor_install",
             "installed current thread default reactor"
         );
         reactor
-        })
     }
 
     /// Runs `f` in the dependency-tracking scope of `observer`.
@@ -143,13 +143,9 @@ impl Reactor {
         f()
     }
 
-    /// Records that the currently executing observer depends on `observable`.
-    ///
-    /// # Panics
-    ///
-    /// Panics with [`ReactCycleError`] if `observable` is already being computed in the current
-    /// dependency stack.
-    pub fn observe(&self, observable: NodeId) {
+    /// Attempts to record a dependency on `observable` for the currently running observer, returning an
+    /// error if doing so would create a dependency cycle.
+    pub fn try_observe(&self, observable: NodeId) -> Result<(), ReactCycleError> {
         if self
             .inner
             .active_computations
@@ -170,12 +166,12 @@ impl Reactor {
                 cycle_len = cycle.len(),
                 "reactive cycle detected"
             );
-            panic_any(ReactCycleError::new(cycle));
+            return Err(ReactCycleError::new(cycle));
         }
 
         let current = self.inner.stack.borrow().last().copied();
         let Some(observer) = current else {
-            return;
+            return Ok(());
         };
 
         #[cfg(debug_assertions)]
@@ -199,6 +195,18 @@ impl Reactor {
             .entry(observable)
             .or_default()
             .insert(observer);
+        Ok(())
+    }
+
+    /// Records a dependency on `observable` for the currently running observer.
+    ///
+    /// # Panics
+    ///
+    /// Panics if recording the dependency would create a cycle in the reactive graph.
+    pub fn observe(&self, observable: NodeId) {
+        if let Err(e) = self.try_observe(observable) {
+            panic!("reactive cycle detected: {e}");
+        }
     }
 
     /// Notifies dependents of `observable`.
@@ -344,11 +352,11 @@ impl fmt::Debug for Reactor {
 
 struct ReactorInner {
     next_node: Cell<u64>,
-    dependencies: RefCell<BTreeMap<NodeId, BTreeSet<NodeId>>>,
-    dependents: RefCell<BTreeMap<NodeId, BTreeSet<NodeId>>>,
-    observers: RefCell<BTreeMap<NodeId, Weak<dyn ObserverHook>>>,
+    dependencies: RefCell<HashMap<NodeId, HashSet<NodeId>>>,
+    dependents: RefCell<HashMap<NodeId, HashSet<NodeId>>>,
+    observers: RefCell<HashMap<NodeId, Weak<dyn ObserverHook>>>,
     stack: RefCell<Vec<NodeId>>,
-    active_computations: RefCell<BTreeSet<NodeId>>,
+    active_computations: RefCell<HashSet<NodeId>>,
     pending_jobs: RefCell<VecDeque<Job>>,
     flush_scheduled: Cell<bool>,
 }
@@ -357,11 +365,11 @@ impl ReactorInner {
     fn new() -> Self {
         Self {
             next_node: Cell::new(1),
-            dependencies: RefCell::new(BTreeMap::new()),
-            dependents: RefCell::new(BTreeMap::new()),
-            observers: RefCell::new(BTreeMap::new()),
+            dependencies: RefCell::new(HashMap::new()),
+            dependents: RefCell::new(HashMap::new()),
+            observers: RefCell::new(HashMap::new()),
             stack: RefCell::new(Vec::new()),
-            active_computations: RefCell::new(BTreeSet::new()),
+            active_computations: RefCell::new(HashSet::new()),
             pending_jobs: RefCell::new(VecDeque::new()),
             flush_scheduled: Cell::new(false),
         }
@@ -421,7 +429,7 @@ mod tests {
 
     use ruin_runtime::{queue_task, run};
 
-    use super::{ReactCycleError, Reactor, current};
+    use super::{Reactor, current};
 
     #[test]
     fn current_reactor_is_thread_local_singleton() {
@@ -436,7 +444,11 @@ mod tests {
         let observer = reactor.allocate_node();
         let observable = reactor.allocate_node();
 
-        reactor.run_in_context(observer, || reactor.observe(observable));
+        reactor.run_in_context(observer, || {
+            reactor
+                .try_observe(observable)
+                .expect("should not detect cycle")
+        });
 
         assert_eq!(
             reactor.inner.dependencies.borrow().get(&observer),
@@ -449,7 +461,7 @@ mod tests {
     }
 
     #[test]
-    fn cycle_detection_panics_with_structured_error() {
+    fn cycle_detection_panics_with_expected() {
         let reactor = Reactor::new();
         let a = reactor.allocate_node();
         let b = reactor.allocate_node();
@@ -457,15 +469,26 @@ mod tests {
         let panic = catch_unwind(AssertUnwindSafe(|| {
             reactor.run_in_context(a, || {
                 reactor.observe(b);
-                reactor.run_in_context(b, || reactor.observe(a));
+                reactor.run_in_context(b, || {
+                    reactor.observe(a);
+                });
             });
         }))
         .expect_err("cycle should panic");
 
-        let error = panic
-            .downcast::<ReactCycleError>()
-            .expect("panic payload should be ReactCycleError");
-        assert_eq!(error.cycle(), &[a, b, a]);
+        let Some(cycle_error) = panic.downcast_ref::<String>() else {
+            panic!("panic should be a string");
+        };
+
+        assert!(
+            cycle_error.contains("reactive cycle detected"),
+            "panic should indicate cycle detected"
+        );
+
+        assert!(
+            cycle_error.contains("1 -> 2 -> 1"),
+            "panic should include cycle path"
+        );
     }
 
     #[test]

lib/reactivity/src/source.rs

@@ -0,0 +1,70 @@
+use alloc::rc::Rc;
+
+use crate::{NodeId, Reactor, current, trace_targets};
+
+/// Creates a low-level reactive source node in the current reactor.
+pub fn source() -> Source {
+    current().source()
+}
+
+/// Creates a low-level reactive source node associated with `reactor`.
+pub fn source_in(reactor: &Reactor) -> Source {
+    reactor.source()
+}
+
+/// Low-level observable source node.
+///
+/// `Source` is useful for advanced data structures that want precise control over when reads
+/// observe and writes trigger invalidation without storing their state in a [`crate::Cell`].
+#[derive(Clone)]
+pub struct Source {
+    inner: Rc<SourceInner>,
+}
+
+impl Reactor {
+    /// Creates a low-level source node associated with this reactor.
+    pub fn source(&self) -> Source {
+        Source::new(self.clone())
+    }
+}
+
+impl Source {
+    fn new(reactor: Reactor) -> Self {
+        let id = reactor.allocate_node();
+        tracing::debug!(
+            target: trace_targets::GRAPH,
+            event = "create_source",
+            node_id = id.0,
+            "created low-level reactive source"
+        );
+        Self {
+            inner: Rc::new(SourceInner { reactor, id }),
+        }
+    }
+
+    /// Records a dependency on this source for the currently running observer.
+    pub fn observe(&self) {
+        self.inner.reactor.observe(self.inner.id);
+    }
+
+    /// Triggers this source's dependents.
+    pub fn trigger(&self) {
+        self.inner.reactor.trigger(self.inner.id);
+    }
+
+    /// Returns the source node id.
+    pub fn id(&self) -> NodeId {
+        self.inner.id
+    }
+}
+
+struct SourceInner {
+    reactor: Reactor,
+    id: NodeId,
+}
+
+impl Drop for SourceInner {
+    fn drop(&mut self) {
+        self.reactor.dispose(self.id);
+    }
+}

lib/reactivity/src/thunk.rs

@@ -1,5 +1,6 @@
-use std::cell::{Cell, RefCell};
-use std::rc::Rc;
+use alloc::boxed::Box;
+use alloc::rc::Rc;
+use core::cell::{Cell, RefCell};
 
 use crate::reactor::ObserverHook;
 use crate::{NodeId, Reactor, current, trace_targets};
@@ -428,9 +429,13 @@ mod tests {
         .expect_err("mutually recursive thunks should panic");
 
         let error = panic
-            .downcast::<crate::ReactCycleError>()
-            .expect("panic payload should be ReactCycleError");
-        assert_eq!(error.cycle().len(), 3);
+            .downcast_ref::<String>()
+            .expect("panic should be a string");
+
+        assert!(
+            error.contains("reactive cycle detected"),
+            "panic should indicate cycle detected"
+        );
     }
 
     #[test]

lib/reactivity_parsing/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "ruin-reactivity-parsing"
+version = "0.1.0"
+edition = "2024"
+
+[lib]
+name = "ruin_reactivity_parsing"
+
+[dependencies]
+ruin_reactivity = { path = "../reactivity" }
+
+[dev-dependencies]
+ruin_runtime = { package = "ruin-runtime", path = "../runtime" }

lib/reactivity_parsing/examples/json_reactive_parser.rs

@@ -0,0 +1,745 @@
+use std::env;
+use std::fmt;
+use std::rc::Rc;
+
+use ruin_reactivity::{cell_in, effect_in};
+use ruin_reactivity_parsing::{
+    Anchor, AnchorBias, EditDelta, ReactiveRope, RopeEdit, TextPoint, TextRange,
+};
+use ruin_runtime::{async_main, fs, stdio};
+
+#[derive(Clone, Debug)]
+struct ParseSnapshot {
+    text: String,
+    root_anchor: Anchor,
+    root: AstNode,
+    reused_nodes: usize,
+    total_nodes: usize,
+    diagnostics: Vec<String>,
+}
+
+#[derive(Clone, Debug)]
+struct AstNode {
+    id: u64,
+    kind: JsonKind,
+    local_range: TextRange,
+    children: Vec<AstNode>,
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+enum JsonKind {
+    Object,
+    Array,
+    Pair,
+    String,
+    Number,
+    True,
+    False,
+    Null,
+}
+
+impl fmt::Display for JsonKind {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let label = match self {
+            Self::Object => "object",
+            Self::Array => "array",
+            Self::Pair => "pair",
+            Self::String => "string",
+            Self::Number => "number",
+            Self::True => "true",
+            Self::False => "false",
+            Self::Null => "null",
+        };
+        write!(f, "{label}")
+    }
+}
+
+#[derive(Clone, Debug)]
+struct ParsedNode {
+    kind: JsonKind,
+    range: TextRange,
+    children: Vec<ParsedNode>,
+}
+
+#[derive(Default)]
+struct JsonParser {
+    next_id: u64,
+}
+
+struct Cursor<'a> {
+    text: &'a str,
+    offset: usize,
+}
+
+#[derive(Clone)]
+enum Command {
+    Insert { offset: usize, text: String },
+    Replace { start: usize, end: usize, text: String },
+    ReplaceAll { text: String },
+    Delete { start: usize, end: usize },
+    Print,
+    Help,
+    Quit,
+}
+
+#[async_main]
+async fn main() {
+    let path = env::args()
+        .nth(1)
+        .expect("usage: cargo run -p ruin-reactivity-parsing --example json_reactive_parser -- <path/to/file.json>");
+    let initial_text = fs::read_to_string(&path)
+        .await
+        .expect("json file should be readable");
+
+    let reactor = ruin_reactivity::Reactor::new();
+    let rope = ReactiveRope::from_text(&reactor, &initial_text);
+    let parser = Rc::new(std::cell::RefCell::new(JsonParser::default()));
+
+    let initial_snapshot = parser
+        .borrow_mut()
+        .parse_initial(&rope)
+        .expect("initial JSON should parse");
+    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();
+        let last_delta = last_delta.clone();
+        rope.edit_events().subscribe(move |delta| {
+            let previous = parse_state.get();
+            match parser.borrow_mut().parse_incremental(&rope, &previous, delta) {
+                Ok(next) => {
+                    last_delta.replace(Some(delta.clone()));
+                    parse_state.replace(next);
+                }
+                Err(error) => {
+                    eprintln!("parse error after edit: {error}");
+                    eprintln!(
+                        "note: current text length is {} bytes; use `replace_all <text>` to replace the full document without manual offsets",
+                        rope.len_bytes()
+                    );
+                }
+            }
+        });
+    };
+
+    effect_in(&reactor, {
+        let rope = rope.clone();
+        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()));
+        }
+    })
+    .leak();
+
+    println!("Commands:");
+    println!("  insert <byte_offset> <text>");
+    println!("  replace <start> <end> <text>");
+    println!("  replace_all <text>");
+    println!("  delete <start> <end>");
+    println!("  print");
+    println!("  help");
+    println!("  quit");
+
+    let mut input = stdio::stdin().expect("stdin should be available");
+    while let Some(line) = input.read_line().await.expect("stdin read should succeed") {
+        let trimmed = line.trim_end();
+        if trimmed.is_empty() {
+            continue;
+        }
+
+        match parse_command(trimmed) {
+            Ok(Command::Insert { offset, text }) => {
+                let _ = rope.edit(RopeEdit::insert(offset, text));
+            }
+            Ok(Command::Replace { start, end, text }) => {
+                let _ = rope.edit(RopeEdit::replace(TextRange::new(start, end), text));
+            }
+            Ok(Command::ReplaceAll { text }) => {
+                let _ = rope.edit(RopeEdit::replace(TextRange::new(0, rope.len_bytes()), text));
+            }
+            Ok(Command::Delete { start, end }) => {
+                let _ = rope.edit(RopeEdit::delete(TextRange::new(start, end)));
+            }
+            Ok(Command::Print) => {
+                let snapshot = parse_state.get();
+                print_snapshot(&snapshot, &rope, None);
+            }
+            Ok(Command::Help) => {
+                println!("Commands:");
+                println!("  insert <byte_offset> <text>");
+                println!("  replace <start> <end> <text>");
+                println!("  replace_all <text>");
+                println!("  delete <start> <end>");
+                println!("  print");
+                println!("  help");
+                println!("  quit");
+            }
+            Ok(Command::Quit) => break,
+            Err(error) => eprintln!("{error}"),
+        }
+    }
+}
+
+fn parse_command(input: &str) -> Result<Command, String> {
+    if input == "quit" {
+        return Ok(Command::Quit);
+    }
+    if input == "print" {
+        return Ok(Command::Print);
+    }
+    if input == "help" {
+        return Ok(Command::Help);
+    }
+    if let Some(rest) = input.strip_prefix("insert ") {
+        let (offset, text) = rest
+            .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())?,
+            text: text.to_string(),
+        });
+    }
+    if let Some(rest) = input.strip_prefix("replace ") {
+        let mut parts = rest.splitn(3, ' ');
+        let start = parts
+            .next()
+            .ok_or_else(|| "replace expects: replace <start> <end> <text>".to_string())?;
+        let end = parts
+            .next()
+            .ok_or_else(|| "replace expects: replace <start> <end> <text>".to_string())?;
+        let text = parts
+            .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())?,
+            end: end.parse().map_err(|_| "invalid replace end".to_string())?,
+            text: text.to_string(),
+        });
+    }
+    if let Some(text) = input.strip_prefix("replace_all ") {
+        return Ok(Command::ReplaceAll {
+            text: text.to_string(),
+        });
+    }
+    if let Some(rest) = input.strip_prefix("delete ") {
+        let (start, end) = rest
+            .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())?,
+            end: end.parse().map_err(|_| "invalid delete end".to_string())?,
+        });
+    }
+    Err("unknown command; type `help`".to_string())
+}
+
+impl JsonParser {
+    fn parse_initial(&mut self, rope: &ReactiveRope) -> Result<ParseSnapshot, String> {
+        let text = read_rope_text(rope);
+        let parsed = parse_json(&text)?;
+        let root = self.materialize_fresh(&parsed, 0);
+        Ok(ParseSnapshot {
+            text,
+            root_anchor: Anchor::new(0, AnchorBias::Left),
+            total_nodes: count_nodes(&root),
+            reused_nodes: 0,
+            diagnostics: Vec::new(),
+            root,
+        })
+    }
+
+    fn parse_incremental(
+        &mut self,
+        rope: &ReactiveRope,
+        previous: &ParseSnapshot,
+        delta: &EditDelta,
+    ) -> Result<ParseSnapshot, String> {
+        let text = read_rope_text(rope);
+        let parsed = parse_json(&text)?;
+        let mut root_anchor = previous.root_anchor;
+        root_anchor.map_through(delta);
+        let mut reused = 0usize;
+        let root = self.reuse_node(
+            &parsed,
+            Some(&previous.root),
+            previous.root_anchor.byte,
+            root_anchor.byte,
+            &previous.text,
+            &text,
+            delta,
+            &mut reused,
+        );
+        Ok(ParseSnapshot {
+            text,
+            root_anchor,
+            total_nodes: count_nodes(&root),
+            reused_nodes: reused,
+            diagnostics: Vec::new(),
+            root,
+        })
+    }
+
+    fn materialize_fresh(&mut self, parsed: &ParsedNode, parent_start: usize) -> AstNode {
+        AstNode {
+            id: self.alloc_id(),
+            kind: parsed.kind,
+            local_range: localize(parsed.range, parent_start),
+            children: parsed
+                .children
+                .iter()
+                .map(|child| self.materialize_fresh(child, parsed.range.start))
+                .collect(),
+        }
+    }
+
+    fn reuse_node(
+        &mut self,
+        parsed: &ParsedNode,
+        old: Option<&AstNode>,
+        old_parent_start: usize,
+        new_parent_start: usize,
+        old_text: &str,
+        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
+            && old_text
+                .get(absolute_range(old, old_parent_start).start..absolute_range(old, old_parent_start).end)
+                == new_text.get(parsed.range.start..parsed.range.end)
+        {
+            *reused += count_nodes(old);
+            return AstNode {
+                id: old.id,
+                kind: old.kind,
+                local_range: parsed_local,
+                children: old.children.clone(),
+            };
+        }
+
+        let children = parsed
+            .children
+            .iter()
+            .enumerate()
+            .map(|(index, child)| {
+                let previous_child = old.and_then(|node| node.children.get(index));
+                let next_old_parent_start = old
+                    .map(|node| absolute_range(node, old_parent_start).start)
+                    .unwrap_or(old_parent_start);
+                self.reuse_node(
+                    child,
+                    previous_child,
+                    next_old_parent_start,
+                    parsed.range.start,
+                    old_text,
+                    new_text,
+                    delta,
+                    reused,
+                )
+            })
+            .collect();
+
+        AstNode {
+            id: self.alloc_id(),
+            kind: parsed.kind,
+            local_range: parsed_local,
+            children,
+        }
+    }
+
+    fn alloc_id(&mut self) -> u64 {
+        self.next_id = self.next_id.wrapping_add(1);
+        self.next_id
+    }
+}
+
+fn read_rope_text(rope: &ReactiveRope) -> String {
+    let mut cursor = rope.cursor(0);
+    let mut text = String::new();
+    while let Some(chunk) = cursor.next_chunk() {
+        text.push_str(chunk.text());
+    }
+    text
+}
+
+fn localize(range: TextRange, parent_start: usize) -> TextRange {
+    TextRange::new(
+        range.start.saturating_sub(parent_start),
+        range.end.saturating_sub(parent_start),
+    )
+}
+
+fn absolute_range(node: &AstNode, parent_start: usize) -> TextRange {
+    TextRange::new(
+        parent_start + node.local_range.start,
+        parent_start + node.local_range.end,
+    )
+}
+
+fn map_range(range: TextRange, delta: &EditDelta) -> TextRange {
+    if range.end <= delta.range.start {
+        return range;
+    }
+    if range.start >= delta.range.end {
+        let shift = delta.net_byte_delta();
+        return TextRange::new(
+            range.start.saturating_add_signed(shift),
+            range.end.saturating_add_signed(shift),
+        );
+    }
+    TextRange::new(usize::MAX, usize::MAX)
+}
+
+fn parse_json(text: &str) -> Result<ParsedNode, String> {
+    let mut cursor = Cursor { text, offset: 0 };
+    cursor.skip_ws();
+    let node = cursor.parse_value()?;
+    cursor.skip_ws();
+    if !cursor.is_eof() {
+        return Err(format!("unexpected trailing data at byte {}", cursor.offset));
+    }
+    Ok(node)
+}
+
+impl<'a> Cursor<'a> {
+    fn is_eof(&self) -> bool {
+        self.offset >= self.text.len()
+    }
+
+    fn skip_ws(&mut self) {
+        while let Some(ch) = self.peek_char() {
+            if ch.is_ascii_whitespace() {
+                self.offset += ch.len_utf8();
+            } else {
+                break;
+            }
+        }
+    }
+
+    fn peek_char(&self) -> Option<char> {
+        self.text[self.offset..].chars().next()
+    }
+
+    fn bump_char(&mut self) -> Option<char> {
+        let ch = self.peek_char()?;
+        self.offset += ch.len_utf8();
+        Some(ch)
+    }
+
+    fn expect_char(&mut self, expected: char) -> Result<(), String> {
+        match self.bump_char() {
+            Some(ch) if ch == expected => Ok(()),
+            Some(ch) => Err(format!(
+                "expected `{expected}` at byte {}, found `{ch}`",
+                self.offset.saturating_sub(ch.len_utf8())
+            )),
+            None => Err(format!("expected `{expected}` at end of file")),
+        }
+    }
+
+    fn parse_value(&mut self) -> Result<ParsedNode, String> {
+        self.skip_ws();
+        match self.peek_char() {
+            Some('{') => self.parse_object(),
+            Some('[') => self.parse_array(),
+            Some('"') => self.parse_string(),
+            Some('t') => self.parse_literal("true", JsonKind::True),
+            Some('f') => self.parse_literal("false", JsonKind::False),
+            Some('n') => self.parse_literal("null", JsonKind::Null),
+            Some('-' | '0'..='9') => self.parse_number(),
+            Some(other) => Err(format!("unexpected `{other}` at byte {}", self.offset)),
+            None => Err("unexpected end of JSON input".to_string()),
+        }
+    }
+
+    fn parse_object(&mut self) -> Result<ParsedNode, String> {
+        let start = self.offset;
+        self.expect_char('{')?;
+        self.skip_ws();
+        let mut children = Vec::new();
+        if self.peek_char() == Some('}') {
+            self.bump_char();
+            return Ok(ParsedNode {
+                kind: JsonKind::Object,
+                range: TextRange::new(start, self.offset),
+                children,
+            });
+        }
+
+        loop {
+            self.skip_ws();
+            let key = self.parse_string()?;
+            self.skip_ws();
+            self.expect_char(':')?;
+            self.skip_ws();
+            let value = self.parse_value()?;
+            let pair = ParsedNode {
+                kind: JsonKind::Pair,
+                range: TextRange::new(key.range.start, value.range.end),
+                children: vec![key, value],
+            };
+            children.push(pair);
+            self.skip_ws();
+            match self.peek_char() {
+                Some(',') => {
+                    self.bump_char();
+                }
+                Some('}') => {
+                    self.bump_char();
+                    break;
+                }
+                Some(other) => {
+                    return Err(format!("expected `,` or `}}` at byte {}, found `{other}`", self.offset));
+                }
+                None => return Err("unterminated object".to_string()),
+            }
+        }
+
+        Ok(ParsedNode {
+            kind: JsonKind::Object,
+            range: TextRange::new(start, self.offset),
+            children,
+        })
+    }
+
+    fn parse_array(&mut self) -> Result<ParsedNode, String> {
+        let start = self.offset;
+        self.expect_char('[')?;
+        self.skip_ws();
+        let mut children = Vec::new();
+        if self.peek_char() == Some(']') {
+            self.bump_char();
+            return Ok(ParsedNode {
+                kind: JsonKind::Array,
+                range: TextRange::new(start, self.offset),
+                children,
+            });
+        }
+
+        loop {
+            let value = self.parse_value()?;
+            children.push(value);
+            self.skip_ws();
+            match self.peek_char() {
+                Some(',') => {
+                    self.bump_char();
+                    self.skip_ws();
+                }
+                Some(']') => {
+                    self.bump_char();
+                    break;
+                }
+                Some(other) => {
+                    return Err(format!("expected `,` or `]` at byte {}, found `{other}`", self.offset));
+                }
+                None => return Err("unterminated array".to_string()),
+            }
+        }
+
+        Ok(ParsedNode {
+            kind: JsonKind::Array,
+            range: TextRange::new(start, self.offset),
+            children,
+        })
+    }
+
+    fn parse_string(&mut self) -> Result<ParsedNode, String> {
+        let start = self.offset;
+        self.expect_char('"')?;
+        loop {
+            match self.bump_char() {
+                Some('"') => {
+                    return Ok(ParsedNode {
+                        kind: JsonKind::String,
+                        range: TextRange::new(start, self.offset),
+                        children: Vec::new(),
+                    });
+                }
+                Some('\\') => match self.bump_char() {
+                    Some('"') | Some('\\') | Some('/') | Some('b') | Some('f') | Some('n')
+                    | Some('r') | Some('t') => {}
+                    Some('u') => {
+                        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 escape sequence at byte {}", self.offset)),
+                },
+                Some(ch) if ch >= '\u{20}' => {}
+                Some(_) => return Err(format!("control character in string at byte {}", self.offset)),
+                None => return Err("unterminated string".to_string()),
+            }
+        }
+    }
+
+    fn parse_number(&mut self) -> Result<ParsedNode, String> {
+        let start = self.offset;
+        if self.peek_char() == Some('-') {
+            self.bump_char();
+        }
+
+        match self.peek_char() {
+            Some('0') => {
+                self.bump_char();
+            }
+            Some('1'..='9') => {
+                self.bump_char();
+                while matches!(self.peek_char(), Some('0'..='9')) {
+                    self.bump_char();
+                }
+            }
+            _ => return Err(format!("invalid number at byte {}", self.offset)),
+        }
+
+        if self.peek_char() == Some('.') {
+            self.bump_char();
+            let mut digits = 0usize;
+            while matches!(self.peek_char(), Some('0'..='9')) {
+                digits += 1;
+                self.bump_char();
+            }
+            if digits == 0 {
+                return Err(format!("expected fraction digits at byte {}", self.offset));
+            }
+        }
+
+        if matches!(self.peek_char(), Some('e' | 'E')) {
+            self.bump_char();
+            if matches!(self.peek_char(), Some('+' | '-')) {
+                self.bump_char();
+            }
+            let mut digits = 0usize;
+            while matches!(self.peek_char(), Some('0'..='9')) {
+                digits += 1;
+                self.bump_char();
+            }
+            if digits == 0 {
+                return Err(format!("expected exponent digits at byte {}", self.offset));
+            }
+        }
+
+        Ok(ParsedNode {
+            kind: JsonKind::Number,
+            range: TextRange::new(start, self.offset),
+            children: Vec::new(),
+        })
+    }
+
+    fn parse_literal(&mut self, literal: &str, kind: JsonKind) -> Result<ParsedNode, String> {
+        let start = self.offset;
+        if !self.text[self.offset..].starts_with(literal) {
+            return Err(format!("expected `{literal}` at byte {}", self.offset));
+        }
+        self.offset += literal.len();
+        Ok(ParsedNode {
+            kind,
+            range: TextRange::new(start, self.offset),
+            children: Vec::new(),
+        })
+    }
+}
+
+fn print_snapshot(snapshot: &ParseSnapshot, rope: &ReactiveRope, delta: Option<&EditDelta>) {
+    let metrics = rope.snapshot_metrics();
+    println!();
+    println!("Document revision {}", metrics.revision);
+    println!(
+        "Text bytes={}, leaves={}, nodes={}, reused_on_last_edit={}",
+        metrics.text.bytes, metrics.leaves, snapshot.total_nodes, snapshot.reused_nodes
+    );
+    if let Some(delta) = delta {
+        println!(
+            "Last edit: [{}..{}) -> {:?}",
+            delta.range.start, delta.range.end, delta.inserted_text
+        );
+        let focus = delta.range.start.min(snapshot.text.len().saturating_sub(1));
+        let path = path_for_offset(&snapshot.root, snapshot.root_anchor.byte, focus);
+        println!("Changed path:");
+        for (node, range) in path {
+            let start = rope.point_at(range.start);
+            let end = rope.point_at(range.end);
+            println!(
+                "  id={} kind={} span={}",
+                node.id,
+                node.kind,
+                format_span(start, end)
+            );
+        }
+    }
+    if !snapshot.diagnostics.is_empty() {
+        println!("Diagnostics:");
+        for diagnostic in &snapshot.diagnostics {
+            println!("  - {diagnostic}");
+        }
+    }
+    println!("Root id={} kind={}", snapshot.root.id, snapshot.root.kind);
+    println!("Parse tree:");
+    print_tree(&snapshot.root, snapshot.root_anchor.byte, rope, 0);
+    println!("Current text:");
+    println!("{}", snapshot.text);
+}
+
+fn print_tree(node: &AstNode, parent_start: usize, rope: &ReactiveRope, depth: usize) {
+    let range = absolute_range(node, parent_start);
+    let start = rope.point_at(range.start);
+    let end = rope.point_at(range.end);
+    let indent = "  ".repeat(depth);
+    println!(
+        "{indent}- id={} kind={} span={}",
+        node.id,
+        node.kind,
+        format_span(start, end)
+    );
+    for child in &node.children {
+        print_tree(child, range.start, rope, depth + 1);
+    }
+}
+
+fn path_for_offset(root: &AstNode, root_start: usize, offset: usize) -> Vec<(&AstNode, TextRange)> {
+    fn walk<'a>(
+        node: &'a AstNode,
+        parent_start: usize,
+        offset: usize,
+        out: &mut Vec<(&'a AstNode, TextRange)>,
+    ) -> bool {
+        let range = absolute_range(node, parent_start);
+        if offset < range.start || offset >= range.end {
+            return false;
+        }
+        out.push((node, range));
+        for child in &node.children {
+            if walk(child, range.start, offset, out) {
+                return true;
+            }
+        }
+        true
+    }
+
+    let mut path = Vec::new();
+    let _ = walk(root, root_start, offset, &mut path);
+    path
+}
+
+fn format_span(start: TextPoint, end: TextPoint) -> String {
+    format!(
+        "{}:{}..{}:{}",
+        start.line + 1,
+        start.column + 1,
+        end.line + 1,
+        end.column + 1
+    )
+}
+
+fn count_nodes(node: &AstNode) -> usize {
+    1 + node.children.iter().map(count_nodes).sum::<usize>()
+}

lib/reactivity_parsing/examples/tokentree_reactive_parser.rs

@@ -0,0 +1,207 @@
+use std::env;
+use std::rc::Rc;
+
+use ruin_reactivity::effect_in;
+use ruin_reactivity_parsing::{
+    ReactiveRope, ReactiveTokenTree, RopeEdit, TextRange, TokenTreeNode, TokenTreeParse,
+    TokenTreeUpdate,
+};
+use ruin_runtime::{async_main, fs, stdio};
+
+enum Command {
+    Insert { offset: usize, text: String },
+    Replace { start: usize, end: usize, text: String },
+    ReplaceAll { text: String },
+    Delete { start: usize, end: usize },
+    Print,
+    Help,
+    Quit,
+}
+
+#[async_main]
+async fn main() {
+    let path = env::args()
+        .nth(1)
+        .expect("usage: cargo run -p ruin-reactivity-parsing --example tokentree_reactive_parser -- <path/to/file>");
+    let initial_text = fs::read_to_string(&path)
+        .await
+        .expect("source file should be readable");
+
+    let reactor = ruin_reactivity::Reactor::new();
+    let rope = ReactiveRope::from_text(&reactor, &initial_text);
+    let parser = Rc::new(ReactiveTokenTree::new(&rope));
+
+    effect_in(&reactor, {
+        let parser = Rc::clone(&parser);
+        let rope = rope.clone();
+        move || {
+            parser.with_snapshot(|snapshot| {
+                let last_update = parser.last_update();
+                print_snapshot(snapshot, &rope, last_update.as_ref());
+            });
+        }
+    })
+    .leak();
+
+    println!("Commands:");
+    println!("  insert <byte_offset> <text>");
+    println!("  replace <start> <end> <text>");
+    println!("  replace_all <text>");
+    println!("  delete <start> <end>");
+    println!("  print");
+    println!("  help");
+    println!("  quit");
+
+    let mut input = stdio::stdin().expect("stdin should be available");
+    while let Some(line) = input.read_line().await.expect("stdin read should succeed") {
+        let trimmed = line.trim_end();
+        if trimmed.is_empty() {
+            continue;
+        }
+
+        match parse_command(trimmed) {
+            Ok(Command::Insert { offset, text }) => {
+                let _ = rope.edit(RopeEdit::insert(offset, text));
+            }
+            Ok(Command::Replace { start, end, text }) => {
+                let _ = rope.edit(RopeEdit::replace(TextRange::new(start, end), text));
+            }
+            Ok(Command::ReplaceAll { text }) => {
+                let _ = rope.edit(RopeEdit::replace(TextRange::new(0, rope.len_bytes()), text));
+            }
+            Ok(Command::Delete { start, end }) => {
+                let _ = rope.edit(RopeEdit::delete(TextRange::new(start, end)));
+            }
+            Ok(Command::Print) => {
+                let snapshot = parser.snapshot();
+                let last_update = parser.last_update();
+                print_snapshot(&snapshot, &rope, last_update.as_ref());
+            }
+            Ok(Command::Help) => {
+                println!("Commands:");
+                println!("  insert <byte_offset> <text>");
+                println!("  replace <start> <end> <text>");
+                println!("  replace_all <text>");
+                println!("  delete <start> <end>");
+                println!("  print");
+                println!("  help");
+                println!("  quit");
+            }
+            Ok(Command::Quit) => break,
+            Err(error) => eprintln!("{error}"),
+        }
+    }
+}
+
+fn parse_command(input: &str) -> Result<Command, String> {
+    if input == "quit" {
+        return Ok(Command::Quit);
+    }
+    if input == "print" {
+        return Ok(Command::Print);
+    }
+    if input == "help" {
+        return Ok(Command::Help);
+    }
+    if let Some(rest) = input.strip_prefix("insert ") {
+        let (offset, text) = rest
+            .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())?,
+            text: text.to_string(),
+        });
+    }
+    if let Some(rest) = input.strip_prefix("replace ") {
+        let mut parts = rest.splitn(3, ' ');
+        let start = parts
+            .next()
+            .ok_or_else(|| "replace expects: replace <start> <end> <text>".to_string())?;
+        let end = parts
+            .next()
+            .ok_or_else(|| "replace expects: replace <start> <end> <text>".to_string())?;
+        let text = parts
+            .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())?,
+            end: end.parse().map_err(|_| "invalid replace end".to_string())?,
+            text: text.to_string(),
+        });
+    }
+    if let Some(text) = input.strip_prefix("replace_all ") {
+        return Ok(Command::ReplaceAll {
+            text: text.to_string(),
+        });
+    }
+    if let Some(rest) = input.strip_prefix("delete ") {
+        let (start, end) = rest
+            .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())?,
+            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>) {
+    let metrics = rope.snapshot_metrics();
+    println!();
+    println!("Document revision {}", metrics.revision);
+    println!(
+        "Text bytes={}, leaves={}, nodes={}, reused_on_last_edit={}",
+        metrics.text.bytes,
+        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.end,
+            update.delta.inserted_text
+        );
+        println!(
+            "Diagnostics changed={}, trivia changed={}",
+            update.diagnostics_changed,
+            update.trivia_changed
+        );
+    }
+    println!("Parse tree:");
+    print_tree(snapshot, rope, &snapshot.root, 0);
+    if !snapshot.diagnostics.is_empty() {
+        println!("Diagnostics:");
+        for diagnostic in &snapshot.diagnostics {
+            println!(
+                "  {:?} [{}..{}): {}",
+                diagnostic.kind, diagnostic.range.start, diagnostic.range.end, diagnostic.message
+            );
+        }
+    }
+    if !snapshot.trivia.comments().is_empty() {
+        println!("Comments:");
+        for comment in snapshot.trivia.comments() {
+            println!(
+                "  {:?} [{}..{}): {}",
+                comment.kind, comment.range.start, comment.range.end, comment.text
+            );
+        }
+    }
+}
+
+fn print_tree(snapshot: &TokenTreeParse, rope: &ReactiveRope, node: &TokenTreeNode, depth: usize) {
+    let indent = "  ".repeat(depth);
+    let (start, end) = snapshot
+        .absolute_span(rope, node.id)
+        .expect("node span should be available");
+    println!(
+        "{}- id={} kind={} span=({}:{})..({}:{})",
+        indent, node.id, node.kind, start.line, start.column, end.line, end.column
+    );
+    for child in &node.children {
+        print_tree(snapshot, rope, child, depth + 1);
+    }
+}

lib/reactivity_parsing/src/delta.rs

@@ -0,0 +1,152 @@
+use crate::metrics::{TextMetrics, TextPoint};
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct TextRange {
+    pub start: usize,
+    pub end: usize,
+}
+
+impl TextRange {
+    pub const fn new(start: usize, end: usize) -> Self {
+        Self { start, end }
+    }
+
+    pub const fn len(self) -> usize {
+        self.end - self.start
+    }
+
+    pub const fn is_empty(self) -> bool {
+        self.start == self.end
+    }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct RopeEdit {
+    pub range: TextRange,
+    pub insert: String,
+}
+
+impl RopeEdit {
+    pub fn insert(offset: usize, text: impl Into<String>) -> Self {
+        Self {
+            range: TextRange::new(offset, offset),
+            insert: text.into(),
+        }
+    }
+
+    pub fn delete(range: TextRange) -> Self {
+        Self {
+            range,
+            insert: String::new(),
+        }
+    }
+
+    pub fn replace(range: TextRange, text: impl Into<String>) -> Self {
+        Self {
+            range,
+            insert: text.into(),
+        }
+    }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct EditDelta {
+    pub range: TextRange,
+    pub removed_text: String,
+    pub inserted_text: String,
+    pub removed: TextMetrics,
+    pub inserted: TextMetrics,
+    pub start: TextPoint,
+    pub old_end: TextPoint,
+    pub new_end: TextPoint,
+}
+
+impl EditDelta {
+    pub fn net_byte_delta(&self) -> isize {
+        self.inserted.bytes as isize - self.removed.bytes as isize
+    }
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum AnchorBias {
+    Left,
+    Right,
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct Anchor {
+    pub byte: usize,
+    pub bias: AnchorBias,
+}
+
+impl Anchor {
+    pub const fn new(byte: usize, bias: AnchorBias) -> Self {
+        Self { byte, bias }
+    }
+
+    pub fn map_through(&mut self, delta: &EditDelta) {
+        if self.byte < delta.range.start {
+            return;
+        }
+
+        if self.byte > delta.range.end {
+            self.byte = self.byte.saturating_add_signed(delta.net_byte_delta());
+            return;
+        }
+
+        self.byte = match self.bias {
+            AnchorBias::Left => delta.range.start,
+            AnchorBias::Right => delta.range.start + delta.inserted.bytes,
+        };
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{Anchor, AnchorBias, EditDelta, RopeEdit, TextRange};
+    use crate::{TextMetrics, TextPoint};
+
+    #[test]
+    fn constructors_build_expected_edits() {
+        assert_eq!(RopeEdit::insert(2, "x").range, TextRange::new(2, 2));
+        assert_eq!(RopeEdit::delete(TextRange::new(2, 4)).insert, "");
+        assert_eq!(RopeEdit::replace(TextRange::new(1, 3), "zz").insert, "zz");
+    }
+
+    #[test]
+    fn text_range_helpers_report_size() {
+        let range = TextRange::new(3, 7);
+        assert_eq!(range.len(), 4);
+        assert!(!range.is_empty());
+        assert!(TextRange::new(5, 5).is_empty());
+    }
+
+    #[test]
+    fn anchors_map_before_inside_and_after_edits() {
+        let delta = EditDelta {
+            range: TextRange::new(4, 7),
+            removed_text: "abc".into(),
+            inserted_text: "x".into(),
+            removed: TextMetrics::from_text("abc"),
+            inserted: TextMetrics::from_text("x"),
+            start: TextPoint::origin().advance("1234"),
+            old_end: TextPoint::origin().advance("1234abc"),
+            new_end: TextPoint::origin().advance("1234x"),
+        };
+
+        let mut before = Anchor::new(2, AnchorBias::Left);
+        let mut inside_left = Anchor::new(5, AnchorBias::Left);
+        let mut inside_right = Anchor::new(5, AnchorBias::Right);
+        let mut after = Anchor::new(10, AnchorBias::Left);
+
+        before.map_through(&delta);
+        inside_left.map_through(&delta);
+        inside_right.map_through(&delta);
+        after.map_through(&delta);
+
+        assert_eq!(before.byte, 2);
+        assert_eq!(inside_left.byte, 4);
+        assert_eq!(inside_right.byte, 5);
+        assert_eq!(after.byte, 8);
+    }
+}

lib/reactivity_parsing/src/lib.rs

@@ -0,0 +1,24 @@
+//! Reactive rope text storage and incremental parsing substrate for RUIN.
+
+mod delta;
+mod metrics;
+mod parse;
+mod rope;
+mod tokentree;
+
+pub use delta::{Anchor, AnchorBias, EditDelta, RopeEdit, TextRange};
+pub use metrics::{TextMetrics, TextPoint};
+pub use parse::{
+    IncrementalParser, ParseError, ParseInvalidation, ParseResult, ParserCheckpoint, ParseTree,
+    SyntaxFragment,
+};
+pub use rope::{
+    DEFAULT_LEAF_TARGET_BYTES, ReactiveRope, RopeBuilder, RopeChunk, RopeCursor,
+    RopeSnapshotMetrics,
+};
+pub use tokentree::{
+    DelimiterKind, NumberBase, NumberLiteral, NumberSuffix, StringDelimiter, StringFragment,
+    ReactiveTokenTree, TokenTreeDiagnostic, TokenTreeDiagnosticKind, TokenTreeNode,
+    TokenTreeNodeKind, TokenTreeParse, TokenTreeParser, TokenTreeStats, TokenTreeUpdate,
+    TriviaComment, TriviaKind, TriviaStore,
+};

lib/reactivity_parsing/src/metrics.rs

@@ -0,0 +1,139 @@
+use core::fmt;
+
+#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
+pub struct TextMetrics {
+    pub bytes: usize,
+    pub chars: usize,
+    pub utf16: usize,
+    pub line_breaks: usize,
+}
+
+impl TextMetrics {
+    pub fn from_text(text: &str) -> Self {
+        let mut metrics = Self::default();
+        for ch in text.chars() {
+            metrics.bytes += ch.len_utf8();
+            metrics.chars += 1;
+            metrics.utf16 += ch.len_utf16();
+            metrics.line_breaks += usize::from(ch == '\n');
+        }
+        metrics
+    }
+}
+
+impl core::ops::Add for TextMetrics {
+    type Output = Self;
+
+    fn add(self, rhs: Self) -> Self::Output {
+        Self {
+            bytes: self.bytes + rhs.bytes,
+            chars: self.chars + rhs.chars,
+            utf16: self.utf16 + rhs.utf16,
+            line_breaks: self.line_breaks + rhs.line_breaks,
+        }
+    }
+}
+
+impl core::ops::AddAssign for TextMetrics {
+    fn add_assign(&mut self, rhs: Self) {
+        *self = *self + rhs;
+    }
+}
+
+impl core::ops::Sub for TextMetrics {
+    type Output = Self;
+
+    fn sub(self, rhs: Self) -> Self::Output {
+        Self {
+            bytes: self.bytes - rhs.bytes,
+            chars: self.chars - rhs.chars,
+            utf16: self.utf16 - rhs.utf16,
+            line_breaks: self.line_breaks - rhs.line_breaks,
+        }
+    }
+}
+
+#[derive(Clone, Copy, Default, Eq, PartialEq)]
+pub struct TextPoint {
+    pub byte: usize,
+    pub char_offset: usize,
+    pub utf16_offset: usize,
+    pub line: usize,
+    pub column: usize,
+}
+
+impl TextPoint {
+    pub const fn origin() -> Self {
+        Self {
+            byte: 0,
+            char_offset: 0,
+            utf16_offset: 0,
+            line: 0,
+            column: 0,
+        }
+    }
+
+    pub fn advance(mut self, text: &str) -> Self {
+        self.byte += text.len();
+        for ch in text.chars() {
+            self.char_offset += 1;
+            self.utf16_offset += ch.len_utf16();
+            if ch == '\n' {
+                self.line += 1;
+                self.column = 0;
+            } else {
+                self.column += 1;
+            }
+        }
+        self
+    }
+}
+
+impl fmt::Debug for TextPoint {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("TextPoint")
+            .field("byte", &self.byte)
+            .field("char_offset", &self.char_offset)
+            .field("utf16_offset", &self.utf16_offset)
+            .field("line", &self.line)
+            .field("column", &self.column)
+            .finish()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::{TextMetrics, TextPoint};
+
+    #[test]
+    fn metrics_count_utf8_utf16_and_lines() {
+        let metrics = TextMetrics::from_text("a\né🙂");
+        assert_eq!(metrics.bytes, "a\né🙂".len());
+        assert_eq!(metrics.chars, 4);
+        assert_eq!(metrics.utf16, 5);
+        assert_eq!(metrics.line_breaks, 1);
+    }
+
+    #[test]
+    fn metrics_support_arithmetic() {
+        let left = TextMetrics::from_text("hello\n");
+        let right = TextMetrics::from_text("🙂");
+        let combined = left + right;
+
+        assert_eq!(combined.bytes, "hello\n🙂".len());
+        assert_eq!(combined.chars, 7);
+        assert_eq!(combined.utf16, 8);
+        assert_eq!(combined.line_breaks, 1);
+        assert_eq!(combined - right, left);
+    }
+
+    #[test]
+    fn point_advance_tracks_offsets() {
+        let point = TextPoint::origin().advance("ab\n🙂");
+        assert_eq!(point.byte, "ab\n🙂".len());
+        assert_eq!(point.char_offset, 4);
+        assert_eq!(point.utf16_offset, 5);
+        assert_eq!(point.line, 1);
+        assert_eq!(point.column, 1);
+    }
+}

lib/reactivity_parsing/src/parse.rs

@@ -0,0 +1,162 @@
+use core::fmt;
+
+use crate::{RopeCursor, TextRange};
+
+pub trait ParserCheckpoint: Clone + Eq + fmt::Debug + 'static {}
+
+impl<T> ParserCheckpoint for T where T: Clone + Eq + fmt::Debug + 'static {}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct SyntaxFragment<C, T, D> {
+    pub range: TextRange,
+    pub start_checkpoint: C,
+    pub end_checkpoint: C,
+    pub tree: T,
+    pub diagnostics: Vec<D>,
+    pub grammar_revision: u64,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct ParseTree<T> {
+    pub root: T,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct ParseInvalidation<C> {
+    pub resume_at: usize,
+    pub restart_checkpoint: C,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct ParseResult<C, T, D> {
+    pub tree: ParseTree<T>,
+    pub fragments: Vec<SyntaxFragment<C, T, D>>,
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct ParseError {
+    pub message: String,
+}
+
+impl ParseError {
+    pub fn new(message: impl Into<String>) -> Self {
+        Self {
+            message: message.into(),
+        }
+    }
+}
+
+pub trait IncrementalParser {
+    type Checkpoint: ParserCheckpoint;
+    type Tree: Clone + fmt::Debug + 'static;
+    type Diagnostic: Clone + fmt::Debug + 'static;
+
+    fn grammar_revision(&self) -> u64;
+
+    fn initial_checkpoint(&self) -> Self::Checkpoint;
+
+    fn invalidate(
+        &self,
+        delta_range: TextRange,
+        previous_fragments: &[SyntaxFragment<Self::Checkpoint, Self::Tree, Self::Diagnostic>],
+    ) -> ParseInvalidation<Self::Checkpoint>;
+
+    fn parse(
+        &self,
+        cursor: RopeCursor,
+        fragments: &[SyntaxFragment<Self::Checkpoint, Self::Tree, Self::Diagnostic>],
+        invalidation: ParseInvalidation<Self::Checkpoint>,
+    ) -> Result<ParseResult<Self::Checkpoint, Self::Tree, Self::Diagnostic>, ParseError>;
+}
+
+#[cfg(test)]
+mod tests {
+    use std::cell::Cell;
+    use std::rc::Rc;
+
+    use ruin_reactivity::Reactor;
+
+    use super::{
+        IncrementalParser, ParseError, ParseInvalidation, ParseResult, ParseTree, SyntaxFragment,
+    };
+    use crate::{ReactiveRope, RopeCursor, TextRange};
+
+    #[derive(Clone, Debug)]
+    struct DummyParser {
+        parse_calls: Rc<Cell<usize>>,
+    }
+
+    impl IncrementalParser for DummyParser {
+        type Checkpoint = u8;
+        type Tree = String;
+        type Diagnostic = String;
+
+        fn grammar_revision(&self) -> u64 {
+            7
+        }
+
+        fn initial_checkpoint(&self) -> Self::Checkpoint {
+            0
+        }
+
+        fn invalidate(
+            &self,
+            delta_range: TextRange,
+            _previous_fragments: &[SyntaxFragment<Self::Checkpoint, Self::Tree, Self::Diagnostic>],
+        ) -> ParseInvalidation<Self::Checkpoint> {
+            ParseInvalidation {
+                resume_at: delta_range.start.saturating_sub(1),
+                restart_checkpoint: 1,
+            }
+        }
+
+        fn parse(
+            &self,
+            mut cursor: RopeCursor,
+            _fragments: &[SyntaxFragment<Self::Checkpoint, Self::Tree, Self::Diagnostic>],
+            invalidation: ParseInvalidation<Self::Checkpoint>,
+        ) -> 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()),
+                    start_checkpoint: invalidation.restart_checkpoint,
+                    end_checkpoint: 2,
+                    tree: text,
+                    diagnostics: Vec::new(),
+                    grammar_revision: self.grammar_revision(),
+                }],
+            })
+        }
+    }
+
+    #[test]
+    fn parse_error_constructor_sets_message() {
+        let error = ParseError::new("bad");
+        assert_eq!(error.message, "bad");
+    }
+
+    #[test]
+    fn parser_trait_round_trip_produces_fragments() {
+        let reactor = Reactor::new();
+        let rope = ReactiveRope::from_text(&reactor, "{\"a\":1}");
+        let parser = DummyParser {
+            parse_calls: Rc::new(Cell::new(0)),
+        };
+
+        let invalidation = parser.invalidate(TextRange::new(3, 4), &[]);
+        assert_eq!(invalidation.resume_at, 2);
+        assert_eq!(invalidation.restart_checkpoint, 1);
+
+        let result = parser
+            .parse(rope.cursor(0), &[], invalidation)
+            .expect("dummy parse should succeed");
+
+        assert_eq!(result.tree.root, "{\"a\":1}");
+        assert_eq!(result.fragments.len(), 1);
+        assert_eq!(result.fragments[0].grammar_revision, 7);
+        assert_eq!(parser.parse_calls.get(), 1);
+    }
+}

lib/reactivity_parsing/src/rope.rs

@@ -0,0 +1,720 @@
+use std::cell::{Cell, RefCell};
+use std::cmp::min;
+use std::collections::BTreeSet;
+use std::rc::Rc;
+
+use ruin_reactivity::{Event, Reactor, Source, event_in, source_in};
+
+use crate::delta::{EditDelta, RopeEdit, TextRange};
+use crate::metrics::{TextMetrics, TextPoint};
+
+pub const DEFAULT_LEAF_TARGET_BYTES: usize = 1024;
+const DEFAULT_LEAF_MAX_BYTES: usize = DEFAULT_LEAF_TARGET_BYTES * 2;
+
+#[derive(Clone)]
+pub struct ReactiveRope {
+    inner: Rc<RopeInner>,
+}
+
+pub struct RopeBuilder {
+    reactor: Reactor,
+    leaf_target_bytes: usize,
+    chunks: Vec<String>,
+}
+
+#[derive(Clone)]
+pub struct RopeChunk {
+    text: Rc<str>,
+    pub start: TextPoint,
+    pub metrics: TextMetrics,
+}
+
+#[derive(Clone)]
+pub struct RopeCursor {
+    rope: ReactiveRope,
+    next_offset: usize,
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub struct RopeSnapshotMetrics {
+    pub leaves: usize,
+    pub text: TextMetrics,
+    pub revision: u64,
+}
+
+struct RopeInner {
+    reactor: Reactor,
+    structure: Source,
+    revision: Cell<u64>,
+    leaf_target_bytes: usize,
+    leaves: RefCell<Vec<Rc<Leaf>>>,
+    edit_events: Event<EditDelta>,
+}
+
+struct Leaf {
+    source: Source,
+    text: RefCell<Rc<str>>,
+    metrics: Cell<TextMetrics>,
+    tail_chars: Cell<usize>,
+}
+
+impl RopeBuilder {
+    pub fn new(reactor: &Reactor) -> Self {
+        Self {
+            reactor: reactor.clone(),
+            leaf_target_bytes: DEFAULT_LEAF_TARGET_BYTES,
+            chunks: Vec::new(),
+        }
+    }
+
+    pub fn leaf_target_bytes(mut self, bytes: usize) -> Self {
+        self.leaf_target_bytes = bytes.max(32);
+        self
+    }
+
+    pub fn push(mut self, text: impl Into<String>) -> Self {
+        self.chunks.push(text.into());
+        self
+    }
+
+    pub fn build(self) -> ReactiveRope {
+        ReactiveRope::from_chunks(self.reactor, self.leaf_target_bytes, self.chunks)
+    }
+}
+
+impl ReactiveRope {
+    pub fn new(reactor: &Reactor) -> Self {
+        RopeBuilder::new(reactor).build()
+    }
+
+    pub fn from_text(reactor: &Reactor, text: impl AsRef<str>) -> Self {
+        RopeBuilder::new(reactor).push(text.as_ref()).build()
+    }
+
+    fn from_chunks(reactor: Reactor, leaf_target_bytes: usize, chunks: Vec<String>) -> Self {
+        let structure = source_in(&reactor);
+        let edit_events = event_in(&reactor);
+        let mut leaves = Vec::new();
+        for chunk in chunks {
+            Self::append_chunk_into(&reactor, leaf_target_bytes, &mut leaves, &chunk);
+        }
+        if leaves.is_empty() {
+            leaves.push(Rc::new(Leaf::new(&reactor, String::new())));
+        }
+
+        Self {
+            inner: Rc::new(RopeInner {
+                reactor,
+                structure,
+                revision: Cell::new(0),
+                leaf_target_bytes,
+                leaves: RefCell::new(leaves),
+                edit_events,
+            }),
+        }
+    }
+
+    pub fn edit_events(&self) -> Event<EditDelta> {
+        self.inner.edit_events.clone()
+    }
+
+    pub fn reactor(&self) -> Reactor {
+        self.inner.reactor.clone()
+    }
+
+    pub fn snapshot_metrics(&self) -> RopeSnapshotMetrics {
+        self.inner.structure.observe();
+        RopeSnapshotMetrics {
+            leaves: self.inner.leaves.borrow().len(),
+            text: self.total_metrics(),
+            revision: self.inner.revision.get(),
+        }
+    }
+
+    pub fn len_bytes(&self) -> usize {
+        self.total_metrics().bytes
+    }
+
+    pub fn is_empty(&self) -> bool {
+        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());
+        let mut point = TextPoint::origin();
+        let leaves = self.inner.leaves.borrow();
+        let mut remaining = offset;
+        for leaf in &*leaves {
+            let bytes = leaf.metrics.get().bytes;
+            if remaining > bytes {
+                remaining -= bytes;
+                point.byte += bytes;
+                point.char_offset += leaf.metrics.get().chars;
+                point.utf16_offset += leaf.metrics.get().utf16;
+                point.line += leaf.metrics.get().line_breaks;
+                if leaf.metrics.get().line_breaks == 0 {
+                    point.column += leaf.tail_chars.get();
+                } else {
+                    point.column = leaf.tail_chars.get();
+                }
+                continue;
+            }
+            let text = leaf.read();
+            point = point.advance(&text[..remaining]);
+            return point;
+        }
+        point
+    }
+
+    pub fn slice(&self, range: TextRange) -> String {
+        self.inner.structure.observe();
+        self.assert_char_boundary(range.start);
+        self.assert_char_boundary(range.end);
+        assert!(range.start <= range.end, "invalid text range");
+        assert!(range.end <= self.len_bytes(), "range out of bounds");
+
+        let mut out = String::with_capacity(range.len());
+        let mut cursor = 0usize;
+        let leaves = self.inner.leaves.borrow();
+        for leaf in &*leaves {
+            let metrics = leaf.metrics.get();
+            let end = cursor + metrics.bytes;
+            if end <= range.start {
+                cursor = end;
+                continue;
+            }
+            if cursor >= range.end {
+                break;
+            }
+            let text = leaf.read();
+            let start_in_leaf = range.start.saturating_sub(cursor);
+            let end_in_leaf = min(metrics.bytes, range.end - cursor);
+            out.push_str(&text[start_in_leaf..end_in_leaf]);
+            cursor = end;
+        }
+        out
+    }
+
+    pub fn chunk_at(&self, offset: usize) -> Option<RopeChunk> {
+        self.inner.structure.observe();
+        if offset >= self.len_bytes() {
+            return None;
+        }
+        let mut start = TextPoint::origin();
+        let leaves = self.inner.leaves.borrow();
+        let mut cursor = 0usize;
+        for leaf in &*leaves {
+            let metrics = leaf.metrics.get();
+            let end = cursor + metrics.bytes;
+            if offset < end {
+                let text = leaf.read();
+                leaf.source.observe();
+                return Some(RopeChunk {
+                    text,
+                    start,
+                    metrics,
+                });
+            }
+            start.byte += metrics.bytes;
+            start.char_offset += metrics.chars;
+            start.utf16_offset += metrics.utf16;
+            start.line += metrics.line_breaks;
+            if metrics.line_breaks == 0 {
+                start.column += leaf.tail_chars.get();
+            } else {
+                start.column = leaf.tail_chars.get();
+            }
+            cursor = end;
+        }
+        None
+    }
+
+    pub fn cursor(&self, offset: usize) -> RopeCursor {
+        RopeCursor {
+            rope: self.clone(),
+            next_offset: offset.min(self.len_bytes()),
+        }
+    }
+
+    pub fn edit(&self, edit: RopeEdit) -> EditDelta {
+        let delta = self.apply_edit(edit);
+        self.inner.edit_events.emit(delta.clone());
+        delta
+    }
+
+    pub fn edit_batch(&self, edits: impl IntoIterator<Item = RopeEdit>) -> Vec<EditDelta> {
+        let mut deltas = Vec::new();
+        for edit in edits {
+            let delta = self.apply_edit(edit);
+            self.inner.edit_events.emit(delta.clone());
+            deltas.push(delta);
+        }
+        deltas
+    }
+
+    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");
+        self.assert_char_boundary(edit.range.start);
+        self.assert_char_boundary(edit.range.end);
+        assert!(
+            edit.insert.is_char_boundary(edit.insert.len()),
+            "replacement text must be valid UTF-8"
+        );
+
+        let old_start = self.point_at(edit.range.start);
+        let old_end = self.point_at(edit.range.end);
+        let removed_text = self.slice(edit.range);
+        let removed = TextMetrics::from_text(&removed_text);
+        let inserted = TextMetrics::from_text(&edit.insert);
+
+        let mut leaves = self.inner.leaves.borrow_mut();
+        let mut cursor = 0usize;
+        let mut first_index = None;
+        let mut last_index = None;
+        let mut prefix = String::new();
+        let mut suffix = String::new();
+
+        for (index, leaf) in leaves.iter().enumerate() {
+            let text = leaf.read();
+            let end = cursor + text.len();
+            if first_index.is_none() && edit.range.start <= end {
+                first_index = Some(index);
+                let split = edit.range.start.saturating_sub(cursor);
+                prefix.push_str(&text[..split]);
+            }
+            if first_index.is_some() && edit.range.end <= end {
+                last_index = Some(index);
+                let split = edit.range.end.saturating_sub(cursor);
+                suffix.push_str(&text[split..]);
+                break;
+            }
+            cursor = end;
+        }
+
+        let first_index = first_index.unwrap_or_else(|| leaves.len().saturating_sub(1));
+        let last_index = last_index.unwrap_or(first_index);
+
+        let mut replacement = prefix;
+        replacement.push_str(&edit.insert);
+        replacement.push_str(&suffix);
+
+        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);
+                leaf.source.trigger();
+            }
+        } else {
+            let mut replacement_leaves = Vec::new();
+            Self::append_chunk_into(
+                &self.inner.reactor,
+                self.inner.leaf_target_bytes,
+                &mut replacement_leaves,
+                &replacement,
+            );
+            if replacement_leaves.is_empty() {
+                replacement_leaves.push(Rc::new(Leaf::new(&self.inner.reactor, String::new())));
+            }
+
+            let removed_span = leaves.splice(first_index..=last_index, replacement_leaves);
+            let mut touched = BTreeSet::new();
+            for leaf in removed_span {
+                touched.insert(leaf.source.id());
+            }
+            for leaf in leaves.iter().skip(first_index) {
+                touched.insert(leaf.source.id());
+            }
+            for leaf in &*leaves {
+                if touched.contains(&leaf.source.id()) {
+                    leaf.source.trigger();
+                }
+            }
+            self.inner.structure.trigger();
+        }
+
+        self.inner.revision.set(self.inner.revision.get().wrapping_add(1));
+
+        let new_end = old_start.advance(&edit.insert);
+        drop(leaves);
+
+        EditDelta {
+            range: edit.range,
+            removed_text,
+            inserted_text: edit.insert,
+            removed,
+            inserted,
+            start: old_start,
+            old_end,
+            new_end,
+        }
+    }
+
+    fn total_metrics(&self) -> TextMetrics {
+        self.inner
+            .leaves
+            .borrow()
+            .iter()
+            .fold(TextMetrics::default(), |sum, leaf| sum + leaf.metrics.get())
+    }
+
+    fn append_chunk_into(
+        reactor: &Reactor,
+        leaf_target_bytes: usize,
+        out: &mut Vec<Rc<Leaf>>,
+        text: &str,
+    ) {
+        if text.is_empty() {
+            return;
+        }
+
+        let max_bytes = (leaf_target_bytes.max(32)) * 2;
+        let mut start = 0usize;
+        while start < text.len() {
+            let mut end = min(text.len(), start + max_bytes);
+            while end > start && !text.is_char_boundary(end) {
+                end -= 1;
+            }
+            if end == start {
+                end = text.len();
+            }
+            out.push(Rc::new(Leaf::new(reactor, text[start..end].to_string())));
+            start = end;
+        }
+    }
+
+    fn assert_char_boundary(&self, offset: usize) {
+        if offset == self.len_bytes() {
+            return;
+        }
+        let leaves = self.inner.leaves.borrow();
+        let mut cursor = 0usize;
+        for leaf in &*leaves {
+            let bytes = leaf.metrics.get().bytes;
+            let end = cursor + bytes;
+            if offset < end {
+                let text = leaf.read();
+                assert!(text.is_char_boundary(offset - cursor), "offset must be a char boundary");
+                return;
+            }
+            cursor = end;
+        }
+    }
+}
+
+impl RopeChunk {
+    pub fn text(&self) -> &str {
+        &self.text
+    }
+}
+
+impl RopeCursor {
+    pub fn offset(&self) -> usize {
+        self.next_offset
+    }
+
+    pub fn peek_chunk(&self) -> Option<RopeChunk> {
+        let chunk = self.rope.chunk_at(self.next_offset)?;
+        let local = self.next_offset.saturating_sub(chunk.start.byte);
+        if local == 0 {
+            return Some(chunk);
+        }
+
+        let partial = &chunk.text()[local..];
+        Some(RopeChunk {
+            text: Rc::from(partial),
+            start: self.rope.point_at(self.next_offset),
+            metrics: TextMetrics::from_text(partial),
+        })
+    }
+
+    pub fn next_chunk(&mut self) -> Option<RopeChunk> {
+        let chunk = self.peek_chunk()?;
+        let end = chunk.start.byte + chunk.metrics.bytes;
+        self.next_offset = end;
+        Some(chunk)
+    }
+
+    pub fn read_bytes(&mut self, len: usize) -> String {
+        let start = self.next_offset;
+        let end = min(self.rope.len_bytes(), start + len);
+        let slice = self.rope.slice(TextRange::new(start, end));
+        self.next_offset = end;
+        slice
+    }
+}
+
+impl Leaf {
+    fn new(reactor: &Reactor, text: String) -> Self {
+        let text: Rc<str> = Rc::from(text);
+        let metrics = TextMetrics::from_text(&text);
+        let tail_chars = tail_chars(&text);
+        Self {
+            source: source_in(reactor),
+            text: RefCell::new(text),
+            metrics: Cell::new(metrics),
+            tail_chars: Cell::new(tail_chars),
+        }
+    }
+
+    fn read(&self) -> Rc<str> {
+        self.source.observe();
+        self.text.borrow().clone()
+    }
+
+    fn set_text(&self, text: String) {
+        let text: Rc<str> = Rc::from(text);
+        self.metrics.set(TextMetrics::from_text(&text));
+        self.tail_chars.set(tail_chars(&text));
+        *self.text.borrow_mut() = text;
+    }
+}
+
+fn tail_chars(text: &str) -> usize {
+    match text.rfind('\n') {
+        Some(index) => text[index + 1..].chars().count(),
+        None => text.chars().count(),
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use std::cell::Cell as Counter;
+    use std::cell::RefCell;
+    use std::panic::{AssertUnwindSafe, catch_unwind};
+    use std::rc::Rc;
+
+    use ruin_reactivity::{Reactor, thunk_in};
+
+    use crate::{Anchor, AnchorBias, ReactiveRope, RopeBuilder, RopeEdit, TextRange};
+
+    #[test]
+    fn edits_preserve_text_and_metrics() {
+        let reactor = Reactor::new();
+        let rope = ReactiveRope::from_text(&reactor, "hello\nworld");
+
+        let delta = rope.edit(RopeEdit::replace(TextRange::new(5, 6), ", "));
+
+        assert_eq!(rope.to_string(), "hello, world");
+        assert_eq!(delta.removed_text, "\n");
+        assert_eq!(delta.inserted_text, ", ");
+        assert_eq!(rope.snapshot_metrics().text.bytes, "hello, world".len());
+        assert_eq!(rope.snapshot_metrics().text.line_breaks, 0);
+    }
+
+    #[test]
+    fn cursor_walks_tokens_across_leaf_boundaries() {
+        let reactor = Reactor::new();
+        let rope = RopeBuilder::new(&reactor)
+            .leaf_target_bytes(4)
+            .push("alpha")
+            .push("beta")
+            .build();
+        let mut cursor = rope.cursor(3);
+
+        assert_eq!(cursor.read_bytes(4), "habe");
+        let rest = cursor.next_chunk().expect("remaining chunk");
+        assert_eq!(rest.text(), "ta");
+    }
+
+    #[test]
+    fn anchors_map_through_insertions() {
+        let reactor = Reactor::new();
+        let rope = ReactiveRope::from_text(&reactor, "abcdef");
+        let mut left = Anchor::new(3, AnchorBias::Left);
+        let mut right = Anchor::new(3, AnchorBias::Right);
+
+        let delta = rope.edit(RopeEdit::insert(3, "XYZ"));
+        left.map_through(&delta);
+        right.map_through(&delta);
+
+        assert_eq!(left.byte, 3);
+        assert_eq!(right.byte, 6);
+    }
+
+    #[test]
+    fn disjoint_leaf_reads_do_not_recompute_on_local_edit() {
+        let reactor = Reactor::new();
+        let rope = RopeBuilder::new(&reactor)
+            .leaf_target_bytes(64)
+            .push("a".repeat(80))
+            .push("b".repeat(80))
+            .build();
+
+        let first_runs = Rc::new(Counter::new(0usize));
+        let second_runs = Rc::new(Counter::new(0usize));
+
+        let first = thunk_in(&reactor, {
+            let rope = rope.clone();
+            let first_runs = Rc::clone(&first_runs);
+            move || {
+                first_runs.set(first_runs.get() + 1);
+                rope.slice(TextRange::new(0, 10))
+            }
+        });
+
+        let second = thunk_in(&reactor, {
+            let rope = rope.clone();
+            let second_runs = Rc::clone(&second_runs);
+            move || {
+                second_runs.set(second_runs.get() + 1);
+                rope.slice(TextRange::new(90, 100))
+            }
+        });
+
+        assert_eq!(first.get(), "aaaaaaaaaa");
+        assert_eq!(second.get(), "bbbbbbbbbb");
+        rope.edit(RopeEdit::replace(TextRange::new(2, 4), "zz"));
+
+        assert_eq!(first.get(), "aazzaaaaaa");
+        assert_eq!(second.get(), "bbbbbbbbbb");
+        assert_eq!(first_runs.get(), 2);
+        assert_eq!(second_runs.get(), 1);
+    }
+
+    #[test]
+    fn point_at_tracks_multibyte_offsets() {
+        let reactor = Reactor::new();
+        let rope = ReactiveRope::from_text(&reactor, "a\né🙂");
+
+        assert_eq!(rope.point_at(0).byte, 0);
+        assert_eq!(rope.point_at(2).line, 1);
+        assert_eq!(rope.point_at(4).char_offset, 3);
+        assert_eq!(rope.point_at("a\né🙂".len()).utf16_offset, 5);
+        assert_eq!(rope.point_at("a\né".len()).column, 1);
+    }
+
+    #[test]
+    fn point_at_tracks_column_across_leaves() {
+        let reactor = Reactor::new();
+        let rope = RopeBuilder::new(&reactor)
+            .leaf_target_bytes(4)
+            .push("ab\n")
+            .push("cde")
+            .build();
+
+        let point = rope.point_at("ab\ncd".len());
+        assert_eq!(point.line, 1);
+        assert_eq!(point.column, 2);
+    }
+
+    #[test]
+    fn chunk_at_and_peek_chunk_respect_boundaries() {
+        let reactor = Reactor::new();
+        let rope = RopeBuilder::new(&reactor)
+            .leaf_target_bytes(4)
+            .push("abcd")
+            .push("efgh")
+            .build();
+
+        let first = rope.chunk_at(0).expect("chunk at start");
+        assert_eq!(first.text(), "abcd");
+
+        let second = rope.chunk_at(4).expect("chunk at split");
+        assert_eq!(second.text(), "efgh");
+        assert!(rope.chunk_at(8).is_none());
+
+        let mut cursor = rope.cursor(2);
+        let partial = cursor.peek_chunk().expect("partial chunk");
+        assert_eq!(partial.text(), "cd");
+        let advanced = cursor.next_chunk().expect("advanced chunk");
+        assert_eq!(advanced.text(), "cd");
+        assert_eq!(cursor.offset(), 4);
+    }
+
+    #[test]
+    fn cursor_stops_at_end_of_document() {
+        let reactor = Reactor::new();
+        let rope = RopeBuilder::new(&reactor)
+            .leaf_target_bytes(4)
+            .push("abcd")
+            .push("ef")
+            .build();
+        let mut cursor = rope.cursor(0);
+        let mut chunks = Vec::new();
+        while let Some(chunk) = cursor.next_chunk() {
+            chunks.push(chunk.text().to_string());
+        }
+
+        assert_eq!(chunks, vec!["abcd".to_string(), "ef".to_string()]);
+        assert!(cursor.next_chunk().is_none());
+    }
+
+    #[test]
+    fn batch_edits_return_deltas_and_increment_revision() {
+        let reactor = Reactor::new();
+        let rope = ReactiveRope::from_text(&reactor, "abcdef");
+        let before = rope.snapshot_metrics().revision;
+
+        let deltas = rope.edit_batch([
+            RopeEdit::replace(TextRange::new(1, 3), "ZZ"),
+            RopeEdit::delete(TextRange::new(4, 6)),
+        ]);
+
+        assert_eq!(deltas.len(), 2);
+        assert_eq!(rope.to_string(), "aZZd");
+        assert_eq!(rope.snapshot_metrics().revision, before + 2);
+    }
+
+    #[test]
+    fn delete_to_empty_preserves_valid_empty_rope() {
+        let reactor = Reactor::new();
+        let rope = ReactiveRope::from_text(&reactor, "hello");
+
+        let delta = rope.edit(RopeEdit::delete(TextRange::new(0, 5)));
+
+        assert_eq!(delta.removed_text, "hello");
+        assert!(rope.is_empty());
+        assert_eq!(rope.to_string(), "");
+        assert_eq!(rope.snapshot_metrics().leaves, 1);
+    }
+
+    #[test]
+    fn structure_changing_edit_updates_leaf_count() {
+        let reactor = Reactor::new();
+        let rope = RopeBuilder::new(&reactor)
+            .leaf_target_bytes(8)
+            .push("abcdefgh")
+            .push("ijklmnop")
+            .build();
+        let before = rope.snapshot_metrics();
+
+        rope.edit(RopeEdit::insert(8, "QRSTUVWXYZ0123456789"));
+        let after = rope.snapshot_metrics();
+
+        assert!(after.leaves >= before.leaves);
+        assert!(after.text.bytes > before.text.bytes);
+    }
+
+    #[test]
+    fn invalid_char_boundary_panics() {
+        let reactor = Reactor::new();
+        let rope = ReactiveRope::from_text(&reactor, "é");
+
+        let panic = catch_unwind(AssertUnwindSafe(|| {
+            let _ = rope.slice(TextRange::new(1, 2));
+        }));
+
+        assert!(panic.is_err());
+    }
+
+    #[test]
+    fn edit_events_emit_immediately() {
+        let reactor = Reactor::new();
+        let rope = ReactiveRope::from_text(&reactor, "abc");
+        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()))
+        });
+
+        rope.edit(RopeEdit::insert(1, "Z"));
+
+        assert_eq!(&*seen.borrow(), &[(TextRange::new(1, 1), "Z".to_string())]);
+    }
+}

lib/ruin_app/example/00_bootstrap_and_counter.rs

@@ -1,4 +1,5 @@
-use ruin_app::prelude::*;
+use ruin_app::{PartialTextStyle, prelude::*};
+use ruin_ui::{BoxShadow, BoxShadowKind, Point};
 
 #[ruin_runtime::async_main]
 async fn main() -> ruin_app::Result<()> {
@@ -9,6 +10,8 @@ async fn main() -> ruin_app::Result<()> {
             Window::new()
                 .title(title)
                 .app_id("dev.ruin.counter")
+                .base_color(Color::rgba(255, 255, 255, 80))
+                .min_size(320.0, 240.0)
                 .size(960.0, 640.0),
         )
         .mount(view! {
@@ -31,9 +34,15 @@ fn CounterApp(title: &'static str) -> impl IntoView {
         move || format!("{title} ({})", count.get())
     });
 
+    let text_style = PartialTextStyle {
+        color: Some(Color::BLACK),
+        weight: Some(FontWeight::Bold),
+        ..Default::default()
+    };
+
     view! {
-        column(gap = 16.0, padding = 24.0) {
-            text(role = TextRole::Heading(1), size = 32.0, weight = FontWeight::Semibold) {
+        column(gap = 16.0, padding = 24.0, align_items = AlignItems::Center, text_style = text_style) {
+            text(role = TextRole::Heading(1), size = 32.0, weight = FontWeight::Semibold, color = Color::rgba(0, 0, 0, 255)) {
                 title
             }
 
@@ -42,12 +51,14 @@ fn CounterApp(title: &'static str) -> impl IntoView {
             block(
                 padding = 16.0,
                 gap = 8.0,
-                background = surfaces::raised(),
+                align_self = AlignItems::Stretch,
+                background = Color::rgba(255, 255, 255, 200),
                 border_radius = 12.0,
-                border = Border::new(2.0, Color::rgb(0, 0, 0))
+                border = Border::new(2.0, Color::rgba(0, 0, 0, 120)),
+                shadow = BoxShadow::new(Point::new(2.0, 2.0), 8.0, 2.0, Color::rgba(0, 0, 0, 60), BoxShadowKind::Outer),
             ) {
-                text(size = 18.0) { "count = "; count.clone() }
-                text(color = colors::muted()) { "double = "; doubled.clone() }
+                text(size = 18.0, color = Color::rgb(0, 0, 0)) { "count = "; count.clone() }
+                text(color = Color::rgba(0, 0, 0, 200)) { "double = "; doubled.clone() }
             }
         }
     }
@@ -56,8 +67,9 @@ fn CounterApp(title: &'static str) -> impl IntoView {
 #[component]
 fn CounterActions(count: Signal<i32>) -> impl IntoView {
     view! {
-        row(gap = 8.0) {
+        row(gap = 16.0) {
             button(
+                background = Color::rgba(255, 255, 255, 90),
                 on_press = {
                     let count = count.clone();
                     move |_| {
@@ -65,10 +77,11 @@ fn CounterActions(count: Signal<i32>) -> impl IntoView {
                     }
                 },
             ) {
-                "-1"
+                text(selectable = false, pointer_events = false) { "-1" }
             }
 
             button(
+                background = Color::rgba(255, 255, 255, 90),
                 on_press = {
                     let count = count.clone();
                     move |_| {
@@ -76,10 +89,11 @@ fn CounterActions(count: Signal<i32>) -> impl IntoView {
                     }
                 },
             ) {
-                "Reset"
+                text(selectable = false, pointer_events = false) { "Reset" }
             }
 
             button(
+                background = Color::rgba(255, 255, 255, 90),
                 on_press = {
                     let count = count.clone();
                     move |_| {
@@ -87,7 +101,7 @@ fn CounterActions(count: Signal<i32>) -> impl IntoView {
                     }
                 },
             ) {
-                "+1"
+                text(selectable = false, pointer_events = false) { "+1" }
             }
         }
     }

lib/ruin_app/example/03_fine_grained_list.rs

@@ -4,8 +4,7 @@ use tracing_subscriber::util::SubscriberInitExt;
 use tracing_subscriber::{EnvFilter, fmt};
 
 fn install_tracing() {
-    let filter = EnvFilter::try_from_default_env()
-        .unwrap_or_else(|_| EnvFilter::new("warn"));
+    let filter = EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new("warn"));
     let fmt_layer = fmt::layer()
         .with_target(true)
         .with_thread_ids(true)

lib/ruin_app/src/app.rs

@@ -0,0 +1,540 @@
+use std::cell::Cell as StdCell;
+use std::cell::RefCell;
+use std::iter;
+use std::rc::Rc;
+use std::time::Instant;
+
+use ruin_reactivity::effect;
+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,
+};
+use ruin_ui_platform_wayland::start_wayland_ui;
+
+use crate::Result;
+use crate::context::{
+    InteractionSnapshot, RenderState, render_with_context, render_with_context_and_interaction,
+};
+use crate::input::{
+    EventBindings, InputState, ShortcutBinding, TextSelection, TextSelectionDrag,
+    TextSelectionState, apply_text_selection_overlay, focused_element_for_pointer,
+    sync_primary_selection,
+};
+use crate::view::View;
+
+#[derive(Clone, Debug)]
+pub struct Window {
+    pub(crate) spec: WindowSpec,
+}
+
+impl Window {
+    pub fn new() -> Self {
+        Self {
+            spec: WindowSpec::new("RUIN App"),
+        }
+    }
+
+    pub fn title(mut self, title: impl Into<String>) -> Self {
+        self.spec.title = title.into();
+        self
+    }
+
+    pub fn app_id(mut self, app_id: impl Into<String>) -> Self {
+        self.spec = self.spec.app_id(app_id);
+        self
+    }
+
+    pub fn size(mut self, width: f32, height: f32) -> Self {
+        self.spec = self.spec.requested_inner_size(UiSize::new(width, height));
+        self
+    }
+
+    pub fn min_size(mut self, min_width: f32, min_height: f32) -> Self {
+        self.spec = self.spec.min_inner_size(UiSize::new(min_width, min_height));
+        self
+    }
+
+    pub fn base_color(mut self, color: Color) -> Self {
+        self.spec = self.spec.base_color(color);
+        self
+    }
+
+    pub fn resizable(mut self, resizable: bool) -> Self {
+        self.spec.resizable = resizable;
+        self
+    }
+}
+
+impl Default for Window {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+pub struct App {
+    window: Window,
+}
+
+impl App {
+    pub fn new() -> Self {
+        Self {
+            window: Window::new(),
+        }
+    }
+
+    pub fn window(mut self, window: Window) -> Self {
+        self.window = window;
+        self
+    }
+
+    pub fn mount<M: Mountable>(self, root: M) -> MountedApp<M> {
+        MountedApp {
+            window: self.window,
+            root: Rc::new(root),
+            render_state: Rc::new(RenderState::default()),
+        }
+    }
+}
+
+impl Default for App {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+pub trait Mountable: 'static {
+    fn render(&self) -> View;
+}
+
+pub trait Component: 'static {
+    type Builder;
+
+    fn builder() -> Self::Builder;
+    fn render(&self) -> View;
+}
+
+pub trait ContextKey: 'static {
+    type Value: Clone + 'static;
+}
+
+impl<T: Component> Mountable for T {
+    fn render(&self) -> View {
+        Component::render(self)
+    }
+}
+
+impl Mountable for View {
+    fn render(&self) -> View {
+        self.clone()
+    }
+}
+
+impl Mountable for Element {
+    fn render(&self) -> View {
+        View::from_element(self.clone())
+    }
+}
+
+pub struct MountedApp<M: Mountable> {
+    pub(crate) window: Window,
+    pub(crate) root: Rc<M>,
+    pub(crate) render_state: Rc<RenderState>,
+}
+
+impl<M: Mountable> MountedApp<M> {
+    pub async fn run(self) -> Result<()> {
+        let MountedApp {
+            window: app_window,
+            root,
+            render_state,
+        } = self;
+
+        let mut ui = start_wayland_ui();
+        let window = ui.create_window(app_window.spec.clone())?;
+        let initial_viewport = app_window
+            .spec
+            .requested_inner_size
+            .unwrap_or(UiSize::new(960.0, 640.0));
+
+        let viewport = ruin_reactivity::cell(initial_viewport);
+        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()));
+        let interaction_tree = Rc::new(RefCell::new(None::<InteractionTree>));
+        let bindings = Rc::new(RefCell::new(EventBindings::default()));
+        let shortcuts = Rc::new(RefCell::new(Vec::<ShortcutBinding>::new()));
+        let current_title = Rc::new(RefCell::new(None::<String>));
+        let last_min_size = Rc::new(RefCell::new(None::<UiSize>));
+        let last_fixed_size = Rc::new(RefCell::new(None::<UiSize>));
+        let explicit_min_size = app_window.spec.min_inner_size;
+        let explicit_max_size = app_window.spec.max_inner_size;
+        let window_resizable = app_window.spec.resizable;
+        let mut input_state = InputState::new();
+        let mut pointer_router = PointerRouter::new();
+
+        let _scene_effect = effect({
+            let window = window.clone();
+            let viewport = viewport.clone();
+            let text_system = Rc::clone(&text_system);
+            let layout_cache = Rc::clone(&layout_cache);
+            let interaction_tree = Rc::clone(&interaction_tree);
+            let bindings = Rc::clone(&bindings);
+            let shortcuts = Rc::clone(&shortcuts);
+            let current_title = Rc::clone(&current_title);
+            let last_min_size = Rc::clone(&last_min_size);
+            let last_fixed_size = Rc::clone(&last_fixed_size);
+            let root = Rc::clone(&root);
+            let render_state = Rc::clone(&render_state);
+            let text_selection = Rc::clone(&input_state.text_selection);
+            let hovered_elements = input_state.hovered_elements.clone();
+            let pressed_elements = input_state.pressed_elements.clone();
+            let interaction_version = input_state.interaction_version.clone();
+            move || {
+                let viewport = viewport.get();
+                let version = scene_version.get().wrapping_add(1);
+                scene_version.set(version);
+                let _ = text_selection.version.get();
+                let _ = interaction_version.get();
+
+                let t_effect = Instant::now();
+                let interaction_snapshot = Rc::new(InteractionSnapshot {
+                    hovered: hovered_elements.get(),
+                    pressed: pressed_elements.get(),
+                });
+
+                let render_output = render_with_context_and_interaction(
+                    Rc::clone(&render_state),
+                    interaction_snapshot,
+                    || root.render(),
+                );
+
+                if render_output.side_effects.window_title != *current_title.borrow() {
+                    if let Some(title) = &render_output.side_effects.window_title {
+                        window
+                            .update(WindowUpdate::new().title(title.clone()))
+                            .expect("window should remain alive while the app is running");
+                    }
+                    *current_title.borrow_mut() = render_output.side_effects.window_title.clone();
+                }
+
+                let render_us = t_effect.elapsed().as_micros();
+                let t_layout = Instant::now();
+                let LayoutSnapshot {
+                    mut scene,
+                    interaction_tree: next_interaction_tree,
+                    root_min_size,
+                } = layout_snapshot_with_cache(
+                    version,
+                    viewport,
+                    render_output.view.element(),
+                    &mut text_system.borrow_mut(),
+                    &mut layout_cache.borrow_mut(),
+                );
+                let layout_us = t_layout.elapsed().as_micros();
+
+                let desired_min = UiSize::new(
+                    root_min_size
+                        .width
+                        .max(explicit_min_size.map_or(0.0, |s| s.width)),
+                    root_min_size
+                        .height
+                        .max(explicit_min_size.map_or(0.0, |s| s.height)),
+                );
+                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)));
+                        *last_min_size.borrow_mut() = Some(desired_min);
+                    }
+                } else {
+                    let desired_fixed = UiSize::new(
+                        desired_min
+                            .width
+                            .min(explicit_max_size.map_or(f32::INFINITY, |s| s.width)),
+                        desired_min
+                            .height
+                            .min(explicit_max_size.map_or(f32::INFINITY, |s| s.height)),
+                    );
+                    let current_fixed = *last_fixed_size.borrow();
+                    if current_fixed != Some(desired_fixed) {
+                        let _ = window.update(
+                            WindowUpdate::new()
+                                .requested_inner_size(Some(desired_fixed))
+                                .min_inner_size(Some(desired_fixed))
+                                .max_inner_size(Some(desired_fixed)),
+                        );
+                        *last_fixed_size.borrow_mut() = Some(desired_fixed);
+                    }
+                }
+                let effect_us = t_effect.elapsed().as_micros();
+
+                tracing::debug!(
+                    target: "ruin_app::resize",
+                    version,
+                    width = viewport.width,
+                    height = viewport.height,
+                    render_us,
+                    layout_us,
+                    effect_us,
+                    "scene effect complete, sending ReplaceScene"
+                );
+
+                apply_text_selection_overlay(&mut scene, *text_selection.selection.borrow());
+
+                *interaction_tree.borrow_mut() = Some(next_interaction_tree);
+                *bindings.borrow_mut() = render_output.view.bindings;
+                *shortcuts.borrow_mut() = render_output.side_effects.shortcuts.clone();
+                window
+                    .replace_scene(scene)
+                    .expect("window should remain alive while the app is running");
+            }
+        });
+
+        loop {
+            let Some(event) = ui.next_event().await else {
+                break;
+            };
+
+            for event in iter::once(event).chain(ui.take_pending_events()) {
+                match event {
+                    PlatformEvent::Configured {
+                        window_id,
+                        configuration,
+                    } if window_id == window.id() => {
+                        tracing::debug!(
+                            target: "ruin_app::resize",
+                            width = configuration.actual_inner_size.width,
+                            height = configuration.actual_inner_size.height,
+                            "app received Configured, queuing layout effect"
+                        );
+                        let _ = viewport.set(configuration.actual_inner_size);
+                    }
+                    PlatformEvent::Pointer { window_id, event } if window_id == window.id() => {
+                        Self::handle_pointer_event(
+                            &window,
+                            &interaction_tree,
+                            &bindings,
+                            &mut pointer_router,
+                            &mut input_state,
+                            event,
+                        )?;
+                    }
+                    PlatformEvent::Keyboard { window_id, event } if window_id == window.id() => {
+                        Self::handle_keyboard_event(
+                            &interaction_tree,
+                            &bindings,
+                            &shortcuts,
+                            &input_state,
+                            event,
+                        )?;
+                    }
+                    PlatformEvent::CloseRequested { window_id } if window_id == window.id() => {
+                        let _ = window.update(WindowUpdate::new().open(false));
+                    }
+                    PlatformEvent::Closed { window_id } if window_id == window.id() => {
+                        ui.shutdown()?;
+                        return Ok(());
+                    }
+                    _ => {}
+                }
+            }
+        }
+
+        ui.shutdown()?;
+        Ok(())
+    }
+
+    pub(crate) fn handle_pointer_event(
+        window: &WindowController,
+        interaction_tree: &RefCell<Option<InteractionTree>>,
+        bindings: &RefCell<EventBindings>,
+        pointer_router: &mut PointerRouter,
+        input_state: &mut InputState,
+        event: PointerEvent,
+    ) -> Result<()> {
+        if matches!(
+            event.kind,
+            PointerEventKind::Down {
+                button: PointerButton::Primary | PointerButton::Middle,
+            }
+        ) {
+            let interaction_tree = interaction_tree.borrow();
+            if let Some(interaction_tree) = interaction_tree.as_ref() {
+                input_state.focused_element = focused_element_for_pointer(interaction_tree, &event);
+            }
+        }
+
+        let routed = {
+            let interaction_tree = interaction_tree.borrow();
+            let Some(interaction_tree) = interaction_tree.as_ref() else {
+                return Ok(());
+            };
+            pointer_router.route(interaction_tree, event)
+        };
+
+        {
+            let interaction_tree = interaction_tree.borrow();
+            let Some(interaction_tree) = interaction_tree.as_ref() else {
+                return Ok(());
+            };
+            let hovered_targets = pointer_router.hovered_targets();
+            for routed_event in &routed {
+                bindings
+                    .borrow()
+                    .dispatch(routed_event, interaction_tree, hovered_targets);
+                Self::handle_text_selection_event(
+                    window,
+                    interaction_tree,
+                    routed_event,
+                    &input_state.text_selection,
+                )?;
+            }
+        }
+
+        let next_cursor = pointer_router
+            .hovered_targets()
+            .last()
+            .map(|target| target.cursor)
+            .unwrap_or(ruin_ui::CursorIcon::Default);
+        let hovered_ids = Self::interaction_ids(pointer_router.hovered_targets());
+        let pressed_ids = Self::interaction_ids(pointer_router.pressed_targets());
+        if next_cursor != input_state.current_cursor {
+            input_state.current_cursor = next_cursor;
+            window.set_cursor_icon(next_cursor)?;
+        }
+        if Self::update_interaction_state(input_state, hovered_ids, pressed_ids) {
+            input_state.interaction_version.update(|value| *value += 1);
+        }
+
+        Ok(())
+    }
+
+    pub(crate) fn handle_keyboard_event(
+        interaction_tree: &RefCell<Option<InteractionTree>>,
+        bindings: &RefCell<EventBindings>,
+        shortcuts: &RefCell<Vec<ShortcutBinding>>,
+        input_state: &InputState,
+        event: KeyboardEvent,
+    ) -> Result<()> {
+        let interaction_tree = interaction_tree.borrow();
+        let Some(interaction_tree) = interaction_tree.as_ref() else {
+            return Ok(());
+        };
+        let shortcut_bindings = shortcuts.borrow().clone();
+        let mut consumed = false;
+        for shortcut in shortcut_bindings {
+            if shortcut.matches(&event, input_state.focused_element, interaction_tree) {
+                shortcut.trigger(interaction_tree);
+                consumed = true;
+            }
+        }
+        if consumed {
+            return Ok(());
+        }
+        bindings
+            .borrow()
+            .dispatch_key(input_state.focused_element, &event, interaction_tree);
+        Ok(())
+    }
+
+    fn handle_text_selection_event(
+        window: &WindowController,
+        interaction_tree: &InteractionTree,
+        event: &RoutedPointerEvent,
+        text_selection: &TextSelectionState,
+    ) -> Result<()> {
+        let mut selection_changed = false;
+
+        match event.kind {
+            RoutedPointerEventKind::Down {
+                button: PointerButton::Primary,
+            } => {
+                if let Some(hit) = interaction_tree.text_hit_test(event.position)
+                    && let Some(element_id) = hit.target.element_id
+                {
+                    let next = Some(TextSelection {
+                        element_id,
+                        anchor: hit.byte_offset,
+                        focus: hit.byte_offset,
+                    });
+                    if *text_selection.selection.borrow() != next {
+                        *text_selection.selection.borrow_mut() = next;
+                        selection_changed = true;
+                    }
+                    *text_selection.drag.borrow_mut() = Some(TextSelectionDrag {
+                        element_id,
+                        anchor: hit.byte_offset,
+                    });
+                } else {
+                    selection_changed = text_selection.selection.borrow_mut().take().is_some();
+                    let _ = text_selection.drag.borrow_mut().take();
+                }
+            }
+            RoutedPointerEventKind::Move => {
+                let Some(drag) = *text_selection.drag.borrow() else {
+                    return Ok(());
+                };
+                let Some(text) = interaction_tree.text_for_element(drag.element_id) else {
+                    return Ok(());
+                };
+                let next = Some(TextSelection {
+                    element_id: drag.element_id,
+                    anchor: drag.anchor,
+                    focus: text.byte_offset_for_position(event.position),
+                });
+                if *text_selection.selection.borrow() != next {
+                    *text_selection.selection.borrow_mut() = next;
+                    selection_changed = true;
+                }
+            }
+            RoutedPointerEventKind::Up {
+                button: PointerButton::Primary,
+            } => {
+                if text_selection.drag.borrow_mut().take().is_some() {
+                    selection_changed = true;
+                }
+            }
+            _ => {}
+        }
+
+        if selection_changed {
+            text_selection.version.update(|value| *value += 1);
+            sync_primary_selection(window, interaction_tree, *text_selection.selection.borrow())?;
+        }
+
+        Ok(())
+    }
+
+    fn interaction_ids(targets: &[ruin_ui::HitTarget]) -> Vec<ruin_ui::ElementId> {
+        targets.iter().filter_map(|target| target.element_id).collect()
+    }
+
+    fn update_interaction_state(
+        input_state: &mut InputState,
+        hovered_ids: Vec<ruin_ui::ElementId>,
+        pressed_ids: Vec<ruin_ui::ElementId>,
+    ) -> 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 pressed_changed = input_state.pressed_elements.set(pressed_ids.clone()).is_some();
+        if hovered_changed || pressed_changed {
+            tracing::trace!(
+                target: "ruin_app::interaction",
+                hovered_before = ?previous_hovered,
+                hovered_after = ?hovered_ids,
+                pressed_before = ?previous_pressed,
+                pressed_after = ?pressed_ids,
+                "interaction state changed"
+            );
+        }
+        hovered_changed || pressed_changed
+    }
+}
+
+#[doc(hidden)]
+pub fn __render_mountable_for_test<M: Mountable>(mountable: &M) -> View {
+    render_with_context(Rc::new(RenderState::default()), || mountable.render()).view
+}

lib/ruin_app/src/colors.rs

@@ -0,0 +1,13 @@
+use ruin_ui::Color;
+
+pub const fn text() -> Color {
+    Color::rgb(0xFF, 0xFF, 0xFF)
+}
+
+pub const fn muted() -> Color {
+    Color::rgb(0xB6, 0xC2, 0xD9)
+}
+
+pub const fn danger() -> Color {
+    Color::rgb(0xFF, 0x7B, 0x72)
+}

lib/ruin_app/src/context.rs

@@ -0,0 +1,204 @@
+use std::any::{Any, TypeId};
+use std::cell::{Cell as StdCell, RefCell};
+use std::rc::Rc;
+
+use ruin_ui::ElementId;
+
+use crate::ContextKey;
+use crate::view::View;
+
+#[derive(Clone)]
+pub(crate) struct ContextEntry {
+    pub(crate) key: TypeId,
+    pub(crate) value: Rc<dyn Any>,
+}
+
+impl ContextEntry {
+    pub(crate) fn new<C: ContextKey>(value: C::Value) -> Self {
+        Self {
+            key: TypeId::of::<C>(),
+            value: Rc::new(value),
+        }
+    }
+}
+
+#[derive(Default)]
+pub(crate) struct RenderState {
+    pub(crate) hooks: RefCell<Vec<Box<dyn Any>>>,
+    pub(crate) element_ids: RefCell<Vec<ElementId>>,
+    pub(crate) next_element_id: StdCell<u64>,
+}
+
+#[derive(Clone, Debug, Default, PartialEq, Eq)]
+pub(crate) struct InteractionSnapshot {
+    pub(crate) hovered: Vec<ElementId>,
+    pub(crate) pressed: Vec<ElementId>,
+}
+
+#[derive(Clone, Default)]
+pub(crate) struct RenderSideEffects {
+    pub(crate) window_title: Option<String>,
+    pub(crate) shortcuts: Vec<crate::input::ShortcutBinding>,
+}
+
+#[derive(Clone)]
+pub(crate) struct RenderContext {
+    pub(crate) state: Rc<RenderState>,
+    pub(crate) hook_index: Rc<StdCell<usize>>,
+    pub(crate) element_index: Rc<StdCell<usize>>,
+    pub(crate) side_effects: Rc<RefCell<RenderSideEffects>>,
+    pub(crate) context_entries: Rc<Vec<ContextEntry>>,
+    pub(crate) interaction: Rc<InteractionSnapshot>,
+}
+
+impl RenderContext {
+    pub(crate) fn with_context_entries(&self, context_entries: Rc<Vec<ContextEntry>>) -> Self {
+        Self {
+            state: Rc::clone(&self.state),
+            hook_index: Rc::clone(&self.hook_index),
+            element_index: Rc::clone(&self.element_index),
+            side_effects: Rc::clone(&self.side_effects),
+            context_entries,
+            interaction: Rc::clone(&self.interaction),
+        }
+    }
+}
+
+pub(crate) struct RenderOutput {
+    pub(crate) view: View,
+    pub(crate) side_effects: RenderSideEffects,
+}
+
+thread_local! {
+    pub(crate) static CURRENT_RENDER_CONTEXT: RefCell<Option<RenderContext>> = const { RefCell::new(None) };
+}
+
+pub(crate) fn render_with_context(
+    state: Rc<RenderState>,
+    render: impl FnOnce() -> View,
+) -> RenderOutput {
+    render_with_context_and_interaction(state, Rc::new(InteractionSnapshot::default()), render)
+}
+
+pub(crate) fn render_with_context_and_interaction(
+    state: Rc<RenderState>,
+    interaction: Rc<InteractionSnapshot>,
+    render: impl FnOnce() -> View,
+) -> RenderOutput {
+    let context = RenderContext {
+        state,
+        hook_index: Rc::new(StdCell::new(0)),
+        element_index: Rc::new(StdCell::new(0)),
+        side_effects: Rc::new(RefCell::new(RenderSideEffects::default())),
+        context_entries: Rc::new(Vec::new()),
+        interaction,
+    };
+
+    let view = with_render_context(context.clone(), render);
+    let side_effects = context.side_effects.borrow().clone();
+    RenderOutput { view, side_effects }
+}
+
+pub(crate) fn with_render_context(
+    context: RenderContext,
+    render: impl FnOnce() -> View,
+) -> View {
+    CURRENT_RENDER_CONTEXT.with(|slot| {
+        let previous = slot.replace(Some(context.clone()));
+
+        struct Guard<'a> {
+            slot: &'a RefCell<Option<RenderContext>>,
+            previous: Option<RenderContext>,
+        }
+
+        impl Drop for Guard<'_> {
+            fn drop(&mut self) {
+                let _ = self.slot.replace(self.previous.take());
+            }
+        }
+
+        let _guard = Guard { slot, previous };
+        render()
+    })
+}
+
+pub(crate) fn with_render_context_state<R>(f: impl FnOnce(&RenderContext) -> R) -> R {
+    CURRENT_RENDER_CONTEXT.with(|slot| {
+        let context = slot
+            .borrow()
+            .clone()
+            .expect("ruin_app hooks can only run while rendering a mounted component");
+        f(&context)
+    })
+}
+
+pub(crate) fn with_hook_slot<T: 'static, R>(
+    init: impl FnOnce() -> T,
+    f: impl FnOnce(&mut T) -> R,
+) -> R {
+    with_render_context_state(|context| {
+        let index = context.hook_index.get();
+        context.hook_index.set(index + 1);
+
+        let mut hooks = context.state.hooks.borrow_mut();
+        if hooks.len() == index {
+            hooks.push(Box::new(init()));
+        }
+
+        let slot = hooks[index]
+            .downcast_mut::<T>()
+            .expect("ruin_app hook call order changed between renders");
+        f(slot)
+    })
+}
+
+pub(crate) fn allocate_element_id() -> ElementId {
+    with_render_context_state(|context| {
+        let index = context.element_index.get();
+        context.element_index.set(index + 1);
+
+        let mut element_ids = context.state.element_ids.borrow_mut();
+        if element_ids.len() == index {
+            let next = context.state.next_element_id.get().wrapping_add(1);
+            context.state.next_element_id.set(next);
+            element_ids.push(ElementId::new(next));
+        }
+        element_ids[index]
+    })
+}
+
+pub(crate) struct MemoSlot<T> {
+    pub(crate) compute: Rc<RefCell<Box<dyn Fn() -> T>>>,
+    pub(crate) handle: crate::hooks::Memo<T>,
+}
+
+pub(crate) struct ResourceSlot<T, E> {
+    pub(crate) resource: crate::hooks::Resource<T, E>,
+    pub(crate) _effect: ruin_reactivity::EffectHandle,
+}
+
+impl<T: 'static> MemoSlot<T> {
+    pub(crate) fn new(compute: Rc<RefCell<Box<dyn Fn() -> T>>>) -> Self {
+        let handle = crate::hooks::Memo {
+            compute: Rc::new({
+                let compute = Rc::clone(&compute);
+                move || {
+                    let compute = compute.borrow();
+                    (compute.as_ref())()
+                }
+            }),
+        };
+        Self { compute, handle }
+    }
+
+    pub(crate) fn replace_compute(&mut self, compute: Rc<RefCell<Box<dyn Fn() -> T>>>) {
+        self.compute = Rc::clone(&compute);
+        self.handle.compute = Rc::new({
+            let compute = Rc::clone(&compute);
+            move || {
+                let compute = compute.borrow();
+                (compute.as_ref())()
+            }
+        });
+    }
+}

lib/ruin_app/src/converters.rs

@@ -0,0 +1,43 @@
+use ruin_ui::{Border, BoxShadow, Color, Edges};
+
+pub trait IntoEdges {
+    fn into_edges(self) -> Edges;
+}
+
+impl IntoEdges for Edges {
+    fn into_edges(self) -> Edges {
+        self
+    }
+}
+
+impl IntoEdges for f32 {
+    fn into_edges(self) -> Edges {
+        Edges::all(self)
+    }
+}
+
+pub trait IntoBorder {
+    fn into_border(self) -> Border;
+}
+
+impl IntoBorder for Border {
+    fn into_border(self) -> Border {
+        self
+    }
+}
+
+impl IntoBorder for (f32, Color) {
+    fn into_border(self) -> Border {
+        Border::new(self.0, self.1)
+    }
+}
+
+pub trait IntoShadow {
+    fn into_shadow(self) -> BoxShadow;
+}
+
+impl IntoShadow for BoxShadow {
+    fn into_shadow(self) -> BoxShadow {
+        self
+    }
+}

lib/ruin_app/src/hooks.rs

@@ -0,0 +1,416 @@
+use std::any::type_name;
+use std::any::TypeId;
+use std::cell::Cell as StdCell;
+use std::future::Future;
+use std::marker::PhantomData;
+use std::rc::Rc;
+
+use ruin_ui::{ElementId, InteractionTree, KeyboardEvent, KeyboardEventKind, KeyboardKey};
+
+use crate::ContextKey;
+use crate::context::{
+    ContextEntry, MemoSlot, ResourceSlot, with_hook_slot,
+    with_render_context, with_render_context_state,
+};
+use crate::input::ShortcutBinding;
+
+pub struct SignalInner<T> {
+    pub(crate) cell: ruin_reactivity::Cell<T>,
+}
+
+pub struct Signal<T> {
+    pub(crate) inner: Rc<SignalInner<T>>,
+}
+
+impl<T> Clone for Signal<T> {
+    fn clone(&self) -> Self {
+        Self {
+            inner: Rc::clone(&self.inner),
+        }
+    }
+}
+
+impl<T: 'static> Signal<T> {
+    pub(crate) fn new(initial: T) -> Self {
+        Self {
+            inner: Rc::new(SignalInner {
+                cell: ruin_reactivity::cell(initial),
+            }),
+        }
+    }
+
+    pub fn with<R>(&self, f: impl FnOnce(&T) -> R) -> R {
+        self.inner.cell.with(f)
+    }
+
+    pub fn replace(&self, value: T) -> T {
+        self.inner.cell.replace(value)
+    }
+
+    pub fn update<R>(&self, f: impl FnOnce(&mut T) -> R) -> R {
+        self.inner.cell.update(f)
+    }
+}
+
+impl<T: Clone + 'static> Signal<T> {
+    pub fn get(&self) -> T {
+        self.inner.cell.get()
+    }
+}
+
+impl<T: PartialEq + 'static> Signal<T> {
+    pub fn set(&self, value: T) -> Option<T> {
+        self.inner.cell.set(value)
+    }
+}
+
+pub struct Memo<T> {
+    pub(crate) compute: Rc<dyn Fn() -> T>,
+}
+
+impl<T> Clone for Memo<T> {
+    fn clone(&self) -> Self {
+        Self {
+            compute: Rc::clone(&self.compute),
+        }
+    }
+}
+
+impl<T> Memo<T> {
+    pub fn with<R>(&self, f: impl FnOnce(&T) -> R) -> R {
+        let value = (self.compute)();
+        f(&value)
+    }
+}
+
+impl<T: Clone> Memo<T> {
+    pub fn get(&self) -> T {
+        (self.compute)()
+    }
+}
+
+pub fn use_signal<T: 'static>(initial: impl FnOnce() -> T) -> Signal<T> {
+    with_hook_slot(|| Signal::new(initial()), |signal| signal.clone())
+}
+
+pub fn use_context<C: ContextKey>() -> C::Value {
+    with_render_context_state(|context| {
+        context
+            .context_entries
+            .iter()
+            .rev()
+            .find_map(|entry| {
+                (entry.key == TypeId::of::<C>())
+                    .then(|| entry.value.downcast_ref::<C::Value>())
+                    .flatten()
+                    .cloned()
+            })
+            .unwrap_or_else(|| {
+                panic!(
+                    "missing context provider for {} while rendering",
+                    type_name::<C>()
+                )
+            })
+    })
+}
+
+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));
+        with_render_context(
+            context.with_context_entries(Rc::new(context_entries)),
+            render,
+        )
+    })
+}
+
+pub fn use_memo<T: 'static>(compute: impl Fn() -> T + 'static) -> Memo<T> {
+    use std::cell::RefCell;
+    let compute: Rc<RefCell<Box<dyn Fn() -> T>>> =
+        Rc::new(RefCell::new(Box::new(compute) as Box<dyn Fn() -> T>));
+    with_hook_slot(
+        {
+            let compute = Rc::clone(&compute);
+            move || MemoSlot::new(compute)
+        },
+        |slot: &mut MemoSlot<T>| {
+            slot.replace_compute(Rc::clone(&compute));
+            slot.handle.clone()
+        },
+    )
+}
+
+pub fn use_effect(effect: impl Fn() + 'static) {
+    with_hook_slot(|| ruin_reactivity::effect(effect), |_| ());
+}
+
+pub fn use_window_title(compute: impl FnOnce() -> String) {
+    with_render_context_state(|context| {
+        context.side_effects.borrow_mut().window_title = Some(compute());
+    });
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub enum Key {
+    Character(char),
+    Enter,
+    Backspace,
+    Escape,
+    Delete,
+    ArrowLeft,
+    ArrowRight,
+    ArrowUp,
+    ArrowDown,
+    Home,
+    End,
+}
+
+impl Key {
+    pub(crate) fn matches(&self, event: &KeyboardEvent) -> bool {
+        match (self, &event.key) {
+            (Self::Character(expected), KeyboardKey::Character(actual)) => actual
+                .chars()
+                .next()
+                .is_some_and(|actual| actual.eq_ignore_ascii_case(expected)),
+            (Self::Enter, KeyboardKey::Enter) => true,
+            (Self::Backspace, KeyboardKey::Backspace) => true,
+            (Self::Escape, KeyboardKey::Escape) => true,
+            (Self::Delete, KeyboardKey::Delete) => true,
+            (Self::ArrowLeft, KeyboardKey::ArrowLeft) => true,
+            (Self::ArrowRight, KeyboardKey::ArrowRight) => true,
+            (Self::ArrowUp, KeyboardKey::ArrowUp) => true,
+            (Self::ArrowDown, KeyboardKey::ArrowDown) => true,
+            (Self::Home, KeyboardKey::Home) => true,
+            (Self::End, KeyboardKey::End) => true,
+            _ => false,
+        }
+    }
+}
+
+#[derive(Clone, Debug, Eq, PartialEq)]
+pub struct Shortcut {
+    pub(crate) key: Key,
+    pub(crate) control: bool,
+    pub(crate) shift: bool,
+    pub(crate) alt: bool,
+    pub(crate) super_key: bool,
+}
+
+impl Shortcut {
+    pub fn new(key: Key) -> Self {
+        Self {
+            key,
+            control: false,
+            shift: false,
+            alt: false,
+            super_key: false,
+        }
+    }
+
+    pub fn with_ctrl(mut self) -> Self {
+        self.control = true;
+        self
+    }
+
+    pub fn with_shift(mut self) -> Self {
+        self.shift = true;
+        self
+    }
+
+    pub(crate) fn matches(&self, event: &KeyboardEvent) -> bool {
+        if event.kind != KeyboardEventKind::Pressed {
+            return false;
+        }
+        if !self.key.matches(event) {
+            return false;
+        }
+        if event.modifiers.control != self.control {
+            return false;
+        }
+        if event.modifiers.alt != self.alt {
+            return false;
+        }
+        if event.modifiers.super_key != self.super_key {
+            return false;
+        }
+        // For character shortcuts the produced character already encodes the shift
+        // state, so don't additionally require that Shift is (un)held.
+        if !matches!(self.key, Key::Character(_)) && event.modifiers.shift != self.shift {
+            return false;
+        }
+        true
+    }
+}
+
+#[derive(Clone)]
+pub struct FocusScope {
+    pub(crate) element_id: Signal<Option<ElementId>>,
+}
+
+#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
+pub struct InteractionState {
+    pub hovered: bool,
+    pub pressed: bool,
+}
+
+#[derive(Clone)]
+pub enum ShortcutScope {
+    Application,
+    FocusedWithin(FocusScope),
+}
+
+impl ShortcutScope {
+    pub(crate) fn matches(
+        &self,
+        focused_element: Option<ElementId>,
+        interaction_tree: &InteractionTree,
+    ) -> bool {
+        match self {
+            Self::Application => true,
+            Self::FocusedWithin(scope) => {
+                let Some(scope_element) = scope.element_id.get() else {
+                    return false;
+                };
+                let Some(focused_element) = focused_element else {
+                    return false;
+                };
+                crate::input::element_contains_element(
+                    interaction_tree,
+                    scope_element,
+                    focused_element,
+                )
+            }
+        }
+    }
+}
+
+pub struct WidgetRef<T> {
+    pub(crate) element_id: Signal<Option<ElementId>>,
+    pub(crate) _marker: PhantomData<fn() -> T>,
+}
+
+impl<T> Clone for WidgetRef<T> {
+    fn clone(&self) -> Self {
+        Self {
+            element_id: self.element_id.clone(),
+            _marker: PhantomData,
+        }
+    }
+}
+
+impl<T> WidgetRef<T> {
+    pub(crate) fn new() -> Self {
+        Self {
+            element_id: Signal::new(None),
+            _marker: PhantomData,
+        }
+    }
+
+    pub fn element_id(&self) -> Option<ElementId> {
+        self.element_id.get()
+    }
+
+    pub fn focus_scope(&self) -> FocusScope {
+        FocusScope {
+            element_id: self.element_id.clone(),
+        }
+    }
+}
+
+pub struct ScrollBoxWidget;
+pub struct BlockWidget;
+
+pub fn use_widget_ref<T: 'static>() -> WidgetRef<T> {
+    with_hook_slot(WidgetRef::new, |widget_ref: &mut WidgetRef<T>| {
+        widget_ref.clone()
+    })
+}
+
+pub fn use_interaction_state<T: 'static>(widget_ref: WidgetRef<T>) -> InteractionState {
+    with_render_context_state(|context| {
+        let Some(element_id) = widget_ref.element_id() else {
+            return InteractionState::default();
+        };
+        InteractionState {
+            hovered: context.interaction.hovered.contains(&element_id),
+            pressed: context.interaction.pressed.contains(&element_id),
+        }
+    })
+}
+
+pub fn use_shortcut(shortcut: Shortcut, scope: ShortcutScope, action: impl Fn() + 'static) {
+    use_shortcut_with_context(shortcut, scope, move |_| action());
+}
+
+pub fn use_shortcut_with_context(
+    shortcut: Shortcut,
+    scope: ShortcutScope,
+    action: impl Fn(&InteractionTree) + 'static,
+) {
+    with_render_context_state(|context| {
+        context
+            .side_effects
+            .borrow_mut()
+            .shortcuts
+            .push(ShortcutBinding {
+                shortcut,
+                scope,
+                action: Rc::new(action),
+            });
+    });
+}
+
+#[derive(Clone)]
+pub struct Resource<T, E> {
+    pub(crate) state: Signal<ResourceState<T, E>>,
+}
+
+impl<T: Clone + 'static, E: Clone + 'static> Resource<T, E> {
+    pub fn read(&self) -> ResourceState<T, E> {
+        self.state.get()
+    }
+}
+
+#[derive(Clone)]
+pub enum ResourceState<T, E> {
+    Pending,
+    Ready(std::result::Result<T, E>),
+}
+
+pub fn use_resource<T, E, Fut, F>(factory: F) -> Resource<T, E>
+where
+    T: Clone + 'static,
+    E: Clone + 'static,
+    Fut: Future<Output = std::result::Result<T, E>> + 'static,
+    F: Fn() -> Fut + 'static,
+{
+    with_hook_slot(
+        || {
+            let resource = Resource {
+                state: Signal::new(ResourceState::Pending),
+            };
+            let generation = Rc::new(StdCell::new(0_u64));
+            let _effect = ruin_reactivity::effect({
+                let resource = resource.clone();
+                let generation = Rc::clone(&generation);
+                move || {
+                    let next_generation = generation.get().wrapping_add(1);
+                    generation.set(next_generation);
+                    let _ = resource.state.replace(ResourceState::Pending);
+                    let resource = resource.clone();
+                    let future = factory();
+                    let generation = Rc::clone(&generation);
+                    std::mem::drop(ruin_runtime::queue_future(async move {
+                        let result = future.await;
+                        if generation.get() == next_generation {
+                            let _ = resource.state.replace(ResourceState::Ready(result));
+                        }
+                    }));
+                }
+            });
+            ResourceSlot { resource, _effect }
+        },
+        |slot: &mut ResourceSlot<T, E>| slot.resource.clone(),
+    )
+}

lib/ruin_app/src/input.rs

@@ -0,0 +1,350 @@
+use std::cell::RefCell;
+use std::collections::HashMap;
+use std::rc::Rc;
+
+use ruin_ui::{
+    CursorIcon, DisplayItem, ElementId, HitTarget, InteractionTree, KeyboardEvent,
+    PointerButton, PointerEvent, Quad, RoutedPointerEvent,
+    RoutedPointerEventKind, WindowController,
+};
+
+use crate::hooks::{Shortcut, ShortcutScope, Signal};
+use crate::view::View;
+
+pub(crate) type PressHandler = Rc<dyn Fn(&RoutedPointerEvent) + 'static>;
+pub(crate) type ScrollHandler = Rc<dyn Fn(&RoutedPointerEvent, &InteractionTree) + 'static>;
+pub(crate) type KeyHandler = Rc<dyn Fn(&KeyboardEvent, &InteractionTree) -> bool + 'static>;
+
+#[derive(Clone, Default)]
+pub(crate) struct EventBindings {
+    pub(crate) on_press: HashMap<ElementId, PressHandler>,
+    pub(crate) on_scroll: HashMap<ElementId, ScrollHandler>,
+    pub(crate) on_key: HashMap<ElementId, KeyHandler>,
+}
+
+impl EventBindings {
+    pub(crate) fn extend(&mut self, other: EventBindings) {
+        self.on_press.extend(other.on_press);
+        self.on_scroll.extend(other.on_scroll);
+        self.on_key.extend(other.on_key);
+    }
+
+    pub(crate) fn dispatch(
+        &self,
+        event: &RoutedPointerEvent,
+        interaction_tree: &InteractionTree,
+        hovered_targets: &[HitTarget],
+    ) {
+        match event.kind {
+            RoutedPointerEventKind::Up {
+                button: PointerButton::Primary,
+            } => {
+                if let Some(element_id) = event.target.element_id
+                    && let Some(handler) = self.on_press.get(&element_id)
+                {
+                    handler(event);
+                }
+                if let Some(handler) = scroll_handler_for_event(
+                    &self.on_scroll,
+                    event.target.element_id,
+                    hovered_targets,
+                ) {
+                    handler(event, interaction_tree);
+                }
+            }
+            RoutedPointerEventKind::Down {
+                button: PointerButton::Primary,
+            }
+            | RoutedPointerEventKind::Move
+            | RoutedPointerEventKind::Scroll { .. }
+            | RoutedPointerEventKind::Leave => {
+                if let Some(handler) = scroll_handler_for_event(
+                    &self.on_scroll,
+                    event.target.element_id,
+                    hovered_targets,
+                ) {
+                    handler(event, interaction_tree);
+                }
+            }
+            _ => {}
+        }
+    }
+
+    pub(crate) fn dispatch_key(
+        &self,
+        focused_element: Option<ElementId>,
+        event: &KeyboardEvent,
+        interaction_tree: &InteractionTree,
+    ) {
+        let Some(handler) =
+            key_handler_for_focus(&self.on_key, focused_element, interaction_tree)
+        else {
+            return;
+        };
+        let _ = handler(event, interaction_tree);
+    }
+}
+
+#[derive(Clone, Copy, PartialEq)]
+pub(crate) struct ScrollbarDrag {
+    pub(crate) start_pointer_y: f32,
+    pub(crate) start_offset_y: f32,
+}
+
+#[derive(Clone, Copy, PartialEq)]
+pub(crate) struct TextSelection {
+    pub(crate) element_id: ElementId,
+    pub(crate) anchor: usize,
+    pub(crate) focus: usize,
+}
+
+#[derive(Clone, Copy, PartialEq)]
+pub(crate) struct TextSelectionDrag {
+    pub(crate) element_id: ElementId,
+    pub(crate) anchor: usize,
+}
+
+pub(crate) struct TextSelectionState {
+    pub(crate) selection: RefCell<Option<TextSelection>>,
+    pub(crate) drag: RefCell<Option<TextSelectionDrag>>,
+    pub(crate) version: Signal<u64>,
+}
+
+impl TextSelectionState {
+    pub(crate) fn new() -> Self {
+        Self {
+            selection: RefCell::new(None),
+            drag: RefCell::new(None),
+            version: Signal::new(0),
+        }
+    }
+}
+
+pub(crate) struct InputState {
+    pub(crate) current_cursor: CursorIcon,
+    pub(crate) focused_element: Option<ElementId>,
+    pub(crate) text_selection: Rc<TextSelectionState>,
+    pub(crate) hovered_elements: Signal<Vec<ElementId>>,
+    pub(crate) pressed_elements: Signal<Vec<ElementId>>,
+    pub(crate) interaction_version: Signal<u64>,
+}
+
+impl InputState {
+    pub(crate) fn new() -> Self {
+        Self {
+            current_cursor: CursorIcon::Default,
+            focused_element: None,
+            text_selection: Rc::new(TextSelectionState::new()),
+            hovered_elements: Signal::new(Vec::new()),
+            pressed_elements: Signal::new(Vec::new()),
+            interaction_version: Signal::new(0),
+        }
+    }
+}
+
+#[derive(Clone)]
+pub(crate) struct ShortcutBinding {
+    pub(crate) shortcut: Shortcut,
+    pub(crate) scope: ShortcutScope,
+    pub(crate) action: Rc<dyn Fn(&InteractionTree)>,
+}
+
+impl ShortcutBinding {
+    pub(crate) fn matches(
+        &self,
+        event: &KeyboardEvent,
+        focused_element: Option<ElementId>,
+        interaction_tree: &InteractionTree,
+    ) -> bool {
+        self.shortcut.matches(event) && self.scope.matches(focused_element, interaction_tree)
+    }
+
+    pub(crate) fn trigger(&self, interaction_tree: &InteractionTree) {
+        (self.action)(interaction_tree);
+    }
+}
+
+pub(crate) fn clamp_scroll_offset(offset_y: f32, max_offset_y: f32) -> f32 {
+    offset_y.clamp(0.0, max_offset_y.max(0.0))
+}
+
+pub(crate) fn apply_text_selection_overlay(
+    scene: &mut ruin_ui::SceneSnapshot,
+    selection: Option<TextSelection>,
+) {
+    let Some(selection) = selection else {
+        return;
+    };
+
+    let mut next_items = Vec::with_capacity(scene.items.len());
+    for item in scene.items.drain(..) {
+        match item {
+            DisplayItem::Text(mut text) if text.element_id == Some(selection.element_id) => {
+                for rect in text.selection_rects(selection.anchor, selection.focus) {
+                    next_items.push(DisplayItem::Quad(Quad::new(
+                        rect,
+                        text.selection_style.highlight_color,
+                    )));
+                }
+                text.apply_selected_text_color(selection.anchor, selection.focus);
+                next_items.push(DisplayItem::Text(text));
+            }
+            other => next_items.push(other),
+        }
+    }
+    scene.items = next_items;
+}
+
+pub(crate) fn sync_primary_selection(
+    window: &WindowController,
+    interaction_tree: &InteractionTree,
+    selection: Option<TextSelection>,
+) -> crate::Result<()> {
+    let Some(selection) = selection else {
+        window.set_primary_selection_text(String::new())?;
+        return Ok(());
+    };
+
+    let Some(text) = interaction_tree.text_for_element(selection.element_id) else {
+        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>(
+    handlers: &'a HashMap<ElementId, ScrollHandler>,
+    direct_target: Option<ElementId>,
+    hovered_targets: &[HitTarget],
+) -> Option<&'a ScrollHandler> {
+    if let Some(element_id) = direct_target
+        && let Some(handler) = handlers.get(&element_id)
+    {
+        return Some(handler);
+    }
+
+    hovered_targets
+        .iter()
+        .rev()
+        .filter_map(|target| target.element_id)
+        .find_map(|element_id| handlers.get(&element_id))
+}
+
+pub(crate) fn focused_element_for_pointer(
+    interaction_tree: &InteractionTree,
+    event: &PointerEvent,
+) -> Option<ElementId> {
+    let hit_path = interaction_tree.hit_path(event.position);
+    hit_path
+        .iter()
+        .rev()
+        .find_map(|target| target.focusable.then_some(target.element_id).flatten())
+        .or_else(|| hit_path.iter().rev().find_map(|target| target.element_id))
+}
+
+pub(crate) fn element_contains_element(
+    interaction_tree: &InteractionTree,
+    ancestor: ElementId,
+    descendant: ElementId,
+) -> bool {
+    fn contains_descendant(node: &ruin_ui::LayoutNode, descendant: ElementId) -> bool {
+        if node.element_id == Some(descendant) {
+            return true;
+        }
+        node.children
+            .iter()
+            .any(|child| contains_descendant(child, descendant))
+    }
+
+    fn ancestor_contains(
+        node: &ruin_ui::LayoutNode,
+        ancestor: ElementId,
+        descendant: ElementId,
+    ) -> bool {
+        if node.element_id == Some(ancestor) {
+            return contains_descendant(node, descendant);
+        }
+        node.children
+            .iter()
+            .any(|child| ancestor_contains(child, ancestor, descendant))
+    }
+
+    ancestor_contains(&interaction_tree.root, ancestor, descendant)
+}
+
+pub(crate) fn key_handler_for_focus<'a>(
+    handlers: &'a HashMap<ElementId, KeyHandler>,
+    focused_element: Option<ElementId>,
+    interaction_tree: &InteractionTree,
+) -> Option<&'a KeyHandler> {
+    let focused_element = focused_element?;
+    focused_ancestor_chain(&interaction_tree.root, focused_element)?
+        .into_iter()
+        .find_map(|element_id| handlers.get(&element_id))
+}
+
+pub(crate) fn focused_ancestor_chain(
+    node: &ruin_ui::LayoutNode,
+    focused_element: ElementId,
+) -> Option<Vec<ElementId>> {
+    let mut chain = Vec::new();
+    if build_focused_ancestor_chain(node, focused_element, &mut chain) {
+        Some(chain)
+    } else {
+        None
+    }
+}
+
+pub(crate) fn build_focused_ancestor_chain(
+    node: &ruin_ui::LayoutNode,
+    focused_element: ElementId,
+    chain: &mut Vec<ElementId>,
+) -> bool {
+    if node.element_id == Some(focused_element) {
+        if let Some(element_id) = node.element_id {
+            chain.push(element_id);
+        }
+        return true;
+    }
+
+    for child in &node.children {
+        if build_focused_ancestor_chain(child, focused_element, chain) {
+            if let Some(element_id) = node.element_id {
+                chain.push(element_id);
+            }
+            return true;
+        }
+    }
+
+    false
+}
+
+// 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 {
+        self.bindings.on_press.insert(element_id, handler);
+        self
+    }
+
+    pub(crate) fn with_scroll_handler(
+        mut self,
+        element_id: ElementId,
+        handler: ScrollHandler,
+    ) -> Self {
+        self.bindings.on_scroll.insert(element_id, handler);
+        self
+    }
+
+    pub(crate) fn with_key_handler(
+        mut self,
+        element_id: ElementId,
+        handler: KeyHandler,
+    ) -> Self {
+        self.bindings.on_key.insert(element_id, handler);
+        self
+    }
+}

lib/ruin_app/src/primitives/button.rs

@@ -0,0 +1,69 @@
+use std::rc::Rc;
+
+use ruin_ui::{CursorIcon, Edges, Element, RoutedPointerEvent};
+
+use crate::context::allocate_element_id;
+use crate::input::PressHandler;
+use crate::primitives::ContainerProps;
+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,
+    pub(crate) on_press: Option<PressHandler>,
+}
+
+pub fn button() -> ButtonBuilder {
+    ButtonBuilder {
+        props: ContainerProps::new(
+            Element::column()
+                .padding(Edges::symmetric(14.0, 10.0))
+                .background(surfaces::interactive())
+                .corner_radius(10.0)
+                .cursor(CursorIcon::Pointer)
+                .focusable(true),
+        ),
+        on_press: None,
+    }
+}
+
+impl ButtonBuilder {
+    impl_props_methods!();
+
+    pub fn shadow(mut self, shadow: impl crate::converters::IntoShadow) -> Self {
+        self.props = self.props.shadow(shadow);
+        self
+    }
+
+    pub fn on_press(mut self, handler: impl Fn(&RoutedPointerEvent) + 'static) -> Self {
+        self.on_press = Some(Rc::new(handler));
+        self
+    }
+
+    pub fn text_style(mut self, style: crate::text_style::PartialTextStyle) -> Self {
+        self.props = self.props.text_style(style);
+        self
+    }
+
+    pub fn children(mut self, children: impl Children) -> View {
+        let id = allocate_element_id();
+        self.props.element = self.props.element.id(id);
+        if let Some(widget_ref) = &self.props.widget_ref {
+            let _ = widget_ref.set(Some(id));
+        }
+        let had_style = self.props.partial_text_style.is_some();
+        if let Some(style) = self.props.partial_text_style.take() {
+            push_text_style(style);
+        }
+        let children_views = children.into_views();
+        if had_style {
+            pop_text_style();
+        }
+        let view = View::from_container(self.props.element, children_views);
+        match self.on_press {
+            Some(handler) => view.with_press_handler(id, handler),
+            None => view,
+        }
+    }
+}

lib/ruin_app/src/primitives/container.rs

@@ -0,0 +1,157 @@
+use ruin_ui::{AlignItems, Color, Element, ElementId};
+
+use crate::context::allocate_element_id;
+use crate::converters::{IntoBorder, IntoEdges, IntoShadow};
+use crate::hooks::{Signal, WidgetRef};
+use crate::text_style::{PartialTextStyle, pop_text_style, push_text_style};
+use crate::view::{Children, View};
+
+/// Shared box-model properties common to all container-like builders.
+pub struct ContainerProps {
+    pub(crate) element: Element,
+    pub(crate) widget_ref: Option<Signal<Option<ElementId>>>,
+    pub(crate) partial_text_style: Option<PartialTextStyle>,
+}
+
+impl ContainerProps {
+    pub(crate) fn new(element: Element) -> Self {
+        Self {
+            element,
+            widget_ref: None,
+            partial_text_style: None,
+        }
+    }
+
+    pub fn text_style(mut self, style: PartialTextStyle) -> Self {
+        self.partial_text_style = Some(style);
+        self
+    }
+
+    pub fn gap(mut self, gap: f32) -> Self {
+        self.element = self.element.gap(gap);
+        self
+    }
+
+    pub fn padding(mut self, padding: impl IntoEdges) -> Self {
+        self.element = self.element.padding(padding.into_edges());
+        self
+    }
+
+    pub fn background(mut self, color: Color) -> Self {
+        self.element = self.element.background(color);
+        self
+    }
+
+    pub fn border(mut self, border: impl IntoBorder) -> Self {
+        let border = border.into_border();
+        self.element = self.element.border(border.width, border.color);
+        self
+    }
+
+    pub fn border_radius(mut self, radius: f32) -> Self {
+        self.element = self.element.corner_radius(radius);
+        self
+    }
+
+    pub fn width(mut self, width: f32) -> Self {
+        self.element = self.element.width(width);
+        self
+    }
+
+    pub fn height(mut self, height: f32) -> Self {
+        self.element = self.element.height(height);
+        self
+    }
+
+    pub fn min_width(mut self, min_width: f32) -> Self {
+        self.element = self.element.min_width(min_width);
+        self
+    }
+
+    pub fn min_height(mut self, min_height: f32) -> Self {
+        self.element = self.element.min_height(min_height);
+        self
+    }
+
+    pub fn min_size(self, w: f32, h: f32) -> Self {
+        self.min_width(w).min_height(h)
+    }
+
+    pub fn flex(mut self, flex: f32) -> Self {
+        self.element = self.element.flex(flex);
+        self
+    }
+
+    pub fn align_items(mut self, align: AlignItems) -> Self {
+        self.element = self.element.align_items(align);
+        self
+    }
+
+    pub fn align_self(mut self, align: AlignItems) -> Self {
+        self.element = self.element.align_self(align);
+        self
+    }
+
+    pub fn shadow(mut self, shadow: impl IntoShadow) -> Self {
+        self.element = self.element.shadow(shadow.into_shadow());
+        self
+    }
+
+    pub fn widget_ref<T>(mut self, widget_ref: WidgetRef<T>) -> Self {
+        self.widget_ref = Some(widget_ref.element_id.clone());
+        self
+    }
+}
+
+pub struct ContainerBuilder {
+    pub(crate) props: ContainerProps,
+}
+
+pub fn column() -> ContainerBuilder {
+    ContainerBuilder {
+        props: ContainerProps::new(Element::column()),
+    }
+}
+
+pub fn row() -> ContainerBuilder {
+    ContainerBuilder {
+        props: ContainerProps::new(Element::row()),
+    }
+}
+
+pub fn block() -> ContainerBuilder {
+    ContainerBuilder {
+        props: ContainerProps::new(Element::column()),
+    }
+}
+
+impl ContainerBuilder {
+    impl_props_methods!();
+
+    pub fn shadow(mut self, shadow: impl IntoShadow) -> Self {
+        self.props = self.props.shadow(shadow);
+        self
+    }
+
+    pub fn text_style(mut self, style: PartialTextStyle) -> Self {
+        self.props = self.props.text_style(style);
+        self
+    }
+
+    pub fn children(mut self, children: impl Children) -> View {
+        if let Some(widget_ref) = &self.props.widget_ref {
+            let element_id = allocate_element_id();
+            self.props.element = self.props.element.id(element_id);
+            let _ = widget_ref.set(Some(element_id));
+        }
+        let had_style = self.props.partial_text_style.is_some();
+        if let Some(style) = self.props.partial_text_style.take() {
+            push_text_style(style);
+        }
+        let children_views = children.into_views();
+        if had_style {
+            pop_text_style();
+        }
+        View::from_container(self.props.element, children_views)
+    }
+}

lib/ruin_app/src/primitives/mod.rs

@@ -0,0 +1,71 @@
+/// Generates builder methods that delegate to a `props: ContainerProps` field.
+/// Must be invoked inside an `impl SomeBuilder { ... }` block.
+macro_rules! impl_props_methods {
+    () => {
+        pub fn gap(mut self, gap: f32) -> Self {
+            self.props = self.props.gap(gap);
+            self
+        }
+        pub fn padding(mut self, padding: impl $crate::converters::IntoEdges) -> Self {
+            self.props = self.props.padding(padding);
+            self
+        }
+        pub fn background(mut self, color: ruin_ui::Color) -> Self {
+            self.props = self.props.background(color);
+            self
+        }
+        pub fn border(mut self, border: impl $crate::converters::IntoBorder) -> Self {
+            self.props = self.props.border(border);
+            self
+        }
+        pub fn border_radius(mut self, radius: f32) -> Self {
+            self.props = self.props.border_radius(radius);
+            self
+        }
+        pub fn width(mut self, width: f32) -> Self {
+            self.props = self.props.width(width);
+            self
+        }
+        pub fn height(mut self, height: f32) -> Self {
+            self.props = self.props.height(height);
+            self
+        }
+        pub fn min_width(mut self, min_width: f32) -> Self {
+            self.props = self.props.min_width(min_width);
+            self
+        }
+        pub fn min_height(mut self, min_height: f32) -> Self {
+            self.props = self.props.min_height(min_height);
+            self
+        }
+        pub fn min_size(self, w: f32, h: f32) -> Self {
+            self.min_width(w).min_height(h)
+        }
+        pub fn flex(mut self, flex: f32) -> Self {
+            self.props = self.props.flex(flex);
+            self
+        }
+        pub fn align_items(mut self, align: ruin_ui::AlignItems) -> Self {
+            self.props = self.props.align_items(align);
+            self
+        }
+        pub fn align_self(mut self, align: ruin_ui::AlignItems) -> Self {
+            self.props = self.props.align_self(align);
+            self
+        }
+        pub fn widget_ref<T>(mut self, widget_ref: $crate::hooks::WidgetRef<T>) -> Self {
+            self.props = self.props.widget_ref(widget_ref);
+            self
+        }
+    };
+}
+
+pub mod button;
+pub mod container;
+pub mod scroll_box;
+pub mod text;
+
+pub use button::{ButtonBuilder, button};
+pub use container::{ContainerBuilder, ContainerProps, block, column, row};
+pub use scroll_box::{ScrollBoxBuilder, scroll_box};
+pub use text::{FontWeight, TextBuilder, TextRole, text};

lib/ruin_app/src/primitives/scroll_box.rs

@@ -0,0 +1,160 @@
+use std::rc::Rc;
+
+use ruin_ui::{Element, KeyboardEventKind, PointerButton, RoutedPointerEventKind, ScrollbarStyle};
+
+use crate::context::{allocate_element_id, with_hook_slot};
+use crate::hooks::Signal;
+use crate::input::{ScrollbarDrag, clamp_scroll_offset};
+use crate::primitives::ContainerProps;
+use crate::text_style::{pop_text_style, push_text_style};
+use crate::view::{Children, View};
+
+pub struct ScrollBoxBuilder {
+    pub(crate) props: ContainerProps,
+    pub(crate) offset_y: Option<Signal<f32>>,
+    pub(crate) drag: Signal<Option<ScrollbarDrag>>,
+}
+
+pub fn scroll_box() -> ScrollBoxBuilder {
+    ScrollBoxBuilder {
+        props: ContainerProps::new(Element::scroll_box(0.0)),
+        offset_y: None,
+        drag: with_hook_slot(|| Signal::new(None::<ScrollbarDrag>), |drag| drag.clone()),
+    }
+}
+
+impl ScrollBoxBuilder {
+    impl_props_methods!();
+
+    pub fn text_style(mut self, style: crate::text_style::PartialTextStyle) -> Self {
+        self.props = self.props.text_style(style);
+        self
+    }
+
+    pub fn scrollbar_style(mut self, style: ScrollbarStyle) -> Self {
+        self.props.element = self.props.element.scrollbar_style(style);
+        self
+    }
+
+    pub fn offset_y(mut self, offset_y: Signal<f32>) -> Self {
+        self.props.element = self.props.element.scroll_offset(offset_y.get());
+        self.offset_y = Some(offset_y);
+        self
+    }
+
+    pub fn children(mut self, children: impl Children) -> View {
+        let element_id = allocate_element_id();
+        self.props.element = self.props.element.id(element_id);
+        if let Some(widget_ref) = &self.props.widget_ref {
+            let _ = widget_ref.set(Some(element_id));
+        }
+
+        let had_style = self.props.partial_text_style.is_some();
+        if let Some(style) = self.props.partial_text_style.take() {
+            push_text_style(style);
+        }
+        let children_views = children.into_views();
+        if had_style {
+            pop_text_style();
+        }
+        let mut view = View::from_container(self.props.element, children_views);
+        if let Some(offset_y) = self.offset_y {
+            let drag = self.drag;
+            let offset_y_for_pointer = offset_y.clone();
+            let offset_y_for_keys = offset_y.clone();
+            view = view.with_scroll_handler(
+                element_id,
+                Rc::new(move |event, interaction_tree| {
+                    let Some(metrics) = interaction_tree.scroll_metrics_for_element(element_id)
+                    else {
+                        return;
+                    };
+
+                    match event.kind {
+                        RoutedPointerEventKind::Scroll { delta } => {
+                            offset_y_for_pointer.update(|value| {
+                                *value =
+                                    clamp_scroll_offset(*value + delta.y, metrics.max_offset_y);
+                            });
+                        }
+                        RoutedPointerEventKind::Down {
+                            button: PointerButton::Primary,
+                        } => {
+                            let Some(thumb_rect) = metrics.scrollbar_thumb else {
+                                return;
+                            };
+                            if !thumb_rect.contains(event.position) {
+                                return;
+                            }
+                            let _ = drag.set(Some(ScrollbarDrag {
+                                start_pointer_y: event.position.y,
+                                start_offset_y: offset_y_for_pointer.get(),
+                            }));
+                        }
+                        RoutedPointerEventKind::Move => {
+                            let Some(drag_state) = drag.get() else {
+                                return;
+                            };
+                            let Some(track_rect) = metrics.scrollbar_track else {
+                                return;
+                            };
+                            let Some(thumb_rect) = metrics.scrollbar_thumb else {
+                                return;
+                            };
+                            let thumb_travel =
+                                (track_rect.size.height - thumb_rect.size.height).max(0.0);
+                            if thumb_travel <= 0.0 || metrics.max_offset_y <= 0.0 {
+                                return;
+                            }
+                            let pointer_delta = event.position.y - drag_state.start_pointer_y;
+                            let next_offset = drag_state.start_offset_y
+                                + pointer_delta * (metrics.max_offset_y / thumb_travel);
+                            offset_y_for_pointer.update(|value| {
+                                *value = clamp_scroll_offset(next_offset, metrics.max_offset_y);
+                            });
+                        }
+                        RoutedPointerEventKind::Up {
+                            button: PointerButton::Primary,
+                        } => {
+                            let _ = drag.set(None);
+                        }
+                        _ => {}
+                    }
+                }),
+            );
+            view = view.with_key_handler(
+                element_id,
+                Rc::new(move |event, interaction_tree| {
+                    if event.kind != KeyboardEventKind::Pressed
+                        || event.modifiers.control
+                        || event.modifiers.alt
+                        || event.modifiers.super_key
+                    {
+                        return false;
+                    }
+
+                    let Some(metrics) = interaction_tree.scroll_metrics_for_element(element_id)
+                    else {
+                        return false;
+                    };
+
+                    let line_step = (metrics.viewport_rect.size.height * 0.12).clamp(28.0, 52.0);
+                    let next_offset = match event.key {
+                        ruin_ui::KeyboardKey::ArrowUp => offset_y_for_keys.get() - line_step,
+                        ruin_ui::KeyboardKey::ArrowDown => offset_y_for_keys.get() + line_step,
+                        ruin_ui::KeyboardKey::Home => 0.0,
+                        ruin_ui::KeyboardKey::End => metrics.max_offset_y,
+                        _ => return false,
+                    };
+                    let next_offset = clamp_scroll_offset(next_offset, metrics.max_offset_y);
+                    let changed = (offset_y_for_keys.get() - next_offset).abs() > f32::EPSILON;
+                    if changed {
+                        let _ = offset_y_for_keys.set(next_offset);
+                    }
+                    changed
+                }),
+            );
+        }
+        view
+    }
+}

lib/ruin_app/src/primitives/text.rs

@@ -0,0 +1,129 @@
+use ruin_ui::{Color, Element, TextFontFamily, TextSpan, TextSpanWeight, TextStyle, TextWrap};
+
+use crate::colors;
+use crate::context::allocate_element_id;
+use crate::text_style::current_text_style;
+use crate::view::{TextChildren, View};
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum TextRole {
+    Body,
+    Heading(u8),
+}
+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum FontWeight {
+    Normal,
+    Medium,
+    Semibold,
+    Bold,
+}
+
+impl FontWeight {
+    pub(crate) const fn to_text_span_weight(self) -> TextSpanWeight {
+        match self {
+            Self::Normal => TextSpanWeight::Normal,
+            Self::Medium => TextSpanWeight::Medium,
+            Self::Semibold => TextSpanWeight::Semibold,
+            Self::Bold => TextSpanWeight::Bold,
+        }
+    }
+}
+
+#[derive(Default)]
+pub struct TextBuilder {
+    pub(crate) role: Option<TextRole>,
+    pub(crate) size: Option<f32>,
+    pub(crate) weight: Option<FontWeight>,
+    pub(crate) color: Option<Color>,
+    pub(crate) font_family: Option<TextFontFamily>,
+    pub(crate) wrap: Option<TextWrap>,
+    pub(crate) selectable: Option<bool>,
+    pub(crate) pointer_events: Option<bool>,
+}
+
+pub fn text() -> TextBuilder {
+    TextBuilder::default()
+}
+
+impl TextBuilder {
+    pub fn role(mut self, role: TextRole) -> Self {
+        self.role = Some(role);
+        self
+    }
+
+    pub fn size(mut self, size: f32) -> Self {
+        self.size = Some(size);
+        self
+    }
+
+    pub fn weight(mut self, weight: FontWeight) -> Self {
+        self.weight = Some(weight);
+        self
+    }
+
+    pub fn color(mut self, color: Color) -> Self {
+        self.color = Some(color);
+        self
+    }
+
+    pub fn font_family(mut self, family: TextFontFamily) -> Self {
+        self.font_family = Some(family);
+        self
+    }
+
+    pub fn wrap(mut self, wrap: TextWrap) -> Self {
+        self.wrap = Some(wrap);
+        self
+    }
+
+    pub fn selectable(mut self, selectable: bool) -> Self {
+        self.selectable = Some(selectable);
+        self
+    }
+
+    pub fn pointer_events(mut self, pointer_events: bool) -> Self {
+        self.pointer_events = Some(pointer_events);
+        self
+    }
+
+    pub fn children(self, children: impl TextChildren) -> View {
+        let inherited = current_text_style();
+
+        let role = self.role.unwrap_or(TextRole::Body);
+        let size = self.size.or(inherited.size).unwrap_or(match role {
+            TextRole::Body => 18.0,
+            TextRole::Heading(1) => 32.0,
+            TextRole::Heading(2) => 28.0,
+            TextRole::Heading(_) => 24.0,
+        });
+        let color = self.color.or(inherited.color).unwrap_or(colors::text());
+        let weight = self.weight.or(inherited.weight).unwrap_or(match role {
+            TextRole::Body => FontWeight::Normal,
+            TextRole::Heading(_) => FontWeight::Semibold,
+        });
+        let wrap = self.wrap.or(inherited.wrap).unwrap_or(TextWrap::None);
+        let line_height = inherited.line_height.unwrap_or(size * 1.2);
+
+        let mut style = TextStyle::new(size, color)
+            .with_line_height(line_height)
+            .with_wrap(wrap);
+
+        let font_family = self.font_family.or(inherited.font_family);
+        if let Some(font_family) = font_family {
+            style = style.with_font_family(font_family);
+        }
+
+        let span = TextSpan::new(children.into_text())
+            .color(color)
+            .weight(weight.to_text_span_weight());
+        View::from_element(
+            Element::spans(
+                [span],
+                style.with_selectable(self.selectable.unwrap_or(true)),
+            )
+            .pointer_events(self.pointer_events.unwrap_or(true))
+            .id(allocate_element_id()),
+        )
+    }
+}

lib/ruin_app/src/surfaces.rs

@@ -0,0 +1,17 @@
+use ruin_ui::Color;
+
+pub const fn canvas() -> Color {
+    Color::rgb(0x0F, 0x16, 0x25)
+}
+
+pub const fn raised() -> Color {
+    Color::rgb(0x1B, 0x26, 0x3D)
+}
+
+pub const fn interactive() -> Color {
+    Color::rgb(0x2B, 0x3A, 0x67)
+}
+
+pub const fn interactive_muted() -> Color {
+    Color::rgb(0x3D, 0x4B, 0x72)
+}

lib/ruin_app/src/text_style.rs

@@ -0,0 +1,61 @@
+use std::cell::RefCell;
+
+use ruin_ui::{Color, TextFontFamily, TextWrap};
+
+use crate::primitives::FontWeight;
+
+/// Partially-specified text style for context-based inheritance.
+///
+/// Set on a container via `.text_style(...)`. All descendant `text()` nodes inherit
+/// any fields that are `Some`, falling back to their own defaults for fields that are `None`.
+/// Inner (closer) ancestors take precedence over outer ancestors.
+#[derive(Clone, Default)]
+pub struct PartialTextStyle {
+    pub size: Option<f32>,
+    pub color: Option<Color>,
+    pub weight: Option<FontWeight>,
+    pub font_family: Option<TextFontFamily>,
+    pub wrap: Option<TextWrap>,
+    pub line_height: Option<f32>,
+}
+
+impl PartialTextStyle {
+    /// Merge `other` on top of `self` — `other`'s `Some` fields win.
+    fn merge_over(self, other: &PartialTextStyle) -> Self {
+        Self {
+            size: other.size.or(self.size),
+            color: other.color.or(self.color),
+            weight: other.weight.or(self.weight),
+            font_family: other.font_family.clone().or(self.font_family),
+            wrap: other.wrap.or(self.wrap),
+            line_height: other.line_height.or(self.line_height),
+        }
+    }
+}
+
+thread_local! {
+    static TEXT_STYLE_STACK: RefCell<Vec<PartialTextStyle>> = const { RefCell::new(Vec::new()) };
+}
+
+/// Push a partial style onto the context stack. Must be paired with `pop_text_style`.
+pub(crate) fn push_text_style(style: PartialTextStyle) {
+    TEXT_STYLE_STACK.with(|stack| stack.borrow_mut().push(style));
+}
+
+/// Pop the top partial style from the context stack.
+pub(crate) fn pop_text_style() {
+    TEXT_STYLE_STACK.with(|stack| {
+        stack.borrow_mut().pop();
+    });
+}
+
+/// Returns the effective `PartialTextStyle` at the current render position by merging
+/// all layers from outermost to innermost (innermost wins).
+pub(crate) fn current_text_style() -> PartialTextStyle {
+    TEXT_STYLE_STACK.with(|stack| {
+        stack
+            .borrow()
+            .iter()
+            .fold(PartialTextStyle::default(), |acc, layer| acc.merge_over(layer))
+    })
+}

lib/ruin_app/src/view.rs

@@ -0,0 +1,239 @@
+use ruin_ui::Element;
+
+use crate::Component;
+use crate::input::EventBindings;
+
+#[derive(Clone, Default)]
+pub struct View {
+    pub(crate) element: Element,
+    pub(crate) bindings: EventBindings,
+}
+
+impl View {
+    pub fn from_element(element: Element) -> Self {
+        Self {
+            element,
+            bindings: EventBindings::default(),
+        }
+    }
+
+    pub fn element(&self) -> &Element {
+        &self.element
+    }
+
+    pub fn from_container(element: Element, children: Vec<View>) -> Self {
+        let mut composed = Self::from_element(element);
+        let mut element = composed.element;
+
+        for child in children {
+            element = element.child(child.element);
+            composed.bindings.extend(child.bindings);
+        }
+
+        composed.element = element;
+        composed
+    }
+}
+
+impl From<Element> for View {
+    fn from(element: Element) -> Self {
+        Self::from_element(element)
+    }
+}
+
+pub trait IntoView {
+    fn into_view(self) -> View;
+}
+
+impl IntoView for View {
+    fn into_view(self) -> View {
+        self
+    }
+}
+
+impl IntoView for Element {
+    fn into_view(self) -> View {
+        View::from_element(self)
+    }
+}
+
+impl<T: Component> IntoView for T {
+    fn into_view(self) -> View {
+        self.render()
+    }
+}
+
+pub trait Children {
+    fn into_views(self) -> Vec<View>;
+}
+
+#[derive(Clone, Default)]
+pub struct ChildViews(pub(crate) Vec<View>);
+
+impl ChildViews {
+    pub fn from_children(children: impl Children) -> Self {
+        Self(children.into_views())
+    }
+
+    pub fn into_vec(self) -> Vec<View> {
+        self.0
+    }
+}
+
+impl Children for () {
+    fn into_views(self) -> Vec<View> {
+        Vec::new()
+    }
+}
+
+
+impl<T: IntoView> Children for T {
+    fn into_views(self) -> Vec<View> {
+        vec![self.into_view()]
+    }
+}
+
+impl<T: IntoView> Children for Vec<T> {
+    fn into_views(self) -> Vec<View> {
+        self.into_iter().map(IntoView::into_view).collect()
+    }
+}
+
+impl Children for ChildViews {
+    fn into_views(self) -> Vec<View> {
+        self.0
+    }
+}
+
+/// Wraps a lazy closure so it can be used as container children.
+///
+/// The closure is called exactly once, inside the builder's `.children()` method,
+/// after any `PartialTextStyle` context has been pushed. This enables text style
+/// inheritance from ancestor containers.
+///
+/// The `view!` macro automatically generates `LazyChildren(|| vec![...])` for
+/// primitive container nodes so that style context propagates correctly.
+pub struct LazyChildren<F: FnOnce() -> Vec<View>>(pub F);
+
+impl<F: FnOnce() -> Vec<View>> Children for LazyChildren<F> {
+    fn into_views(self) -> Vec<View> {
+        (self.0)()
+    }
+}
+
+macro_rules! impl_children_tuple {
+    ($($name:ident),+ $(,)?) => {
+        #[allow(non_camel_case_types)]
+        impl<$($name: IntoView),+> Children for ($($name,)+) {
+            fn into_views(self) -> Vec<View> {
+                let ($($name,)+) = self;
+                vec![$($name.into_view(),)+]
+            }
+        }
+    };
+}
+
+impl_children_tuple!(a, b);
+impl_children_tuple!(a, b, c);
+impl_children_tuple!(a, b, c, d);
+impl_children_tuple!(a, b, c, d, e);
+impl_children_tuple!(a, b, c, d, e, f);
+impl_children_tuple!(a, b, c, d, e, f, g);
+impl_children_tuple!(a, b, c, d, e, f, g, h);
+
+pub trait TextChildren {
+    fn into_text(self) -> String;
+}
+
+#[derive(Clone, Debug, Default, PartialEq, Eq)]
+pub struct TextValue(pub(crate) String);
+
+impl TextValue {
+    pub fn from_text(children: impl TextChildren) -> Self {
+        Self(children.into_text())
+    }
+
+    pub fn into_string(self) -> String {
+        self.0
+    }
+}
+
+impl TextChildren for TextValue {
+    fn into_text(self) -> String {
+        self.0
+    }
+}
+
+impl TextChildren for &'static str {
+    fn into_text(self) -> String {
+        self.to_string()
+    }
+}
+
+impl TextChildren for String {
+    fn into_text(self) -> String {
+        self
+    }
+}
+
+impl TextChildren for i32 {
+    fn into_text(self) -> String {
+        self.to_string()
+    }
+}
+
+impl TextChildren for i64 {
+    fn into_text(self) -> String {
+        self.to_string()
+    }
+}
+
+impl TextChildren for usize {
+    fn into_text(self) -> String {
+        self.to_string()
+    }
+}
+
+impl TextChildren for u64 {
+    fn into_text(self) -> String {
+        self.to_string()
+    }
+}
+
+impl TextChildren for f32 {
+    fn into_text(self) -> String {
+        self.to_string()
+    }
+}
+
+impl<T: std::fmt::Display + 'static> TextChildren for crate::hooks::Signal<T> {
+    fn into_text(self) -> String {
+        self.with(|value| value.to_string())
+    }
+}
+
+impl<T: std::fmt::Display + 'static> TextChildren for crate::hooks::Memo<T> {
+    fn into_text(self) -> String {
+        self.with(|value| value.to_string())
+    }
+}
+
+macro_rules! impl_text_children_tuple {
+    ($($name:ident),+ $(,)?) => {
+        #[allow(non_camel_case_types)]
+        impl<$($name: TextChildren),+> TextChildren for ($($name,)+) {
+            fn into_text(self) -> String {
+                let ($($name,)+) = self;
+                let mut text = String::new();
+                $(text.push_str(&$name.into_text());)+
+                text
+            }
+        }
+    };
+}
+
+impl_text_children_tuple!(a, b);
+impl_text_children_tuple!(a, b, c);
+impl_text_children_tuple!(a, b, c, d);
+impl_text_children_tuple!(a, b, c, d, e);
+impl_text_children_tuple!(a, b, c, d, e, f);

lib/ruin_app_proc_macros/src/lib.rs

@@ -686,22 +686,48 @@ fn expand_node(node: &Node) -> proc_macro2::TokenStream {
         let value = &property.value;
         quote! { .#name(#value) }
     });
-    let children = expand_children(&node.children);
 
     if is_component_path(path) {
+        // Component nodes: eager children so #[component] builder impls keep working.
+        let children = expand_children(&node.children);
         quote! {
             #path::builder()
                 #(#prop_calls)*
                 .children(#children)
         }
-    } else {
+    } else if is_text_path(path) {
+        // text(): children are TextChildren (string/value), not Views — keep eager.
+        let children = expand_children(&node.children);
         quote! {
             ::ruin_app::#path()
                 #(#prop_calls)*
                 .children(#children)
         }
+    } else {
+        // Primitive container nodes (column, row, block, button, scroll_box, …):
+        // Wrap children in a LazyChildren closure so that PartialTextStyle context is
+        // pushed BEFORE children run, enabling correct text style inheritance.
+        //
+        // Each child is spread via Children::into_views(), which handles:
+        //   - Child::Node results (View) via impl<T: IntoView> Children for T
+        //   - &str literals via Children for &str
+        //   - ChildViews (slot values) via Children for ChildViews (flattens)
+        let items = node.children.iter().map(expand_child);
+        quote! {
+            ::ruin_app::#path()
+                #(#prop_calls)*
+                .children(::ruin_app::LazyChildren(|| {
+                    let mut __v: ::std::vec::Vec<::ruin_app::View> = ::std::vec::Vec::new();
+                    #(__v.extend(::ruin_app::Children::into_views(#items));)*
+                    __v
+                }))
         }
     }
+}
+
+fn is_text_path(path: &Path) -> bool {
+    path.segments.len() == 1 && path.segments[0].ident == "text"
+}
 
 fn expand_provider_node(node: &Node) -> proc_macro2::TokenStream {
     let path = &node.path;

lib/runtime/README.md

@@ -0,0 +1,4 @@
+# RUIN - Runtime
+
+The RUIN runtime is an event-loop-per-thread, non-workstealing async executor implemented on top of Linux io_uring
+with 

lib/runtime/src/fs.rs

@@ -8,11 +8,12 @@
 //! The public surface intentionally mirrors `std::fs` where that shape makes sense, while using
 //! async methods for operations that may block the caller.
 
+use alloc::sync::Arc;
+
 use std::ffi::OsStr;
 use std::io;
 use std::os::fd::{AsRawFd, OwnedFd};
 use std::path::{Path, PathBuf};
-use std::sync::Arc;
 
 use crate::op::fs::{
     FileType as RawFileType, FsOp, MetadataTarget, OpenOptions as OpOpenOptions,

lib/runtime/src/lib.rs

@@ -29,7 +29,10 @@ pub(crate) mod trace_targets {
     pub const DRIVER: &str = "ruin_runtime::driver";
     pub const RUNTIME: &str = "ruin_runtime::runtime";
     pub const SCHEDULER: &str = "ruin_runtime::scheduler";
+
+    #[cfg(debug_assertions)]
     pub const TIMER: &str = "ruin_runtime::timer";
+    #[cfg(debug_assertions)]
     pub const ASYNC: &str = "ruin_runtime::async";
 }
 
@@ -41,6 +44,7 @@ pub mod net;
 pub mod op;
 #[doc(hidden)]
 pub mod platform;
+pub mod stdio;
 #[doc(hidden)]
 pub mod sys;
 pub mod time;

lib/runtime/src/net.rs

@@ -3,14 +3,15 @@
 //! The public surface follows the general shape of `std::net`, but uses async methods for socket
 //! operations that would otherwise block the caller.
 
-use std::future::Future;
+use core::future::Future;
+use core::pin::Pin;
+use core::task::{Context, Poll};
+use core::time::Duration;
+
 use std::io;
 use std::net::{Shutdown, SocketAddr, ToSocketAddrs};
 use std::os::fd::{AsRawFd, FromRawFd, OwnedFd, RawFd};
-use std::pin::Pin;
 use std::sync::{Arc, Mutex};
-use std::task::{Context, Poll};
-use std::time::Duration;
 
 use hyper::rt::{Read as HyperRead, ReadBufCursor, Write as HyperWrite};
 

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

@@ -1,4 +1,6 @@
-//! Public runtime driver primitives.
+//! RUIN Runtime Driver for Linux x86_64.
+//! 
+//! 
 
 use std::cell::Cell;
 use std::cell::RefCell;
@@ -88,12 +90,21 @@ pub struct ReadyEvents {
 
 /// Low-level Linux runtime driver backed by `io_uring`.
 pub struct Driver {
+    /// The `io_uring` instance driving this runtime thread.
     ring: IoUring,
+    /// Shared notifier that other threads can use to wake this runtime thread.
     notifier: Arc<NotifierInner>,
+    /// Next sequence number for generated completion tokens.
     next_token: Cell<u64>,
+    /// The token of the currently active timer, if any timer is armed.
     active_timer_token: Cell<Option<u64>>,
+    /// Accumulated count of pending wake notifications that have not yet been triggered.
     pending_wakes: Cell<u64>,
+    /// Accumulated count of pending timer expirations that have not yet been triggered.
     pending_timers: Cell<u64>,
+    /// Map of active completion tokens to associated handlers. When a CQE is received with a token in this map, the
+    /// corresponding handler will be invoked with the CQE and removed from the map. This is the core mechanism by which
+    /// async operations are tracked and dispatched to their continuations.
     completions: RefCell<HashMap<u64, CompletionHandler>>,
 }
 

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

@@ -54,6 +54,12 @@ pub struct TimeoutHandle {
     _local: Rc<()>,
 }
 
+impl TimeoutHandle {
+    pub fn clear(&self) {
+        clear_timeout(self);
+    }
+}
+
 #[derive(Clone)]
 /// Handle returned by [`set_interval`].
 pub struct IntervalHandle {
@@ -62,6 +68,12 @@ pub struct IntervalHandle {
     _local: Rc<()>,
 }
 
+impl IntervalHandle {
+    pub fn clear(&self) {
+        clear_interval(self);
+    }
+}
+
 /// Handle returned by [`queue_future`].
 ///
 /// Awaiting a join handle yields the output of the queued future.
@@ -72,9 +84,10 @@ pub struct JoinHandle<T> {
 /// Future returned by [`yield_now`].
 ///
 /// Awaiting this future will immediately yield control back to the runtime scheduler, allowing other queued microtasks
-/// to run before the current task continues executing. Note that continuation of futures runs as a microtask, so this
+/// to run before the current task continues executing. Note that continuations of futures run as microtasks, so this
 /// can only yield to other microtasks and not to macrotasks (driver events such as file or network I/O, timers, or
-/// channel messages).
+/// channel messages). To yield to macrotasks, you must allow the flow of execution to return to the runtime event loop
+/// and flush the full microtask queue, for example by awaiting a timer.
 pub struct YieldNow {
     yielded: bool,
 }
@@ -217,17 +230,19 @@ where
     );
 
     if delay.is_zero() {
+        unimplemented!("Zero-delay intervals are not yet implemented.")
+        // TODO: vibeshit got this completely wrong
         // Zero-delay intervals never touch the timer heap or arm an io_uring
         // timer (a past-deadline kernel timer would fire on every event loop
         // iteration, spinning the runtime at 100 % CPU).  Instead the callback
         // is stored in `immediate_intervals` and self-schedules as a macrotask
         // each turn, mirroring JS `setInterval(f, 0)` semantics.
-        let callback = Rc::new(RefCell::new(Box::new(callback) as Box<dyn FnMut()>));
-        current_thread()
-            .immediate_intervals
-            .borrow_mut()
-            .insert(id, Rc::clone(&callback));
-        schedule_immediate_interval(owner, id);
+        // let callback = Rc::new(RefCell::new(Box::new(callback) as Box<dyn FnMut()>));
+        // current_thread()
+        //     .immediate_intervals
+        //     .borrow_mut()
+        //     .insert(id, Rc::clone(&callback));
+        // schedule_immediate_interval(owner, id);
     } else {
         let deadline = deadline_from_now(delay);
         #[cfg(debug_assertions)]
@@ -571,6 +586,8 @@ impl Future for YieldNow {
     }
 }
 
+type ImmediateIntervals = RefCell<HashMap<usize, Rc<RefCell<Box<dyn FnMut()>>>>>;
+
 struct ThreadState {
     driver: Driver,
     shared: Arc<ThreadShared>,
@@ -580,7 +597,7 @@ struct ThreadState {
     timers: RefCell<TimerHeap>,
     /// Zero-delay intervals bypasses the timer heap entirely. Each entry
     /// re-enqueues itself as a macrotask on every turn.
-    immediate_intervals: RefCell<HashMap<usize, Rc<RefCell<Box<dyn FnMut()>>>>>,
+    immediate_intervals: ImmediateIntervals,
     next_timer_id: Cell<usize>,
     children: RefCell<Vec<ChildWorker>>,
 }
@@ -1162,27 +1179,32 @@ fn clear_timer(owner: *const ThreadState, id: usize) {
     }
 }
 
-/// Enqueues one macrotask turn for a zero-delay interval.
-///
-/// The macrotask checks whether the interval is still live (not cleared), fires
-/// the callback, and re-enqueues itself for the next turn.
-fn schedule_immediate_interval(owner: *const ThreadState, id: usize) {
-    push_local_macrotask(Box::new(move || {
-        let callback = current_thread()
-            .immediate_intervals
-            .borrow()
-            .get(&id)
-            .map(Rc::clone);
-        let Some(callback) = callback else {
-            return; // interval was cleared before this turn ran
-        };
-        (callback.borrow_mut())();
-        // Re-enqueue for the next turn if still live.
-        if current_thread().immediate_intervals.borrow().contains_key(&id) {
-            schedule_immediate_interval(owner, id);
-        }
-    }));
-}
+// TODO: vibeshit got this completely wrong
+// /// Enqueues one macrotask turn for a zero-delay interval.
+// ///
+// /// The macrotask checks whether the interval is still live (not cleared), fires
+// /// the callback, and re-enqueues itself for the next turn.
+// fn schedule_immediate_interval(owner: *const ThreadState, id: usize) {
+//     push_local_macrotask(Box::new(move || {
+//         let callback = current_thread()
+//             .immediate_intervals
+//             .borrow()
+//             .get(&id)
+//             .map(Rc::clone);
+//         let Some(callback) = callback else {
+//             return; // interval was cleared before this turn ran
+//         };
+//         (callback.borrow_mut())();
+//         // Re-enqueue for the next turn if still live.
+//         if current_thread()
+//             .immediate_intervals
+//             .borrow()
+//             .contains_key(&id)
+//         {
+//             schedule_immediate_interval(owner, id);
+//         }
+//     }));
+// }
 
 fn dispatch_expired_timers() {
     let now = deadline_from_now(Duration::ZERO);
@@ -1207,12 +1229,8 @@ fn dispatch_expired_timers() {
                     .deadline
                     .checked_add(interval)
                     .unwrap_or(Duration::MAX);
-                let next_timer = TimerNode::interval(
-                    timer.id,
-                    next_deadline,
-                    interval,
-                    Rc::clone(&callback),
-                );
+                let next_timer =
+                    TimerNode::interval(timer.id, next_deadline, interval, Rc::clone(&callback));
                 current_thread().timers.borrow_mut().insert(next_timer);
 
                 push_local_macrotask(Box::new(move || {
@@ -1394,8 +1412,7 @@ mod tests {
         // turns by awaiting a sleep between checks.
         let count = Rc::new(Cell::new(0usize));
         let count_clone = Rc::clone(&count);
-        let handle_slot: Rc<RefCell<Option<super::IntervalHandle>>> =
-            Rc::new(RefCell::new(None));
+        let handle_slot: Rc<RefCell<Option<super::IntervalHandle>>> = Rc::new(RefCell::new(None));
         let handle_slot_clone = Rc::clone(&handle_slot);
 
         let handle = set_interval(Duration::ZERO, move || {

lib/runtime/src/stdio.rs

@@ -0,0 +1,191 @@
+//! 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;
+use crate::platform::linux_x86_64::runtime::with_current_driver;
+use crate::platform::linux_x86_64::uring::{IORING_OP_READ, IoUringCqe, IoUringSqe};
+
+thread_local! {
+    static STDIN_URING_SUPPORTED: Cell<Option<bool>> = const { Cell::new(None) };
+}
+
+const FILE_CURSOR: u64 = u64::MAX;
+const READ_CHUNK_BYTES: usize = 1024;
+
+/// Async line-oriented stdin reader.
+///
+/// The reader is `io_uring`-first. When the active stdin fd rejects `IORING_OP_READ`, the module
+/// falls back to a helper-thread blocking read on the same duplicated fd.
+pub struct Stdin {
+    fd: OwnedFd,
+    buffer: Vec<u8>,
+}
+
+/// Opens an async stdin reader.
+pub fn stdin() -> io::Result<Stdin> {
+    let raw = cvt(unsafe { libc::fcntl(libc::STDIN_FILENO, libc::F_DUPFD_CLOEXEC, 0) })?;
+    Ok(Stdin {
+        fd: unsafe { OwnedFd::from_raw_fd(raw) },
+        buffer: Vec::new(),
+    })
+}
+
+impl Stdin {
+    /// Reads a single UTF-8 line, including the trailing newline when present.
+    ///
+    /// Returns `Ok(None)` on EOF.
+    pub async fn read_line(&mut self) -> io::Result<Option<String>> {
+        loop {
+            if let Some(index) = self.buffer.iter().position(|byte| *byte == b'\n') {
+                let line = self.buffer.drain(..=index).collect::<Vec<_>>();
+                return decode_line(line).map(Some);
+            }
+
+            let chunk = self.read_chunk().await?;
+            if chunk.is_empty() {
+                if self.buffer.is_empty() {
+                    return Ok(None);
+                }
+                let line = std::mem::take(&mut self.buffer);
+                return decode_line(line).map(Some);
+            }
+
+            self.buffer.extend_from_slice(&chunk);
+        }
+    }
+
+    async fn read_chunk(&self) -> io::Result<Vec<u8>> {
+        let fd = self.fd.as_raw_fd();
+        let support = STDIN_URING_SUPPORTED.with(Cell::get);
+        if support != Some(false) {
+            match submit_uring_read(fd, READ_CHUNK_BYTES).await {
+                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),
+            }
+        }
+
+        offload(move || {
+            let mut buffer = vec![0; READ_CHUNK_BYTES];
+            let read = blocking_read(fd, &mut buffer)?;
+            if read == 0 {
+                buffer.clear();
+            } else {
+                buffer.truncate(read);
+            }
+            Ok(buffer)
+        })
+        .await
+    }
+}
+
+async fn offload<T: Send + 'static>(
+    task: impl FnOnce() -> io::Result<T> + Send + 'static,
+) -> io::Result<T> {
+    let (future, handle) = completion_for_current_thread::<io::Result<T>>();
+    thread::Builder::new()
+        .name("ruin-runtime-stdio-offload".into())
+        .spawn(move || handle.complete(task()))
+        .map_err(io::Error::other)?;
+    future.await
+}
+
+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();
+    let capacity = buffer.len();
+    submit_uring(
+        move |sqe| {
+            sqe.opcode = IORING_OP_READ;
+            sqe.fd = fd;
+            sqe.addr = ptr as u64;
+            sqe.len = capacity as u32;
+            sqe.off = FILE_CURSOR;
+        },
+        move |cqe| {
+            let read = cqe_to_result(cqe)? as usize;
+            buffer.truncate(read);
+            Ok(buffer)
+        },
+    )
+    .await
+}
+
+async fn submit_uring<T: Send + 'static, M>(
+    fill: impl FnOnce(&mut IoUringSqe),
+    map: M,
+) -> io::Result<T>
+where
+    M: FnOnce(IoUringCqe) -> io::Result<T> + Send + 'static,
+{
+    let (future, handle) = completion_for_current_thread::<io::Result<T>>();
+    let callback_handle = handle.clone();
+    let token = with_current_driver(|driver| {
+        driver.submit_operation(fill, move |cqe| {
+            callback_handle.complete(map(cqe));
+        })
+    })?;
+
+    handle.set_cancel(move || {
+        let _ = with_current_driver(|driver| driver.cancel_operation(token));
+    });
+
+    future.await
+}
+
+fn blocking_read(fd: RawFd, buffer: &mut [u8]) -> io::Result<usize> {
+    loop {
+        let read = unsafe {
+            libc::read(
+                fd,
+                buffer.as_mut_ptr().cast::<libc::c_void>(),
+                buffer.len(),
+            )
+        };
+        if read >= 0 {
+            return Ok(read as usize);
+        }
+
+        let error = io::Error::last_os_error();
+        if error.kind() == io::ErrorKind::Interrupted {
+            continue;
+        }
+        return Err(error);
+    }
+}
+
+fn decode_line(bytes: Vec<u8>) -> io::Result<String> {
+    String::from_utf8(bytes).map_err(|error| io::Error::new(io::ErrorKind::InvalidData, error))
+}
+
+fn cqe_to_result(cqe: IoUringCqe) -> io::Result<i32> {
+    if cqe.res < 0 {
+        Err(io::Error::from_raw_os_error(-cqe.res))
+    } else {
+        Ok(cqe.res)
+    }
+}
+
+fn should_fallback_to_offload(error: &io::Error) -> bool {
+    matches!(
+        error.raw_os_error(),
+        Some(libc::EINVAL | libc::ENOSYS | libc::EOPNOTSUPP)
+    )
+}
+
+fn cvt(value: libc::c_int) -> io::Result<libc::c_int> {
+    if value == -1 {
+        Err(io::Error::last_os_error())
+    } else {
+        Ok(value)
+    }
+}

lib/runtime/src/time.rs

@@ -3,14 +3,14 @@
 //! These helpers integrate with the runtime's timer queue and are designed to be used from
 //! futures scheduled with [`crate::queue_future`] or one of the runtime entry macros.
 
-use std::cell::{Cell, RefCell};
-use std::fmt;
-use std::future::{Future, poll_fn};
-use std::pin::Pin;
-use std::rc::Rc;
-use std::task::Waker;
-use std::task::{Context, Poll};
-use std::time::Duration;
+use alloc::rc::Rc;
+use core::cell::{Cell, RefCell};
+use core::fmt;
+use core::future::{Future, poll_fn};
+use core::pin::Pin;
+use core::task::Waker;
+use core::task::{Context, Poll};
+use core::time::Duration;
 
 use crate::{clear_timeout, set_timeout};
 

lib/ui/src/interaction.rs

@@ -54,7 +54,7 @@ pub struct RoutedPointerEvent {
 #[derive(Default)]
 pub struct PointerRouter {
     hovered: Vec<HitTarget>,
-    pressed: Option<HitTarget>,
+    pressed: Option<Vec<HitTarget>>,
 }
 
 impl PointerRouter {
@@ -71,7 +71,11 @@ impl PointerRouter {
     }
 
     pub fn pressed_target(&self) -> Option<&HitTarget> {
-        self.pressed.as_ref()
+        self.pressed.as_ref().and_then(|targets| targets.last())
+    }
+
+    pub fn pressed_targets(&self) -> &[HitTarget] {
+        self.pressed.as_deref().unwrap_or(&[])
     }
 
     pub fn route(
@@ -114,7 +118,12 @@ impl PointerRouter {
 
         match event.kind {
             PointerEventKind::Move => {
-                if let Some(target) = self.pressed.clone().or(hit_target.clone()) {
+                if let Some(target) = self
+                    .pressed
+                    .as_ref()
+                    .and_then(|targets| targets.last().cloned())
+                    .or(hit_target.clone())
+                {
                     routed.push(RoutedPointerEvent {
                         kind: RoutedPointerEventKind::Move,
                         target,
@@ -125,7 +134,7 @@ impl PointerRouter {
             }
             PointerEventKind::Down { button } => {
                 if let Some(target) = hit_target {
-                    self.pressed = Some(target.clone());
+                    self.pressed = Some(self.hovered.clone());
                     routed.push(RoutedPointerEvent {
                         kind: RoutedPointerEventKind::Down { button },
                         target,
@@ -135,7 +144,12 @@ impl PointerRouter {
                 }
             }
             PointerEventKind::Up { button } => {
-                if let Some(target) = self.pressed.take().or(hit_target) {
+                if let Some(target) = self
+                    .pressed
+                    .take()
+                    .and_then(|targets| targets.last().cloned())
+                    .or(hit_target)
+                {
                     routed.push(RoutedPointerEvent {
                         kind: RoutedPointerEventKind::Up { button },
                         target,

lib/ui/src/layout.rs

@@ -7,7 +7,7 @@ use crate::scene::{
     UiSize,
 };
 use crate::text::TextSystem;
-use crate::tree::{CursorIcon, Edges, Element, ElementId, FlexDirection, ImageNode, Style};
+use crate::tree::{AlignItems, CursorIcon, Edges, Element, ElementId, FlexDirection, ImageNode, Style};
 
 pub fn layout_scene(version: u64, logical_size: UiSize, root: &Element) -> SceneSnapshot {
     let mut text_system = TextSystem::new();
@@ -27,6 +27,11 @@ pub fn layout_scene_with_text_system(
 pub struct LayoutSnapshot {
     pub scene: SceneSnapshot,
     pub interaction_tree: InteractionTree,
+    /// Minimum size the root element needs in logical units.  Accounts for
+    /// `min_width`/`min_height` constraints and the natural minimum of fixed-
+    /// size content.  Scroll boxes contribute only their own explicit/min size
+    /// on the scroll axis, not their content.
+    pub root_min_size: UiSize,
 }
 
 #[derive(Clone, Debug, Eq, Hash, PartialEq)]
@@ -128,7 +133,12 @@ impl LayoutNode {
     /// Return a copy of this node (and all descendants) with all positions shifted by `offset`.
     pub fn translated(self, offset: Point) -> Self {
         fn translate_rect(r: Rect, o: Point) -> Rect {
-            Rect::new(r.origin.x + o.x, r.origin.y + o.y, r.size.width, r.size.height)
+            Rect::new(
+                r.origin.x + o.x,
+                r.origin.y + o.y,
+                r.size.width,
+                r.size.height,
+            )
         }
         let rect = translate_rect(self.rect, offset);
         let clip_rect = self.clip_rect.map(|r| translate_rect(r, offset));
@@ -143,7 +153,11 @@ impl LayoutNode {
             rect: translate_rect(img.rect, offset),
             ..img
         });
-        let children = self.children.into_iter().map(|c| c.translated(offset)).collect();
+        let children = self
+            .children
+            .into_iter()
+            .map(|c| c.translated(offset))
+            .collect();
         LayoutNode {
             rect,
             clip_rect,
@@ -233,14 +247,17 @@ pub fn layout_snapshot_with_cache(
             "layout snapshot perf"
         );
     }
+    let root_min_size = element_min_size(root);
     LayoutSnapshot {
         scene,
         interaction_tree: InteractionTree {
             root: interaction_root,
         },
+        root_min_size,
     }
 }
 
+#[allow(clippy::too_many_arguments)]
 fn layout_element(
     element: &Element,
     rect: Rect,
@@ -254,10 +271,12 @@ fn layout_element(
     clip_rect: Option<Rect>,
 ) -> LayoutNode {
     perf_stats.nodes += 1;
+    let rect = snap_rect(rect);
 
     // Viewport culling: skip fully off-screen elements inside a scroll box.
-    if let Some(clip) = clip_rect {
-        if !rects_overlap(rect, clip) {
+    if let Some(clip) = clip_rect
+        && !rects_overlap(rect, clip)
+    {
         perf_stats.viewport_culled += 1;
         return LayoutNode {
             path,
@@ -274,7 +293,6 @@ fn layout_element(
             children: Vec::new(),
         };
     }
-    }
 
     // Incremental layout cache check.
     // Round to nearest pixel to eliminate floating-point representation
@@ -368,7 +386,13 @@ fn layout_element(
         if pushed_clip {
             scene.pop_clip();
         }
-        cache_layout(layout_cache, cache_key, &interaction, &scene.items[scene_start..], rect.origin);
+        cache_layout(
+            layout_cache,
+            cache_key,
+            &interaction,
+            &scene.items[scene_start..],
+            rect.origin,
+        );
         return interaction;
     }
 
@@ -382,7 +406,13 @@ fn layout_element(
         if pushed_clip {
             scene.pop_clip();
         }
-        cache_layout(layout_cache, cache_key, &interaction, &scene.items[scene_start..], rect.origin);
+        cache_layout(
+            layout_cache,
+            cache_key,
+            &interaction,
+            &scene.items[scene_start..],
+            rect.origin,
+        );
         return interaction;
     }
 
@@ -508,7 +538,13 @@ fn layout_element(
         if pushed_clip {
             scene.pop_clip();
         }
-        cache_layout(layout_cache, cache_key, &interaction, &scene.items[scene_start..], rect.origin);
+        cache_layout(
+            layout_cache,
+            cache_key,
+            &interaction,
+            &scene.items[scene_start..],
+            rect.origin,
+        );
         return interaction;
     }
 
@@ -518,7 +554,13 @@ fn layout_element(
         if pushed_clip {
             scene.pop_clip();
         }
-        cache_layout(layout_cache, cache_key, &interaction, &scene.items[scene_start..], rect.origin);
+        cache_layout(
+            layout_cache,
+            cache_key,
+            &interaction,
+            &scene.items[scene_start..],
+            rect.origin,
+        );
         return interaction;
     }
 
@@ -527,7 +569,13 @@ fn layout_element(
         if pushed_clip {
             scene.pop_clip();
         }
-        cache_layout(layout_cache, cache_key, &interaction, &scene.items[scene_start..], rect.origin);
+        cache_layout(
+            layout_cache,
+            cache_key,
+            &interaction,
+            &scene.items[scene_start..],
+            rect.origin,
+        );
         return interaction;
     }
     interaction.children = layout_container_children(
@@ -538,14 +586,26 @@ fn layout_element(
         text_system,
         perf_stats,
         layout_cache,
-        clip_rect,
+        // Do NOT propagate clip_rect into children: the scroll-box PushClip already clips
+        // 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 {
         scene.pop_clip();
     }
 
-    cache_layout(layout_cache, cache_key, &interaction, &scene.items[scene_start..], rect.origin);
+    cache_layout(
+        layout_cache,
+        cache_key,
+        &interaction,
+        &scene.items[scene_start..],
+        rect.origin,
+    );
     interaction
 }
 
@@ -558,10 +618,13 @@ fn cache_layout(
     origin: Point,
 ) {
     let neg = Point::new(-origin.x, -origin.y);
-    cache.results.insert(key, CachedLayout {
+    cache.results.insert(
+        key,
+        CachedLayout {
             interaction_node: interaction.clone().translated(neg),
             scene_items: scene_items.iter().map(|i| i.translated(neg)).collect(),
-    });
+        },
+    );
 }
 
 fn hit_path_node(node: &LayoutNode, point: crate::scene::Point) -> Option<Vec<HitTarget>> {
@@ -730,11 +793,16 @@ fn point_in_rounded_rect(point: crate::scene::Point, rect: Rect, radius: f32) ->
 
 #[derive(Clone, Copy, Debug)]
 struct MeasuredChild {
+    /// Offered cross-axis size (full available_cross for stretch; explicit value otherwise).
     cross: f32,
+    /// Natural cross-axis size: set when parent uses non-stretch alignment, child has no
+    /// explicit cross size, and the child is not flex. `None` means use `cross`.
+    natural_cross: Option<f32>,
     main: f32,
     is_flex: bool,
 }
 
+#[allow(clippy::too_many_arguments)]
 fn layout_container_children(
     element: &Element,
     content: Rect,
@@ -759,15 +827,29 @@ fn layout_container_children(
     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);
+        // min-size constraints (content-box) converted to outer.
+        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);
+        // style.width/height are content-box; add insets to get the outer (allocated) size.
+        // min-cross acts as floor; allow exceeding available_cross only when min demands it.
         let cross = child_cross_size(child, element.style.direction)
-            .unwrap_or(available_cross)
-            .clamp(0.0, available_cross);
-        let explicit_main =
-            child_main_size(child, element.style.direction).map(|main| main.max(0.0));
+            .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 {
-                0.0
+                // Flex items get their share of remaining space later; record min floor now.
+                min_main_outer
             } else {
                 perf_stats.intrinsic_calls += 1;
                 if child.text_node().is_some() {
@@ -788,9 +870,35 @@ fn layout_container_children(
                 if let Some(intrinsic_started) = intrinsic_started {
                     perf_stats.intrinsic_ms += intrinsic_started.elapsed().as_secs_f64() * 1_000.0;
                 }
-                intrinsic
+                // Apply min-main floor to intrinsic result.
+                intrinsic.max(min_main_outer)
             }
         });
+        // For non-stretch alignment, measure the child's natural cross size so it is not
+        // forcibly stretched to fill the container's cross axis. Only done for non-flex
+        // 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 =
+            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 {
@@ -798,6 +906,7 @@ fn layout_container_children(
         }
         measured_children.push(MeasuredChild {
             cross,
+            natural_cross,
             main: measured_main,
             is_flex,
         });
@@ -808,20 +917,39 @@ fn layout_container_children(
     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 {
-            if flex_total <= 0.0 {
+            let allocated = if flex_total <= 0.0 {
                 0.0
             } else {
                 remaining_main * (child_flex_weight(child) / flex_total)
-            }
+            };
+            // Apply min-main floor to flex allocation.
+            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
         };
+        // For non-stretch alignment, use the child's natural cross size; otherwise stretch.
+        // 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 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(
-            content,
+            cross_origin,
             element.style.direction,
             cursor,
             child_main.max(0.0),
-            measured.cross,
+            actual_cross,
         );
         children.push(layout_element(
             child,
@@ -848,13 +976,22 @@ fn intrinsic_main_size(
     layout_cache: &mut LayoutCache,
 ) -> f32 {
     if let Some(text) = child.text_node() {
+        // cross_size and available_main are outer sizes; subtract insets to get content dimensions
+        // for text measurement so wrapping is constrained to the actual content area.
+        let child_insets = content_insets(&child.style);
         let constraints = match direction {
-            FlexDirection::Row => (Some(available_main.max(0.0)), Some(cross_size.max(0.0))),
-            FlexDirection::Column => (Some(cross_size.max(0.0)), None),
+            FlexDirection::Row => (
+                Some((available_main - main_axis_padding(child_insets, direction)).max(0.0)),
+                Some((cross_size - cross_axis_padding(child_insets, direction)).max(0.0)),
+            ),
+            FlexDirection::Column => (
+                Some((cross_size - cross_axis_padding(child_insets, direction)).max(0.0)),
+                None,
+            ),
         };
         let content =
             text_system.measure_spans(&text.spans, &text.style, constraints.0, constraints.1);
-        let padding = main_axis_padding(content_insets(&child.style), direction);
+        let padding = main_axis_padding(child_insets, direction);
         return main_axis_size(content, direction) + padding;
     }
 
@@ -891,19 +1028,29 @@ fn intrinsic_container_content_size(
             let mut height = gap_total;
             for child in &element.children {
                 let skip_main = child.style.flex_grow > 0.0 && child.style.height.is_none();
+                let child_insets = content_insets(&child.style);
+                // Offer outer size: content-box style.w/h + insets, or parent's content width.
+                let offered_w = child
+                    .style
+                    .width
+                    .map(|w| w + horizontal_insets(child_insets))
+                    .unwrap_or(content_size.width);
+                let offered_h = child
+                    .style
+                    .height
+                    .map(|h| h + vertical_insets(child_insets))
+                    .unwrap_or(content_size.height);
                 let child_size = intrinsic_size(
                     child,
-                    UiSize::new(
-                        child.style.width.unwrap_or(content_size.width),
-                        child.style.height.unwrap_or(content_size.height),
-                    ),
+                    UiSize::new(offered_w, offered_h),
                     text_system,
                     perf_stats,
                     layout_cache,
                 );
-                width = width.max(child.style.width.unwrap_or(child_size.width));
+                // child_size is always outer; accumulate directly.
+                width = width.max(child_size.width);
                 if !skip_main {
-                    height += child.style.height.unwrap_or(child_size.height);
+                    height += child_size.height;
                 }
             }
             UiSize::new(width, height)
@@ -921,17 +1068,26 @@ fn intrinsic_container_content_size(
                     child_main_sizes.push(None);
                     continue;
                 }
+                let child_insets = content_insets(&child.style);
+                let offered_w = child
+                    .style
+                    .width
+                    .map(|w| w + horizontal_insets(child_insets))
+                    .unwrap_or(content_size.width);
+                let offered_h = child
+                    .style
+                    .height
+                    .map(|h| h + vertical_insets(child_insets))
+                    .unwrap_or(content_size.height);
                 let child_size = intrinsic_size(
                     child,
-                    UiSize::new(
-                        child.style.width.unwrap_or(content_size.width),
-                        child.style.height.unwrap_or(content_size.height),
-                    ),
+                    UiSize::new(offered_w, offered_h),
                     text_system,
                     perf_stats,
                     layout_cache,
                 );
-                let child_main = child.style.width.unwrap_or(child_size.width);
+                // child_size.width is outer; use directly as the fixed main contribution.
+                let child_main = child_size.width;
                 fixed_main += child_main;
                 child_main_sizes.push(Some(child_main));
             }
@@ -945,12 +1101,15 @@ fn intrinsic_container_content_size(
                         remaining_main * (child_flex_weight(child) / flex_total)
                     }
                 });
+                let child_insets = content_insets(&child.style);
+                let offered_h = child
+                    .style
+                    .height
+                    .map(|h| h + vertical_insets(child_insets))
+                    .unwrap_or(content_size.height);
                 let child_size = intrinsic_size(
                     child,
-                    UiSize::new(
-                        child_main,
-                        child.style.height.unwrap_or(content_size.height),
-                    ),
+                    UiSize::new(child_main, offered_h),
                     text_system,
                     perf_stats,
                     layout_cache,
@@ -958,7 +1117,7 @@ fn intrinsic_container_content_size(
                 if !skip_main {
                     width += child_main;
                 }
-                height = height.max(child.style.height.unwrap_or(child_size.height));
+                height = height.max(child_size.height);
             }
             UiSize::new(width, height)
         }
@@ -986,7 +1145,14 @@ fn intrinsic_size(
         return cached;
     }
     let insets = content_insets(&element.style);
-    let result = intrinsic_size_inner(element, available_size, insets, text_system, perf_stats, layout_cache);
+    let result = intrinsic_size_inner(
+        element,
+        available_size,
+        insets,
+        text_system,
+        perf_stats,
+        layout_cache,
+    );
     layout_cache.intrinsic_cache.insert(cache_key, result);
     result
 }
@@ -999,30 +1165,51 @@ fn intrinsic_size_inner(
     perf_stats: &mut LayoutPerfStats,
     layout_cache: &mut LayoutCache,
 ) -> UiSize {
+    // style.width/height are content-box (content dimensions).
+    // available_size is the outer size the parent is offering.
+    // All returned sizes are outer (content + insets).
+
+    let min_outer_w = element
+        .style
+        .min_width
+        .map(|mw| mw + horizontal_insets(insets))
+        .unwrap_or(0.0);
+    let min_outer_h = element
+        .style
+        .min_height
+        .map(|mh| mh + vertical_insets(insets))
+        .unwrap_or(0.0);
+
     if let Some(text) = element.text_node() {
+        // Measure at content dimensions: use explicit if set, else available minus insets.
+        let content_w = element
+            .style
+            .width
+            .unwrap_or_else(|| (available_size.width - horizontal_insets(insets)).max(0.0));
+        let content_h = element
+            .style
+            .height
+            .unwrap_or_else(|| (available_size.height - vertical_insets(insets)).max(0.0));
         let measured = text_system.measure_spans(
             &text.spans,
             &text.style,
-            Some(available_size.width.max(0.0)),
-            Some(available_size.height.max(0.0)),
+            Some(content_w.max(0.0)),
+            Some(content_h.max(0.0)),
         );
+        // Return outer: explicit (content) + insets, or measured + insets for auto.
         return UiSize::new(
-            element
-                .style
-                .width
-                .unwrap_or(measured.width + horizontal_insets(insets)),
-            element
-                .style
-                .height
-                .unwrap_or(measured.height + vertical_insets(insets)),
+            (element.style.width.unwrap_or(measured.width) + horizontal_insets(insets))
+                .max(min_outer_w),
+            (element.style.height.unwrap_or(measured.height) + vertical_insets(insets))
+                .max(min_outer_h),
         );
     }
 
     if let Some(image) = element.image_node() {
         let resolved = resolve_image_element_size(element, image.resource.size());
         return UiSize::new(
-            resolved.width + horizontal_insets(insets),
-            resolved.height + vertical_insets(insets),
+            (resolved.width + horizontal_insets(insets)).max(min_outer_w),
+            (resolved.height + vertical_insets(insets)).max(min_outer_h),
         );
     }
 
@@ -1031,10 +1218,13 @@ fn intrinsic_size_inner(
     let scroll_gutter = element
         .scroll_box_node()
         .map_or(0.0, |scroll_box| scroll_box.scrollbar.gutter_width.max(0.0));
-    let content_width =
-        explicit_width.unwrap_or(available_size.width).max(0.0) - horizontal_insets(insets);
-    let content_height =
-        explicit_height.unwrap_or(available_size.height).max(0.0) - vertical_insets(insets);
+    // Content dimensions: explicit = already content; auto = available_outer - insets.
+    let content_width = explicit_width
+        .map(|w| w.max(0.0))
+        .unwrap_or_else(|| (available_size.width - horizontal_insets(insets)).max(0.0));
+    let content_height = explicit_height
+        .map(|h| h.max(0.0))
+        .unwrap_or_else(|| (available_size.height - vertical_insets(insets)).max(0.0));
     let content_size = UiSize::new(
         (content_width - scroll_gutter).max(0.0),
         content_height.max(0.0),
@@ -1042,18 +1232,179 @@ fn intrinsic_size_inner(
 
     if element.children.is_empty() {
         return UiSize::new(
-            explicit_width.unwrap_or(horizontal_insets(insets) + scroll_gutter),
-            explicit_height.unwrap_or(vertical_insets(insets)),
+            (explicit_width
+                .map(|w| w + horizontal_insets(insets) + scroll_gutter)
+                .unwrap_or(horizontal_insets(insets) + scroll_gutter))
+            .max(min_outer_w),
+            (explicit_height
+                .map(|h| h + vertical_insets(insets))
+                .unwrap_or(vertical_insets(insets)))
+            .max(min_outer_h),
         );
     }
 
-    let intrinsic_content =
-        intrinsic_container_content_size(element, content_size, text_system, perf_stats, layout_cache);
+    let intrinsic_content = intrinsic_container_content_size(
+        element,
+        content_size,
+        text_system,
+        perf_stats,
+        layout_cache,
+    );
 
     UiSize::new(
-        explicit_width
-            .unwrap_or(intrinsic_content.width + horizontal_insets(insets) + scroll_gutter),
-        explicit_height.unwrap_or(intrinsic_content.height + vertical_insets(insets)),
+        (explicit_width
+            .map(|w| w + horizontal_insets(insets) + scroll_gutter)
+            .unwrap_or(intrinsic_content.width + horizontal_insets(insets) + scroll_gutter))
+        .max(min_outer_w),
+        (explicit_height
+            .map(|h| h + vertical_insets(insets))
+            .unwrap_or(intrinsic_content.height + vertical_insets(insets)))
+        .max(min_outer_h),
+    )
+}
+
+/// Computes the minimum logical size that the element's content requires.
+///
+/// Unlike [`intrinsic_size`], this function is designed for window minimum-size
+/// propagation.  The key difference is scroll boxes: a vertically-scrolling box
+/// does not propagate its content height to the window minimum — only its own
+/// explicit `height` or `min_height` contributes.  Flex children without an
+/// explicit size or `min_*` constraint contribute 0 on the main axis (they
+/// can shrink).  Text nodes with no explicit size contribute 0 (they wrap).
+///
+/// The result is in the same coordinate space as [`intrinsic_size`] (outer /
+/// including padding and border insets).
+pub fn element_min_size(element: &Element) -> UiSize {
+    let insets = content_insets(&element.style);
+    let min_outer_w = element
+        .style
+        .min_width
+        .map(|mw| (mw + horizontal_insets(insets)).max(0.0))
+        .unwrap_or(0.0);
+    let min_outer_h = element
+        .style
+        .min_height
+        .map(|mh| (mh + vertical_insets(insets)).max(0.0))
+        .unwrap_or(0.0);
+
+    // Text: can wrap to any width; only explicit size or min_* constrain the window.
+    if element.text_node().is_some() {
+        let w = element
+            .style
+            .width
+            .map(|w| w + horizontal_insets(insets))
+            .unwrap_or(0.0)
+            .max(min_outer_w);
+        let h = element
+            .style
+            .height
+            .map(|h| h + vertical_insets(insets))
+            .unwrap_or(0.0)
+            .max(min_outer_h);
+        return UiSize::new(w, h);
+    }
+
+    // Image: natural size counts as a minimum.
+    if let Some(image) = element.image_node() {
+        let resolved = resolve_image_element_size(element, image.resource.size());
+        return UiSize::new(
+            (resolved.width + horizontal_insets(insets)).max(min_outer_w),
+            (resolved.height + vertical_insets(insets)).max(min_outer_h),
+        );
+    }
+
+    let explicit_w = element.style.width;
+    let explicit_h = element.style.height;
+
+    // Scroll box: content scrolls on the vertical axis; use only explicit/min height.
+    // Width still accumulates child widths (no horizontal scroll yet).
+    if element.scroll_box_node().is_some() {
+        let scroll_gutter = element
+            .scroll_box_node()
+            .map_or(0.0, |sb| sb.scrollbar.gutter_width.max(0.0));
+        let w = explicit_w
+            .map(|w| w + horizontal_insets(insets) + scroll_gutter)
+            .unwrap_or(horizontal_insets(insets) + scroll_gutter)
+            .max(min_outer_w);
+        let h = explicit_h
+            .map(|h| h + vertical_insets(insets))
+            .unwrap_or(vertical_insets(insets))
+            .max(min_outer_h);
+        return UiSize::new(w, h);
+    }
+
+    // Regular container: sum/max children's minimums.
+    if element.children.is_empty() {
+        return UiSize::new(
+            explicit_w
+                .map(|w| w + horizontal_insets(insets))
+                .unwrap_or(horizontal_insets(insets))
+                .max(min_outer_w),
+            explicit_h
+                .map(|h| h + vertical_insets(insets))
+                .unwrap_or(vertical_insets(insets))
+                .max(min_outer_h),
+        );
+    }
+
+    let gap_total = element.style.gap * element.children.len().saturating_sub(1) as f32;
+    let children_min = match element.style.direction {
+        FlexDirection::Column => {
+            let mut width: f32 = 0.0;
+            let mut height = gap_total;
+            for child in &element.children {
+                let child_min = element_min_size(child);
+                // Flex children with no explicit height contribute their min_height only;
+                // if that is also unset they contribute 0 (they can shrink freely).
+                let skip_main = child.style.flex_grow > 0.0 && child.style.height.is_none();
+                width = width.max(child_min.width);
+                if !skip_main {
+                    height += child_min.height;
+                } else {
+                    // Still count the min_height floor even for flex children.
+                    let child_insets = content_insets(&child.style);
+                    let min_h = child
+                        .style
+                        .min_height
+                        .map(|mh| mh + vertical_insets(child_insets))
+                        .unwrap_or(0.0);
+                    height += min_h;
+                }
+            }
+            UiSize::new(width, height)
+        }
+        FlexDirection::Row => {
+            let mut width = gap_total;
+            let mut height: f32 = 0.0;
+            for child in &element.children {
+                let child_min = element_min_size(child);
+                let skip_main = child.style.flex_grow > 0.0 && child.style.width.is_none();
+                if !skip_main {
+                    width += child_min.width;
+                } else {
+                    let child_insets = content_insets(&child.style);
+                    let min_w = child
+                        .style
+                        .min_width
+                        .map(|mw| mw + horizontal_insets(child_insets))
+                        .unwrap_or(0.0);
+                    width += min_w;
+                }
+                height = height.max(child_min.height);
+            }
+            UiSize::new(width, height)
+        }
+    };
+
+    UiSize::new(
+        explicit_w
+            .map(|w| w + horizontal_insets(insets))
+            .unwrap_or(children_min.width + horizontal_insets(insets))
+            .max(min_outer_w),
+        explicit_h
+            .map(|h| h + vertical_insets(insets))
+            .unwrap_or(children_min.height + vertical_insets(insets))
+            .max(min_outer_h),
     )
 }
 
@@ -1486,6 +1837,20 @@ fn child_cross_size(child: &Element, direction: FlexDirection) -> Option<f32> {
     }
 }
 
+fn child_min_main_size(child: &Element, direction: FlexDirection) -> Option<f32> {
+    match direction {
+        FlexDirection::Row => child.style.min_width,
+        FlexDirection::Column => child.style.min_height,
+    }
+}
+
+fn child_min_cross_size(child: &Element, direction: FlexDirection) -> Option<f32> {
+    match direction {
+        FlexDirection::Row => child.style.min_height,
+        FlexDirection::Column => child.style.min_width,
+    }
+}
+
 fn child_flex_weight(child: &Element) -> f32 {
     if child.style.flex_grow > 0.0 {
         child.style.flex_grow
@@ -1501,6 +1866,26 @@ fn main_axis_padding(edges: Edges, direction: FlexDirection) -> f32 {
     }
 }
 
+fn cross_axis_padding(edges: Edges, direction: FlexDirection) -> f32 {
+    match direction {
+        FlexDirection::Row => edges.top + edges.bottom,
+        FlexDirection::Column => edges.left + edges.right,
+    }
+}
+
+/// Snap a rect to the integer pixel grid.
+///
+/// Origin and far edge are each rounded independently so that adjacent
+/// elements (where one's far edge equals the other's near edge) always
+/// butt flush against each other with no gap or overlap.
+fn snap_rect(r: Rect) -> Rect {
+    let x0 = r.origin.x.round();
+    let y0 = r.origin.y.round();
+    let x1 = (r.origin.x + r.size.width).round();
+    let y1 = (r.origin.y + r.size.height).round();
+    Rect::new(x0, y0, (x1 - x0).max(0.0), (y1 - y0).max(0.0))
+}
+
 fn main_axis_size(size: UiSize, direction: FlexDirection) -> f32 {
     match direction {
         FlexDirection::Row => size.width,
@@ -1522,16 +1907,23 @@ fn main_axis_origin(rect: Rect, direction: FlexDirection) -> f32 {
     }
 }
 
+fn cross_axis_origin(content: Rect, direction: FlexDirection) -> f32 {
+    match direction {
+        FlexDirection::Row => content.origin.y,
+        FlexDirection::Column => content.origin.x,
+    }
+}
+
 fn child_rect(
-    content: Rect,
+    cross_origin: f32,
     direction: FlexDirection,
     main_origin: f32,
     main_size: f32,
     cross_size: f32,
 ) -> Rect {
     match direction {
-        FlexDirection::Row => Rect::new(main_origin, content.origin.y, main_size, cross_size),
-        FlexDirection::Column => Rect::new(content.origin.x, main_origin, cross_size, main_size),
+        FlexDirection::Row => Rect::new(main_origin, cross_origin, main_size, cross_size),
+        FlexDirection::Column => Rect::new(cross_origin, main_origin, cross_size, main_size),
     }
 }
 
@@ -1539,9 +1931,9 @@ fn child_rect(
 mod tests {
     use super::{LayoutCache, 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::text::TextSystem;
 
     #[test]
     fn row_layout_apportions_fixed_and_flex_children() {
@@ -2156,10 +2548,12 @@ mod tests {
         let size = UiSize::new(400.0, 600.0);
         let snap1 = layout_snapshot_with_cache(1, size, &root, &mut text_system, &mut layout_cache);
         let snap2 = layout_snapshot_with_cache(2, size, &root, &mut text_system, &mut layout_cache);
-        assert_eq!(snap1.scene.items, snap2.scene.items, "scene items should be identical");
         assert_eq!(
-            snap1.interaction_tree.root,
-            snap2.interaction_tree.root,
+            snap1.scene.items, snap2.scene.items,
+            "scene items should be identical"
+        );
+        assert_eq!(
+            snap1.interaction_tree.root, snap2.interaction_tree.root,
             "interaction trees should be identical"
         );
     }
@@ -2190,7 +2584,6 @@ mod tests {
 
     #[test]
     fn scroll_culling_skips_off_screen_children() {
-        use crate::tree::ScrollbarStyle;
         let mut text_system = TextSystem::new();
         let mut layout_cache = LayoutCache::new();
 
@@ -2198,12 +2591,14 @@ mod tests {
         let item_height = 40.0;
         let viewport_height = 200.0;
         let n = 100;
-        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()
                     .height(item_height)
-                    .child(Element::text(format!("item {i}"), text_style()))
+                    .child(Element::text(format!("item {i}"), text_style())),
             );
         }
         let root = Element::new().child(scroll_box);
@@ -2214,11 +2609,20 @@ mod tests {
         let snap = layout_snapshot_with_cache(1, size, &root, &mut text_system, &mut layout_cache);
 
         // Only text items within the 200px viewport should appear in the scene.
-        let text_items = snap.scene.items.iter().filter(|item| {
-            matches!(item, DisplayItem::Text(_))
-        }).count();
+        let text_items = snap
+            .scene
+            .items
+            .iter()
+            .filter(|item| matches!(item, DisplayItem::Text(_)))
+            .count();
         // At most 6 text items should be visible (5 fit + 1 partial).
-        assert!(text_items <= 6, "expected <= 6 text items in scene, got {text_items} (culling not working)");
-        assert!(text_items >= 4, "expected >= 4 text items visible, got {text_items}");
+        assert!(
+            text_items <= 6,
+            "expected <= 6 text items in scene, got {text_items} (culling not working)"
+        );
+        assert!(
+            text_items >= 4,
+            "expected >= 4 text items visible, got {text_items}"
+        );
     }
 }

lib/ui/src/lib.rs

@@ -6,6 +6,7 @@
 //! sibling crates.
 
 pub(crate) mod trace_targets {
+    #![allow(dead_code)]
     pub const PLATFORM: &str = "ruin_ui::platform";
     pub const SCENE: &str = "ruin_ui::scene";
     pub const TEXT_PERF: &str = "ruin_ui::text_perf";
@@ -30,7 +31,8 @@ pub use interaction::{
 pub use keyboard::{KeyboardEvent, KeyboardEventKind, KeyboardKey, KeyboardModifiers};
 pub use layout::{
     HitTarget, InteractionTree, LayoutCache, LayoutNode, LayoutPath, LayoutSnapshot, ScrollMetrics,
-    TextHitTarget, layout_snapshot, layout_snapshot_with_cache, layout_snapshot_with_text_system,
+    TextHitTarget, element_min_size, layout_snapshot, layout_snapshot_with_cache,
+    layout_snapshot_with_text_system,
 };
 pub use layout::{layout_scene, layout_scene_with_text_system};
 pub use platform::{
@@ -48,8 +50,8 @@ pub use text::{
     TextStyle, TextSystem, TextWrap,
 };
 pub use tree::{
-    Border, BoxShadow, BoxShadowKind, CornerRadius, CursorIcon, Edges, Element, ElementId,
-    FlexDirection, ScrollbarStyle, Style,
+    AlignItems, Border, BoxShadow, BoxShadowKind, CornerRadius, CursorIcon, Edges, Element,
+    ElementId, FlexDirection, ScrollbarStyle, Style,
 };
 pub use window::{
     DecorationMode, WindowConfigured, WindowId, WindowLifecycle, WindowSpec, WindowUpdate,

lib/ui/src/scene.rs

@@ -80,6 +80,9 @@ impl Color {
     /// safe to reserve as a sentinel.  No user-facing API sets this value directly.
     pub const SENTINEL: Self = Self::rgba(0, 0, 0, 0);
 
+    pub const BLACK: Self = Self::rgb(0, 0, 0);
+    pub const WHITE: Self = Self::rgb(255, 255, 255);
+
     pub const fn rgba(r: u8, g: u8, b: u8, a: u8) -> Self {
         Self { r, g, b, a }
     }
@@ -219,6 +222,7 @@ impl Deref for PreparedText {
 
 impl PreparedText {
     /// Construct a `PreparedText` from shaped data.  Called by `TextSystem::prepare_spans`.
+    #[allow(clippy::too_many_arguments)]
     pub(crate) fn from_layout(
         element_id: Option<ElementId>,
         text: String,
@@ -623,10 +627,18 @@ impl DisplayItem {
     /// Return a copy of this item with all positions shifted by `offset`.
     pub fn translated(&self, offset: Point) -> Self {
         fn translate_rect(r: Rect, o: Point) -> Rect {
-            Rect::new(r.origin.x + o.x, r.origin.y + o.y, r.size.width, r.size.height)
+            Rect::new(
+                r.origin.x + o.x,
+                r.origin.y + o.y,
+                r.size.width,
+                r.size.height,
+            )
         }
         match self {
-            Self::Quad(q) => Self::Quad(Quad { rect: translate_rect(q.rect, offset), ..*q }),
+            Self::Quad(q) => Self::Quad(Quad {
+                rect: translate_rect(q.rect, offset),
+                ..*q
+            }),
             Self::RoundedRect(r) => Self::RoundedRect(RoundedRect {
                 rect: translate_rect(r.rect, offset),
                 ..*r
@@ -838,8 +850,8 @@ mod tests {
 
     #[test]
     fn prepared_text_vertical_offset_moves_between_lines() {
-        use std::sync::Arc;
         use super::{PreparedTextLine, TextLayoutData};
+        use std::sync::Arc;
 
         let mut text = PreparedText::monospace(
             "abcdwxyz",
@@ -873,7 +885,11 @@ mod tests {
             }
         }
         let orig_size = text.layout.size;
-        text.layout = Arc::new(TextLayoutData { lines, glyphs, size: orig_size });
+        text.layout = Arc::new(TextLayoutData {
+            lines,
+            glyphs,
+            size: orig_size,
+        });
 
         assert_eq!(text.vertical_offset(2, 1), Some(6));
         assert_eq!(text.vertical_offset(6, -1), Some(2));
@@ -892,8 +908,12 @@ mod tests {
         let target_line = &text.lines[1];
         // Lines store LOCAL coords; add text.origin to get absolute window coords for the query.
         let y = text.origin.y + target_line.rect.origin.y + target_line.rect.size.height * 0.5;
-        let start = text.byte_offset_for_position(Point::new(text.origin.x + target_line.rect.origin.x, y));
-        let end = text.byte_offset_for_position(Point::new(text.origin.x + target_line.rect.origin.x + 16.0, y));
+        let start =
+            text.byte_offset_for_position(Point::new(text.origin.x + target_line.rect.origin.x, y));
+        let end = text.byte_offset_for_position(Point::new(
+            text.origin.x + target_line.rect.origin.x + 16.0,
+            y,
+        ));
         let rects = text.selection_rects(start, end);
 
         assert_eq!(rects.len(), 1);

lib/ui/src/tree.rs

@@ -23,6 +23,15 @@ pub enum FlexDirection {
     Column,
 }
 
+#[derive(Clone, Copy, Debug, Default, Eq, PartialEq)]
+pub enum AlignItems {
+    #[default]
+    Stretch,
+    Start,
+    Center,
+    End,
+}
+
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 pub enum CursorIcon {
     Default,
@@ -180,8 +189,13 @@ impl Default for ScrollbarStyle {
 #[derive(Clone, Debug, PartialEq)]
 pub struct Style {
     pub direction: FlexDirection,
+    pub align_items: AlignItems,
+    /// Per-element override of the parent container's `align_items`. `None` means inherit.
+    pub align_self: Option<AlignItems>,
     pub width: Option<f32>,
     pub height: Option<f32>,
+    pub min_width: Option<f32>,
+    pub min_height: Option<f32>,
     pub flex_grow: f32,
     pub gap: f32,
     pub padding: Edges,
@@ -198,8 +212,12 @@ impl Default for Style {
     fn default() -> Self {
         Self {
             direction: FlexDirection::Column,
+            align_items: AlignItems::Stretch,
+            align_self: None,
             width: None,
             height: None,
+            min_width: None,
+            min_height: None,
             flex_grow: 0.0,
             gap: 0.0,
             padding: Edges::ZERO,
@@ -332,6 +350,20 @@ impl Element {
         self
     }
 
+    pub fn min_width(mut self, min_width: f32) -> Self {
+        self.style.min_width = Some(min_width.max(0.0));
+        self
+    }
+
+    pub fn min_height(mut self, min_height: f32) -> Self {
+        self.style.min_height = Some(min_height.max(0.0));
+        self
+    }
+
+    pub fn min_size(self, min_width: f32, min_height: f32) -> Self {
+        self.min_width(min_width).min_height(min_height)
+    }
+
     pub fn flex(mut self, flex_grow: f32) -> Self {
         self.style.flex_grow = flex_grow.max(0.0);
         self
@@ -382,6 +414,16 @@ impl Element {
         self
     }
 
+    pub fn align_items(mut self, align: AlignItems) -> Self {
+        self.style.align_items = align;
+        self
+    }
+
+    pub fn align_self(mut self, align: AlignItems) -> Self {
+        self.style.align_self = Some(align);
+        self
+    }
+
     pub fn cursor(mut self, cursor: CursorIcon) -> Self {
         self.style.cursor = Some(cursor);
         self
@@ -527,11 +569,21 @@ impl Hash for ScrollbarStyle {
     }
 }
 
+impl Hash for AlignItems {
+    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.width.map(f32::to_bits).hash(state);
         self.height.map(f32::to_bits).hash(state);
+        self.min_width.map(f32::to_bits).hash(state);
+        self.min_height.map(f32::to_bits).hash(state);
         self.flex_grow.to_bits().hash(state);
         self.gap.to_bits().hash(state);
         self.padding.hash(state);

lib/ui/src/window.rs

@@ -1,6 +1,6 @@
 //! Common window model types.
 
-use crate::scene::UiSize;
+use crate::scene::{Color, UiSize};
 
 #[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
 pub struct WindowId(u64);
@@ -55,6 +55,7 @@ pub struct WindowSpec {
     pub maximized: bool,
     pub fullscreen: bool,
     pub resizable: bool,
+    pub base_color: Color,
 }
 
 impl WindowSpec {
@@ -72,9 +73,15 @@ impl WindowSpec {
             maximized: false,
             fullscreen: false,
             resizable: true,
+            base_color: Color::rgb(0x08, 0x0C, 0x14),
         }
     }
 
+    pub fn base_color(mut self, color: Color) -> Self {
+        self.base_color = color;
+        self
+    }
+
     pub fn key(mut self, key: impl Into<String>) -> Self {
         self.key = Some(key.into());
         self

lib/ui_platform_wayland/src/lib.rs

@@ -40,6 +40,9 @@ 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,
@@ -145,6 +148,7 @@ enum InternalBackendEvent {
 
 struct State {
     running: bool,
+    fixed_size_request: Option<(u32, u32)>,
     _connection: Connection,
     _compositor: wl_compositor::WlCompositor,
     _surface: wl_surface::WlSurface,
@@ -156,6 +160,8 @@ struct State {
     clipboard_device: Option<wl_data_device::WlDataDevice>,
     cursor_shape_manager: Option<wp_cursor_shape_manager_v1::WpCursorShapeManagerV1>,
     cursor_shape_device: Option<wp_cursor_shape_device_v1::WpCursorShapeDeviceV1>,
+    /// Server-side decoration handle.  Kept alive so the compositor maintains decorations.
+    _decoration: Option<zxdg_toplevel_decoration_v1::ZxdgToplevelDecorationV1>,
     primary_selection_manager:
         Option<zwp_primary_selection_device_manager_v1::ZwpPrimarySelectionDeviceManagerV1>,
     primary_selection_device: Option<zwp_primary_selection_device_v1::ZwpPrimarySelectionDeviceV1>,
@@ -227,6 +233,18 @@ impl State {
     }
 }
 
+fn fixed_size_request_for_spec(spec: &WindowSpec) -> Option<(u32, u32)> {
+    if spec.resizable {
+        return None;
+    }
+    let size = spec
+        .requested_inner_size
+        .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))
+}
+
 fn wayland_cursor_shape(icon: CursorIcon) -> wp_cursor_shape_device_v1::Shape {
     match icon {
         CursorIcon::Default => wp_cursor_shape_device_v1::Shape::Default,
@@ -318,6 +336,8 @@ impl WaylandWindow {
                 manager.get_device(&seat, &qh, ())
             },
         );
+        let decoration_manager: Option<zxdg_decoration_manager_v1::ZxdgDecorationManagerV1> =
+            globals.bind(&qh, 1..=1, ()).ok();
         let surface = compositor.create_surface(&qh, ());
         let xdg_surface = wm_base.get_xdg_surface(&surface, &qh, ());
         let toplevel = xdg_surface.get_toplevel(&qh, ());
@@ -325,6 +345,11 @@ impl WaylandWindow {
         if let Some(app_id) = spec.app_id.as_ref() {
             toplevel.set_app_id(app_id.clone());
         }
+        let decoration = decoration_manager.as_ref().map(|dm| {
+            let deco = dm.get_toplevel_decoration(&toplevel, &qh, ());
+            deco.set_mode(zxdg_toplevel_decoration_v1::Mode::ServerSide);
+            deco
+        });
 
         apply_size_constraints(&toplevel, &spec);
         if spec.maximized {
@@ -352,6 +377,7 @@ impl WaylandWindow {
             surface_target,
             state: State {
                 running: true,
+                fixed_size_request: fixed_size_request_for_spec(&spec),
                 _connection: connection,
                 _compositor: compositor,
                 _surface: surface,
@@ -395,6 +421,7 @@ impl WaylandWindow {
                 last_selection_serial: None,
                 last_pointer_enter_serial: None,
                 cursor_icon: CursorIcon::Default,
+                _decoration: decoration,
             },
         })
     }
@@ -684,6 +711,7 @@ impl WaylandWindow {
     }
 
     pub fn apply_spec(&mut self, spec: &WindowSpec) -> Result<(), Box<dyn Error>> {
+        self.state.fixed_size_request = fixed_size_request_for_spec(spec);
         self.state._toplevel.set_title(spec.title.clone());
         if let Some(app_id) = spec.app_id.as_ref() {
             self.state._toplevel.set_app_id(app_id.clone());
@@ -719,6 +747,14 @@ impl WaylandWindow {
         }
 
         if let Some((width, height)) = self.state.pending_size.take() {
+            trace!(
+                target: "ruin_ui_platform_wayland::resize",
+                width,
+                height,
+                previous_width = self.state.current_size.0,
+                previous_height = self.state.current_size.1,
+                "prepare_frame observed pending size change"
+            );
             self.state.current_size = (width, height);
             self.state.needs_redraw = false;
             return Some(FrameRequest {
@@ -729,6 +765,12 @@ impl WaylandWindow {
         }
 
         if self.state.needs_redraw {
+            trace!(
+                target: "ruin_ui_platform_wayland::resize",
+                width = self.state.current_size.0,
+                height = self.state.current_size.1,
+                "prepare_frame servicing redraw without size change"
+            );
             self.state.needs_redraw = false;
             return Some(FrameRequest {
                 width: self.state.current_size.0,
@@ -1083,6 +1125,7 @@ fn spawn_window_worker(
                 spec.requested_inner_size
                     .unwrap_or_else(|| UiSize::new(800.0, 500.0))
                     .height as u32,
+                spec.base_color,
             ) {
                 Ok(renderer) => renderer,
                 Err(_) => {
@@ -1355,6 +1398,19 @@ fn spawn_window_worker(
                                             );
                                             state_ref.pending_viewport = Some(current_viewport);
                                             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
+                                            // marker so we can immediately send the next configure.
+                                            // Without this, viewport_request_in_flight stays set
+                                            // to the old size forever and the app is never told
+                                            // about the new viewport.
+                                            if state_ref.viewport_request_in_flight
+                                                == Some(scene.logical_size)
+                                            {
+                                                state_ref.viewport_request_in_flight = None;
+                                                maybe_request_pending_viewport(&mut state_ref);
+                                            }
                                             state_ref.window.request_redraw();
                                         } else if !state_ref.window.presentation_ready() {
                                             // Correct scene is ready but the compositor
@@ -1582,6 +1638,8 @@ delegate_noop!(
     State: ignore
         zwp_primary_selection_device_manager_v1::ZwpPrimarySelectionDeviceManagerV1
 );
+delegate_noop!(State: ignore zxdg_decoration_manager_v1::ZxdgDecorationManagerV1);
+delegate_noop!(State: ignore zxdg_toplevel_decoration_v1::ZxdgToplevelDecorationV1);
 impl Dispatch<wl_seat::WlSeat, ()> for State {
     fn event(
         state: &mut Self,
@@ -2072,6 +2130,14 @@ impl Dispatch<xdg_surface::XdgSurface, ()> for State {
         if let xdg_surface::Event::Configure { serial } = event {
             xdg_surface.ack_configure(serial);
             state.configured = true;
+            trace!(
+                target: "ruin_ui_platform_wayland::resize",
+                serial,
+                current_width = state.current_size.0,
+                current_height = state.current_size.1,
+                has_pending_size = state.pending_size.is_some(),
+                "received xdg_surface configure"
+            );
             state.request_redraw();
         }
     }
@@ -2124,7 +2190,37 @@ impl Dispatch<xdg_toplevel::XdgToplevel, ()> for State {
                     height,
                     "received Wayland toplevel configure"
                 );
-                state.pending_size = Some((width, height));
+                let next_size = (width, height);
+                if let Some(expected_size) = state.fixed_size_request {
+                    if next_size != expected_size {
+                        trace!(
+                            target: "ruin_ui_platform_wayland::resize",
+                            width,
+                            height,
+                            expected_width = expected_size.0,
+                            expected_height = expected_size.1,
+                            "ignoring stale toplevel configure for fixed-size window"
+                        );
+                        state.request_redraw();
+                        return;
+                    }
+                }
+                let size_changed =
+                    next_size != state.current_size && state.pending_size != Some(next_size);
+                trace!(
+                    target: "ruin_ui_platform_wayland::resize",
+                    width,
+                    height,
+                    current_width = state.current_size.0,
+                    current_height = state.current_size.1,
+                    pending_width = state.pending_size.map(|size| size.0),
+                    pending_height = state.pending_size.map(|size| size.1),
+                    size_changed,
+                    "processed Wayland toplevel configure"
+                );
+                if size_changed {
+                    state.pending_size = Some(next_size);
+                }
                 state.request_redraw();
             }
             _ => {}

lib/ui_renderer_wgpu/src/lib.rs

@@ -330,6 +330,7 @@ pub struct WgpuSceneRenderer {
     image_cache_order: VecDeque<u64>,
     #[allow(dead_code)]
     glyph_atlas: GlyphAtlas,
+    base_color: Color,
 }
 
 const MAX_TEXT_CACHE_ENTRIES: usize = 64;
@@ -343,6 +344,7 @@ impl WgpuSceneRenderer {
         target: impl HasDisplayHandle + HasWindowHandle + Send + Sync + 'static,
         width: u32,
         height: u32,
+        base_color: Color,
     ) -> Result<Self, Box<dyn Error>> {
         let instance = wgpu::Instance::new(wgpu::InstanceDescriptor::new_without_display_handle());
         let surface = instance.create_surface(target)?;
@@ -361,6 +363,15 @@ impl WgpuSceneRenderer {
             .copied()
             .find(wgpu::TextureFormat::is_srgb)
             .unwrap_or(caps.formats[0]);
+        let alpha_mode = if base_color.a < 255
+            && caps
+                .alpha_modes
+                .contains(&wgpu::CompositeAlphaMode::PreMultiplied)
+        {
+            wgpu::CompositeAlphaMode::PreMultiplied
+        } else {
+            caps.alpha_modes[0]
+        };
         let config = wgpu::SurfaceConfiguration {
             usage: wgpu::TextureUsages::RENDER_ATTACHMENT,
             format,
@@ -368,7 +379,7 @@ impl WgpuSceneRenderer {
             height: height.max(1),
             present_mode: wgpu::PresentMode::AutoVsync,
             desired_maximum_frame_latency: 2,
-            alpha_mode: caps.alpha_modes[0],
+            alpha_mode,
             view_formats: vec![],
         };
         surface.configure(&device, &config);
@@ -415,7 +426,7 @@ fn sd_round_rect(point: vec2<f32>, rect: vec4<f32>, radius: f32) -> f32 {
 
 fn rounded_rect_alpha(point: vec2<f32>, rect: vec4<f32>, radius: f32) -> f32 {
     let distance = sd_round_rect(point, rect, radius);
-    return 1.0 - smoothstep(0.0, 1.0, distance);
+    return 1.0 - smoothstep(-0.5, 0.5, distance);
 }
 
 fn blurred_round_rect_alpha(point: vec2<f32>, rect: vec4<f32>, radius: f32, blur: f32) -> f32 {
@@ -553,7 +564,7 @@ fn sd_round_rect(point: vec2<f32>, rect: vec4<f32>, radius: f32) -> f32 {
 
 fn rounded_rect_alpha(point: vec2<f32>, rect: vec4<f32>, radius: f32) -> f32 {
     let distance = sd_round_rect(point, rect, radius);
-    return 1.0 - smoothstep(0.0, 1.0, distance);
+    return 1.0 - smoothstep(-0.5, 0.5, distance);
 }
 
 fn apply_clip_alpha(point: vec2<f32>, clip_rect: vec4<f32>, rounded_clip_rect: vec4<f32>, clip_params: vec2<f32>) -> f32 {
@@ -710,6 +721,7 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
             image_cache: HashMap::new(),
             image_cache_order: VecDeque::new(),
             glyph_atlas,
+            base_color,
         })
     }
 
@@ -792,11 +804,16 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
                     depth_slice: None,
                     resolve_target: None,
                     ops: wgpu::Operations {
-                        load: wgpu::LoadOp::Clear(wgpu::Color {
-                            r: 0.03,
-                            g: 0.04,
-                            b: 0.08,
-                            a: 1.0,
+                        load: wgpu::LoadOp::Clear({
+                            let a = self.base_color.a as f64 / 255.0;
+                            // Premultiplied: multiply RGB by alpha so the compositor
+                            // can blend correctly when alpha_mode is PreMultiplied.
+                            wgpu::Color {
+                                r: (self.base_color.r as f64 / 255.0) * a,
+                                g: (self.base_color.g as f64 / 255.0) * a,
+                                b: (self.base_color.b as f64 / 255.0) * a,
+                                a,
+                            }
                         }),
                         store: wgpu::StoreOp::Store,
                     },
@@ -990,7 +1007,9 @@ fn fs_main(input: VertexOut) -> @location(0) vec4<f32> {
                         bottom: physical.y - image.placement.top + height,
                     },
                     content: image.content,
-                    color: glyph.color_opt.map_or(text.default_color, color_from_cosmic),
+                    color: glyph
+                        .color_opt
+                        .map_or(text.default_color, color_from_cosmic),
                     data: image.data.clone(),
                 });
             }
@@ -1470,7 +1489,11 @@ fn create_glyph_atlas(
 /// Resolve `Color::SENTINEL` to `default_color`; return other colors unchanged.
 #[inline]
 fn resolve_glyph_color(color: Color, default_color: Color) -> Color {
-    if color == Color::SENTINEL { default_color } else { color }
+    if color == Color::SENTINEL {
+        default_color
+    } else {
+        color
+    }
 }
 
 fn color_from_cosmic(color: cosmic_text::Color) -> Color {
@@ -2297,7 +2320,7 @@ fn clip_textured_rect(
 /// return only those glyph indices.  This turns O(all_glyphs) iteration into
 /// O(log(lines) + visible_glyphs) — critical for large text nodes in scroll
 /// boxes where only a few lines are on screen at once.
-fn clip_visible_glyphs<'a>(text: &'a PreparedText, clip: Option<Rect>) -> &'a [GlyphInstance] {
+fn clip_visible_glyphs(text: &PreparedText, clip: Option<Rect>) -> &[GlyphInstance] {
     let Some(clip) = clip else {
         return &text.glyphs;
     };
@@ -2332,7 +2355,12 @@ fn text_texture_key(text: &PreparedText) -> TextTextureKey {
             .map(|bounds| (bounds.width.to_bits(), bounds.height.to_bits())),
         font_size_bits: text.font_size.to_bits(),
         line_height_bits: text.line_height.to_bits(),
-        color: (text.default_color.r, text.default_color.g, text.default_color.b, text.default_color.a),
+        color: (
+            text.default_color.r,
+            text.default_color.g,
+            text.default_color.b,
+            text.default_color.a,
+        ),
         glyphs: text
             .glyphs
             .iter()
@@ -2354,10 +2382,7 @@ mod tests {
         ActiveClip, blend_rgba, build_text_vertices, build_vertices, clip_rect_array,
         push_clip_state, rounded_clip_arrays, text_texture_key,
     };
-    use ruin_ui::{
-        ClipRegion, Color, GlyphInstance, Point, PreparedText, Rect, SceneSnapshot,
-        TextSelectionStyle, UiSize,
-    };
+    use ruin_ui::{ClipRegion, Color, Point, PreparedText, Rect, SceneSnapshot, UiSize};
 
     #[test]
     fn quad_scenes_expand_to_six_vertices_per_quad() {