event_loop, a11y, text_shaping: AccessKit AT-SPI2 bridge, cross-app clipboard, xdg-activation, HarfBuzz shaping, multi-touch hooks

Five orthogonal capabilities land together because they share the same `try_run` plumbing: an optional global is bound at startup, a piece of state is added to `AppData`, the run-loop iteration drains an inbox / pushes a frame snapshot, and the public surface gains a small set of opt-in `App` hooks. Nothing here breaks an existing app — every new path degrades to a no-op when the compositor does not advertise the relevant global or when the platform adapter cannot start.
AT-SPI2 accessibility via AccessKit. A new `src/a11y/` module owns the platform adapter and the inbound `ActionRequest` channel. `A11yState::try_new` constructs an `accesskit_unix::Adapter`; when the AT-SPI2 daemon is not on the session bus (headless CI, locked-down compositors) the constructor returns `None` and the rest of the pipeline runs unchanged. After every successful `draw_frame`, the run loop builds a fresh `accesskit::TreeUpdate` from `widget_rects` and pushes it through the adapter — main surface plus every visible overlay, each translated to global coordinates via `surface_offset_for` so screen readers report positions in the same frame the user sees. Buttons / toggles / checkboxes / radios / list items / sliders / text edits map to the matching `Role`s; `Click` and `Focus` actions are advertised on every interactive node; inbound action requests are drained at the top of each iteration and translated into a synthetic press / focus on the matching widget. The integration is documented as best-effort in `docs/architecture.md` under "Known gaps and non-goals": hierarchical nesting, per-widget accessible names, live regions and `Action::SetValue` are listed as the natural follow-ups that the foundation now supports but does not yet wire.
Cross-application clipboard via `wl_data_device_manager`. A new `src/event_loop/data_device.rs` bridges the existing process-local `clipboard: String` to the Wayland selection. Outbound (Ctrl+C / Cut): after the local clipboard is populated, `publish_clipboard_selection` creates a `CopyPasteSource` offering `text/plain;charset=utf-8` and installs it as the seat's selection; `DataSourceHandler::send` writes the cached string into the fd the peer hands us. Inbound (Ctrl+V from another app): `DataDeviceHandler::selection` asks for the offered text via `WlDataOffer::receive`, spawns a tiny worker thread to drain the read pipe with a 16 MiB cap to prevent paste-bomb DoS, and posts the result back through an `mpsc::Sender` that the run loop drains each iteration into `data.clipboard`. The `clipboard:` field's doc-comment is updated to reflect the new behaviour: process-local when the compositor does not advertise the global, synchronised with the seat selection otherwise.
External drag-and-drop reception. The same `data_device` module handles `DragOffer` enter / motion / leave / drop_performed: `on_drop_motion( x, y )` fires while the drag hovers over the surface, `on_drop_leave()` when it withdraws without dropping, and `on_drop_received( x, y, mime, text )` when an external payload (`text/uri-list`, `text/plain`, …) is released on top of an ltk window. The receive path reuses the same worker-thread / channel pattern as the clipboard so the run loop never blocks on the read fd. Three new `App` hooks expose the events with no-op defaults; apps that ignore them get the previous behaviour.
`xdg-activation-v1`. The global is bound optionally; when it is present, `try_run` reads `$XDG_ACTIVATION_TOKEN` from the environment, removes it immediately (single-use; preventing leaks into child processes) and stashes it on `AppData::activation_token_pending`. After the first successful configure of the main surface — the earliest point at which `xdg_activation_v1.activate` is meaningful — the token is consumed once and the surface raised to focus. Compositors without the global leave `activation_state` as `None` and the inbound path silently degrades. An `App::request_activation_token` outbound path is reserved on the trait but not yet exercised here.
HarfBuzz shaping. A new `src/text_shaping.rs::shape_line` drives both renderers: the logical-order string is run through `unicode-bidi`, split into per-font sub-runs, and shaped through `rustybuzz`. Each `PositionedGlyph` carries the per-font `glyph_id`, the visual advance and the ink offsets — exactly what `fontdue::Font::rasterize_indexed` needs to render Arabic connected forms, Devanagari clusters and CJK shaped glyphs correctly. The GLES atlas is re-keyed on `(glyph_id, size_bits, font_id)` so glyphs from different fonts at the same size no longer collide, and the atlas format is selected per ES profile (`GL_R8` / `GL_RED` on ES3, `GL_LUMINANCE` on ES2) — the fragment shader samples `.r` for both, since `GL_LUMINANCE` replicates the coverage byte into `.r=.g=.b`. Software path follows the same key. New `Cargo.toml` deps: `unicode-bidi = "0.3"`, `rustybuzz = "0.14"`.
Multi-touch hooks. `App::on_touch_down / on_touch_move / on_touch_up( id, x, y )` expose the raw `wl_touch.id` of every secondary finger. The first finger to land remains the *primary slot* and is fed through the regular gesture machine (`on_pointer_*`, swipe, scroll, long-press, drag-and-drop). Every additional finger fires the new callbacks instead, leaving the existing single-slot behaviour untouched for apps that do not override them. This is the substrate for app-defined pinch-zoom / two-finger pan; the toolkit itself does not yet ship a built-in pinch gesture (called out in the same "Known gaps" doc section).
`event_loop::frame` extracted from `draw/mod.rs`. The `draw_frame` orchestrator and its per-format SHM helper (`pick_shm_format`) move into `src/event_loop/frame.rs`, leaving `draw/` strictly responsible for per-surface paint primitives. The import in `event_loop/run.rs` is rewritten accordingly; `draw/mod.rs` shrinks from 192-line orchestrator to a thin module index.
Overlay teardown safety. `AppData::discard_overlay( id )` synchronously removes a destroyed overlay from the map and rewrites every per-device focus that pointed at it (pointer, keyboard, every touch slot), migrating an in-flight long-press drag to the main surface the same way `reconcile_overlays` does. Used by the compositor-driven destruction paths (`PopupHandler::done`, `LayerShellHandler::closed`) where waiting for the next reconcile would leave a window in which `surface()` / `surface_mut()` panic. The non-panicking siblings `try_surface` / `try_surface_mut` are added for callers on async dispatch paths (IME `Done`, tooltip arm) that may race a teardown.
Miscellaneous. CI: `master` → `main` to match the actual default branch. `Makefile` adds `cargo run --example dialog` to the examples target. `src/lib.rs` re-exports `widget::scroll::ScrollAxis` so apps can configure a `scroll()` axis without reaching into a `pub(crate)` module. `Cargo.toml` adds `accesskit = "0.17"` and `accesskit_unix = "0.13"`. `docs/architecture.md` gains the "Known gaps and non-goals" section that enumerates the new capabilities, what still ships flat, and what is deferred (per-widget a11y labels, primary selection, intra-process multi-touch gestures, `wp_fractional_scale_v1`).

src/system_fonts.rs

@@ -26,6 +26,22 @@ use std::sync::{ Arc, OnceLock };
 
 use fontdue::{ Font, FontSettings };
 
+/// Bytes-aware font handle. The `font` is what fontdue rasterises
+/// against; `bytes` is the raw OpenType / TrueType buffer that
+/// rustybuzz (HarfBuzz) requires for shaping. They are owned
+/// separately because fontdue does not expose its internal byte
+/// buffer — we keep both alive in lockstep instead.
+///
+/// `face` is the TTC sub-face index (0 for single-face files, the
+/// face index for collections like Noto Sans CJK).
+#[ derive( Clone ) ]
+pub struct FontHandle
+{
+	pub font:  Arc<Font>,
+	pub bytes: Arc<Vec<u8>>,
+	pub face:  u32,
+}
+
 /// Per-script fallback font path with the TrueType-collection face
 /// index fontdue should load (most files are single-face → 0; CJK
 /// `.ttc` archives carry many faces, see the SC face on the canonical
@@ -78,9 +94,9 @@ const FALLBACK_FONT_CANDIDATES: &[ FallbackFontSpec ] =
 /// doesn't drag the CJK pack into memory. `None` inside a resolved
 /// slot means the file was missing or fontdue rejected it — a sticky
 /// negative result so subsequent misses skip the slot in O(1).
-fn slots() -> &'static [ OnceLock<Option<Arc<Font>>> ]
+fn slots() -> &'static [ OnceLock<Option<FontHandle>> ]
 {
-	static SLOTS: OnceLock<Vec<OnceLock<Option<Arc<Font>>>>> = OnceLock::new();
+	static SLOTS: OnceLock<Vec<OnceLock<Option<FontHandle>>>> = OnceLock::new();
 	SLOTS.get_or_init( ||
 	{
 		( 0..FALLBACK_FONT_CANDIDATES.len() )
@@ -90,9 +106,11 @@ fn slots() -> &'static [ OnceLock<Option<Arc<Font>>> ]
 }
 
 /// Try to load and parse the fallback font at slot `idx`. Each
-/// `OnceLock` wraps `Option<Arc<Font>>` so a missing or malformed
-/// file is recorded as `None` and never re-attempted.
-fn slot_font( idx: usize ) -> Option<Arc<Font>>
+/// `OnceLock` wraps `Option<FontHandle>` so a missing or malformed
+/// file is recorded as `None` and never re-attempted. The raw bytes
+/// are preserved inside the handle so the same `Arc<Vec<u8>>` can be
+/// handed to rustybuzz for shaping without re-reading the file.
+fn slot_handle( idx: usize ) -> Option<FontHandle>
 {
 	let slot = &slots()[ idx ];
 	slot.get_or_init( ||
@@ -100,10 +118,15 @@ fn slot_font( idx: usize ) -> Option<Arc<Font>>
 		let spec  = &FALLBACK_FONT_CANDIDATES[ idx ];
 		let bytes = std::fs::read( spec.path ).ok()?;
 		let opts  = FontSettings { collection_index: spec.face, ..FontSettings::default() };
-		Font::from_bytes( bytes.as_slice(), opts ).ok().map( Arc::new )
+		let font  = Font::from_bytes( bytes.as_slice(), opts ).ok()?;
+		Some( FontHandle
+		{
+			font:  Arc::new( font ),
+			bytes: Arc::new( bytes ),
+			face:  spec.face,
+		} )
 	} )
-		.as_ref()
-		.map( Arc::clone )
+		.clone()
 }
 
 /// Find the first fallback font that has a non-zero glyph index for
@@ -120,13 +143,22 @@ fn slot_font( idx: usize ) -> Option<Arc<Font>>
 /// scripts (Devanagari, Arabic, …) whose total weight is a fraction
 /// of the CJK pack everyone was paying for unconditionally.
 pub fn lookup( ch: char ) -> Option<Arc<Font>>
+{
+	lookup_handle( ch ).map( |h| h.font )
+}
+
+/// Bytes-aware variant of [`lookup`]. Returns the full
+/// [`FontHandle`] (fontdue handle + raw bytes + face index) so
+/// callers that need to invoke a HarfBuzz-style shaper can do so
+/// without re-reading the font file.
+pub fn lookup_handle( ch: char ) -> Option<FontHandle>
 {
 	for idx in 0..FALLBACK_FONT_CANDIDATES.len()
 	{
-		let Some( font ) = slot_font( idx ) else { continue };
-		if font.lookup_glyph_index( ch ) != 0
+		let Some( handle ) = slot_handle( idx ) else { continue };
+		if handle.font.lookup_glyph_index( ch ) != 0
 		{
-			return Some( font );
+			return Some( handle );
 		}
 	}
 	None