Type: layout looks up each style run's face once

Layout kept no record of a run's face, so each paragraph looked up the face
of its first character three times for its line metrics and once more to
shape it. The layout now keeps each run's face the first time it is looked
up and uses it for shaping, for paragraph metrics, for on-path type's empty
line and for the column offset of vertical point type. Glyphs, positions,
bounds and baselines do not change.

A test-only helper lays text out looking every face up at each use, and a
new test requires point, vertical point, area and path type laid out both
ways to match exactly.

The layouts of 5,000 short point type objects take a median of 215 million
CPU cycles of the laying-out thread instead of 236 million in a release
build (11 alternating runs of each build on Windows 11, measured while
other builds were running).

docs/target-app-parity.md

@@ -1379,6 +1379,7 @@ Moved from the ROADMAP's "Shipped so far" on 2026-10-10. Update it when a featur
   With the Perspective Selection tool, holding Shift while moving or copying constrains each object's displacement to the nearest axis or 45° diagonal of its own plane; releasing Shift resumes the raw pointer position, and 5 still moves perpendicular to the plane. Snap to Grid follows the constrained line on the first object's plane and depth.
   When the desktop app opens a document on a thread of its own (#1245), that thread also reads the document's linked files and lays out its type, and the UI thread only adds the finished document: in release builds, the step left on the UI thread takes 0.02 ms instead of 1.04 s for a document with 12 linked 3000 × 2000 TIFFs, and it takes 0.1 ms instead of 0.85 s for one with 300 Auto Size area type objects, every second one in three columns.
   Laying out type keeps each font face's shaping plans, at most 32 per face, so type objects of the same font, script, direction, language and features share one plan: the layouts of a document of 5,000 short point type objects take 59 ms instead of 73 ms in a release build, and the glyphs, bounds and baselines do not change.
+  Laying out type looks up the font face of each style run once and uses it for the run's glyphs and for the line metrics of a paragraph that starts in that run: the layouts of a document of 5,000 short point type objects take a median of 215 million CPU cycles instead of 236 million in a release build (11 alternating runs of each build on Windows 11, measured while other builds were running), and the glyphs, bounds and baselines do not change.
   The Layers panel's Delete Selection, Duplicate Selection, Collect in New Layer, Merge Selected, Flatten Artwork, Release to Layers (Sequence) and row drags also take time in proportion to the size of the document, and so do Cut Artboard and Duplicate Artboard with their art and each move of an Alt-drag of one artboard with the Artboard tool while Move/Copy Artwork with Artboard is on (#1429).
   In Outline view the renderer draws paths and compound paths from the geometry it keeps for them between frames, and it culls the members of clip groups by the bounds it keeps for them. Layers with Preview off and the outlines of Image Trace objects are drawn the same way.
 - **Graphics processor:** the canvas is rasterized on the CPU and the GPU only composites it, so any GPU that can show the window will do. Preferences › Performance › Graphics Processor (`gpuPreference`) is Automatic by default: the power-saving GPU on Windows and macOS (the integrated one on hybrid-graphics laptops, where presenting from the discrete GPU made the window flicker, #306), and the GPU the desktop runs on under Linux, where KWin on an NVIDIA GPU refused frames from a Ryzen's integrated GPU and 0.5.0 crashed at startup (#502). Power Saving and High Performance pick a kind of GPU; `WGPU_POWER_PREF`, `WGPU_ADAPTER_NAME` and `WGPU_BACKEND` override them. The app picks among the adapters that can present to the window (native backends before OpenGL, hardware before software, and on Windows a GPU's DX12 adapter before its Vulkan one: Intel's Vulkan driver made the whole window flicker black, #545), and if the window fails on one while starting up it starts again without it instead of crashing; after a start that a graphics driver crashed before its first frame, the next starts leave that adapter out, or list OpenGL's adapters alone when the crash came while the adapters were being listed (#2243; verified by unit tests, not on the reporter's Intel UHD Graphics 605); Help › About, `ui.inspect` and the log name the adapter in use. When the browser drops the page's WebGPU device or WebGL context, the web build writes recovery copies, starts again on new graphics with the same app and uploads its textures again; if it can't, it removes the stale canvas and says to reload, which offers the copies back. The desktop app writes the copies and says to restart (#369). On Windows and Linux the tools' cursors are OS cursors (bitmaps rasterized once per display scale), which the system moves itself: painted into the window, they trailed the pointer by the frames waiting to be shown, and the window now queues one frame instead of two (#444). macOS and the web still paint them (macOS sizes cursor bitmaps in points, eframe has no bitmap cursors on the web). Tool states have cursors of their own as the public manual describes them: Direct Selection shows a hollow or filled square on its white arrow over an anchor (path unselected or selected) and the Reshape Segment cursor over a curved segment, as do the Anchor Point tool and the Pen with Alt (whose caret it lends); Group Selection, and Direct Selection with Alt, show a plus; a drag shows the filled arrow, hollow while it snaps to a point or a guide, and an Alt-drag copy a double arrowhead; Curvature has its own pen and Free Transform's Cmd/Ctrl side-shear two arrows passing along the side. Lasso, Magic Wand, the freehand tools, Shaper, Live Paint Bucket, Measure, Print Tiling, the symbolism tools, vertical type, Scissors, Mesh and Puppet Warp return cursors of their own, which borrow the crosshair, the I-beam, the Pen's add cursor or not-allowed until they're drawn; there's no busy cursor yet. `crates/tools/src/cursors.toml` lists every cursor, when it shows and its hotspot, for whoever draws them. Pens and touch drive the tools as the mouse does, and a tap pressed and lifted within one frame clicks where it tapped (#491); pen pressure reaches the Paintbrush's pressure-sensitive brushes and the Liquify tools' Use Pressure Pen on Windows, on the web and on Linux under X11 and XWayland, while winit 0.30 reports none on macOS or native Wayland. On Linux, see `docs/development.md` for pens under Wayland.