Build interactive native workspace vertical slice

docs/UI_SPIKE_SCORECARD.md

@@ -10,8 +10,8 @@ from macOS and Linux and the hard gates pass.
 | Builds on Ubuntu | yes | conditional | pass |
 | Builds on Omarchy/Arch | yes | pending | pending |
 | Dependency/license closure permits Apache-2.0 distribution | yes | pending | pending |
-| Keyboard navigation + AccessKit tree | yes | pending | pending |
-| IME and composed Unicode input | yes | pending | pending |
+| Keyboard navigation + AccessKit tree | yes | keyboard pass; current-GPUI semantics compile; platform AT pending | fail: no AccessKit integration at pinned revision |
+| IME and composed Unicode input | yes | framework API exists; end-to-end pending | editor API exists; end-to-end pending |
 | Isolated system browser child | yes | pending | pending |
 | Cold startup, p50/p95 | record | pending | pending |
 | Idle RSS / six-stream RSS | record | pending | pending |
@@ -43,4 +43,50 @@ performance numbers. GPUI's Ubuntu row remains conditional because the host has
 the runtime `libxkbcommon-x11.so.0` but lacks the unversioned development linker
 name normally supplied by `libxkbcommon-x11-dev`. Floem current main also
 requires its `editor` feature for the style/label modules used by this shell;
-that feature is now explicit in the spike. Neither finding decides the UI stack.
+that feature is now explicit in the spike. Neither build result by itself
+decides the UI stack.
+
+## Accessibility gate and provisional direction
+
+The published `gpui 0.2.2` used by the visual shell has focus and keyboard
+actions but does not expose the current AccessKit element API. An isolated probe
+therefore pins GPUI directly to Zed commit
+`ce48461eaadd16c65c31f835511ab96bd3b6e746` with its matching Rust 1.97.1
+toolchain. The real element wiring compiles with stable accessibility IDs,
+workspace/pane/terminal roles, selected state, focus tracking, and a needs-input
+description. The same probe installs real `EntityInputHandler` and
+`ElementInputHandler` implementations and tests marked-text commit, a composed
+accent, and a multi-codepoint emoji without splitting UTF-8. Three deterministic
+tests pass. AT-SPI/OS IME on Linux and VoiceOver/IME on macOS remain end-to-end
+gates.
+
+The pinned Floem revision has keyboard focus and editor IME plumbing but no
+AccessKit dependency or semantic tree. That fails Lumbridge's accessibility
+gate without a maintained framework fork or adapter. The provisional direction
+is therefore **GPUI-first using current Zed GPUI behind a narrow Lumbridge UI
+adapter**. The published GPUI shell remains the lightweight interaction and
+visual benchmark until the dependency/toolchain migration is accepted.
+
+This is not the final cross-platform release decision. Current-GPUI validation
+on amd-server required a 624 MiB Rust 1.97.1 toolchain, a 691-package lockfile,
+and 4.4 GiB of debug artifacts across check, test, Clippy, and build. Packaging,
+license closure, IME, platform assistive technology, browser parenting, macOS,
+and Omarchy still have to pass.
+
+The comparable Floem shell passes build, test, strict Clippy, live rendering,
+streaming, mouse selection, and numeric pane selection on metal. Its command
+palette opens through the visible clickable affordance and uses Floem's native
+`TextInput`, but Ctrl/Cmd+K did not reach the handler in the X11 automation
+probe. That unresolved focus/event-routing behavior is another current strike
+against adopting Floem; it is recorded rather than hidden behind the clickable
+fallback.
+
+## Measurement semantics
+
+Both renderers consume the same deterministic six-surface action stream. Each
+tick invalidates six surfaces, appends one bounded line to each of the three
+terminal fixtures, and records stable event/revision counters. The GPUI footer
+currently reports dispatch-to-element-build p50/p95 over a bounded 256-sample
+window. It is deliberately not called key-to-present or frame-present latency:
+neither candidate exposes a reliable public cross-platform post-present
+callback. True present latency requires an external platform probe.