feat: add React acpmux agent pane

[teamleaderleo]

The agent session pane now has a React TypeScript renderer that connects directly to the acpmux daemon over its authenticated loopback WebSocket. Native remains the default while the TypeScript pane is validated against the same event stream and seeded transcript path.

What changed

• Reduced the Swift bridge to a versioned host handshake. Swift starts or finds acpmux and returns the loopback WebSocket endpoint, a daemon bearer token for the web-view launch, and the selected session id. It continues to host WKWebView, customization files, and native-only actions.
• Added a direct React acpmux client. It initializes, watches sessions, attaches with _acpmux/attach {eventStream: true}, pages older events with beforeSeq, folds mux and ACP events into rows, and sends ACP and _acpmux/* actions directly.
• Reconciled permission envelopes, optimistic prompt echoes, and stream row state across turns, with focused direct-client tests.
• Kept the React renderer requested by Leo. Rows are memoized by row id and content version, with Pretext-based named-font measurement, cached markdown blocks, typed-array geometry, binary-search virtualization, latest-message opening, and scroll anchoring.
• Kept registry-based React row renderers and composer chips. User components can provide a deterministic measure(row, width) function; components without one use anchored post-mount measurement. theme.css, layout.json, and registry.js hot reload from ~/.config/cmux/agent-pane/.
• Kept the standalone Vite preview harness with Codex and Claude-shaped event recordings, real-speed streaming replay, the 5,000-row transcript, permission and queue fixtures, fixture picker, theme and width controls, and frame-time readout.
• Native remains the default renderer.

The listener is loopback and already authenticates WebSocket handshakes with the daemon bearer token. WKWebView cannot set an Authorization header, so the host passes the token in the query string accepted by acpmux. The token is only handed to the local web view; Swift does not persist or relay transcript data through the bridge.

The React pivot follows the projections rules in cmuxterm-hq#1051, with the correction that acpmux owns sessions, Swift hosts, and React and native are both clients. This branch includes the merge from origin/main at 2e8363e637c, which Lawrence can pull into #15521 when his branch catches up.

Preview

cd webviews
bun run preview:dev
bun run preview:build

The static output is webviews/dist/acpmux-agent-session-preview/ and uses relative assets for file or static-host use.

Validation

• bun x tsgo --noEmit
• bun test src/agent-session/acpmux/model.test.ts src/agent-session/acpmux/direct.test.ts (8 passed)
• focused oxlint on the direct client and preview
• bun run preview:build
• ./scripts/build-agent-session-web.sh
• python3 scripts/verify-local.py --swift-changed --only swift-syntax --only project --only config-schema --only localization --only test-wiring
• Swift package tests need macOS CI because this Linux host cannot import the package's existing Darwin dependency.

Performance

Lawrence's native debug.agent_chat.action seed_rows fling measured p50 and p95 at 8.33 ms on a 120 Hz display. The TypeScript pane exposes the same seed and fling stats actions; comparable macOS/fleet numbers are still pending.

Changelog

Changed: React agent pane now connects directly to acpmux and folds its authenticated event stream in TypeScript; Swift hosts the web view and native remains the default.

Latest repair at bd3f0416cc9 preserves live events received during attach, marks rejected optimistic sends failed, and reconciles prompt echoes from older daemons without promptId.

Lifecycle repair at 353b636ac25 adds reconnect and first-session creation, resets per-session sequence state, removes superseded retry rows, and persists React session selection through the host.

The final repair persists a newly created session before its first prompt is sent, including when that prompt is still streaming or rejects.

The final repair drops stale concurrent session selections before they can overwrite the persisted current session.

The final attach guard ignores stale responses from overlapping session selections before they can change the active pane.

The final repair recovers cleanly when acpmux purges the selected session, including while reconnecting after a socket drop.

The final purge repair clears queued and streaming state before attaching a replacement session.

[github-actions]

CI failure attribution

CI stopped on 353b636ac2 (run 36757370934 attempt 1): 1 code, 3 unknown.

Job	Verdict	Why
suite-coverage	unknown	no known signature; failed step: Require the suite that judges this diff
web / agent-session-web-resources	unknown	no known signature; failed step: Build and test Agent Session web resources
guards / workflow-guard-tests / preflight	code	a Python test failed
guards / workflow-guard-tests / release-ios	unknown	no known signature; failed step: Validate iOS package conventions for this change

Matched log lines

guards / workflow-guard-tests / preflight: FAIL: test_every_advertised_path_is_supported (__main__.ConfigurationReviewPathsTests.test_every_advertised_path_is_supported)

Not re-run automatically: suite-coverage, web / agent-session-web-resources, guards / workflow-guard-tests / preflight, guards / workflow-guard-tests / release-ios are not machine failures.

Written by scripts/ci/classify_failures.py (ci-failure-attribution.yml); signatures are its SIGNATURES table. A machine verdict is the runner's fault, not this PR's.

[github-actions]

Dogfood tours of 353b636a

sidebar-and-chrome-tour at 353b636a: not run

skipped: CI left no app build for this head (its compile failed or was cancelled)

_{Tours are picked by the paths globs in dogfood/scenarios/*.json; a Dogfood-tours: a, b line in the description picks them instead (none turns this off). Look at every frame before merging: a green tour only means no step failed.}

[teamleaderleo]

Review at 3ba6b383b1f: the direction change was checked against the acpmux listener and schema. The listener serves WebSocket text frames on the dashboard port and accepts its bearer token in the query string, which lets WKWebView connect without an Authorization header.

Fixed: Swift no longer projects transcript rows or handles chat mutations for the web pane; the host bridge returns only the authenticated endpoint, launch token, and selected session. React now initializes, watches, attaches with eventStream, folds mux and ACP events, pages with beforeSeq, and sends ACP actions directly. Preview recordings use the same event-stream shape.

Left: macOS Swift package tests, CI, and a live 5,000-row macOS fling measurement remain pending. Native remains the default.

[teamleaderleo]

Review at 353b636: PASS. The fresh review exercised purge reset, replacement attach, reconnect after purge, overlapping attach guards, superseded streams, and packaged asset parity; 8 focused tests passed.
Fixed: direct client lifecycle races, first-session creation and persistence, stale attach isolation, superseded retry rows, purge recovery, and the generated resource bundle.
Left: Swift package tests and comparable macOS fling numbers remain CI or fleet validation.