fix(web): keep the right panel synced with agent edits

[rynfar]

The diff panel, file browser, and file preview loaded once and never refetched.
While an agent edited files the right panel kept showing pre-edit content, so the
user was reading stale state next to a live transcript and had to close and reopen
the panel to see the truth.

Adds useWorkspaceMutationRefresh, which derives a mutation id from the latest
terminal file-change or command-execution activity plus the latest checkpoint, and
refreshes each right-panel resource once per mutation. Completed commands count
because a shell command can change the workspace without reporting the paths it
touched. A file with unsaved local edits stays pending rather than being refreshed
out from under the user.

Adopted from upstream pingdotgg/t3code#8803 (e09b88b6a), cherry-picked clean.

Verified: vp test run --dir apps/web apps/web/src/hooks/useWorkspaceMutationRefresh.test.ts apps/web/src/components/files/projectFilesQueryState.test.tsx
(6 passed), vp run -F @t3tools/web typecheck (exit 0, no errors).

Not exercised in a browser — happy to do a real-client pass on request.

Reviewed and integrated with Claude Opus 5 in Claude Code.

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[github-actions]

Thread transfer impact

✅ Thread transfer remains within every enforced ceiling.

Provider	Metric	Main baseline	This PR	Impact	PR ceiling
Codex	Total thread wire	13.6 KiB	13.6 KiB	+11 B (+0.1%)	15.1 KiB	✅
Codex	Thread snapshot wire	6.9 KiB	6.9 KiB	−2 B (−0.0%)	7.3 KiB	✅
Codex	Live turn WebSocket wire	6.6 KiB	6.6 KiB	+13 B (+0.2%)	7.8 KiB	✅
Codex	Live turn WebSocket decoded	57.2 KiB	57.2 KiB	0 B (0.0%)	66.4 KiB	✅
Codex	Live turn messages	10	10	0 (0.0%)	21	✅
Claude	Total thread wire	13.6 KiB	13.6 KiB	+14 B (+0.1%)	15.1 KiB	✅
Claude	Thread snapshot wire	6.9 KiB	6.9 KiB	0 B (0.0%)	7.3 KiB	✅
Claude	Live turn WebSocket wire	6.6 KiB	6.6 KiB	+14 B (+0.2%)	7.8 KiB	✅
Claude	Live turn WebSocket decoded	58.1 KiB	58.1 KiB	0 B (0.0%)	66.4 KiB	✅
Claude	Live turn messages	10	10	0 (0.0%)	21	✅

Baseline: 9ade80d · PR result: 77c935b · Source CI: success

Scenario and decoded snapshot size

10 historical turns, 5 command tools per turn, 878.9 KiB retained MCP result per historical turn, and a 1.05 MiB retained result in the measured turn.

• Codex decoded thread snapshot: 109.5 KiB
• Claude decoded thread snapshot: 110.2 KiB

Updated in place by a trusted workflow. PR artifacts are strictly validated and never executed.

[rynfar]

Adversarial review found six issues. Four are fixed here; two are noted below for a follow-up decision.

Fixed

1. No coalescing. Every completed file_change/command_execution fired a git status, a full git diff preview, a workspace entry listing and a file read. A 60-tool-call turn went from one refresh (previously keyed on latestTurn.turnId) to roughly 240 RPCs, several of them git subprocesses or full-tree payloads. That is a straight performance regression for the workload Pylon is built for. A burst now lands one trailing refresh.

2. Refreshed on mount. handledTokenRef started null, so the first effect run always refreshed — a cold panel open cancelled and re-issued the read the atom had just started. The DiffPanel code this replaced seeded its ref on first observation for exactly that reason. Opening a panel mid-turn now adopts the current mutation.

3. The file tree collapsed on every agent edit. entriesQuery.refresh() yields a new entries array, retriggering model.resetPaths(treePaths), and FileTreeController.resetPaths rebuilds the PathStore without initialExpandedPaths. Expansion reset to initialExpansion: 1, and the reveal effect is suppressed by handledRevealRef, so the open file's ancestors were not re-expanded either. The file browser is no longer auto-refreshed; its manual refresh is unchanged.

4. Open images re-downloaded and blanked. The cache-buster keyed on the global mutation id rather than anything about the image, so any unrelated tool call re-fetched it. Removed; images use normal caching.

Text previews, the diff panel and git status still refresh — that is where the value was.

The projectFilesQueryState effect shim also now runs cleanups the way React does. Without that a timer-based effect cannot coalesce, and the old shim silently double-scheduled.

Noted, not fixed — your call

• FilePreviewPanel.tsx:826 — the !selectedFilePending gate has no recovery path. FileSaveCoordinator.persistLatest only calls onPendingChange(false) on success, so one failed write pins the surface in pendingFileSurfaceIdsByProject for the session and that file never auto-refreshes again, even after reopening.
• useWorkspaceMutationRefresh.ts:4 — Prime's canonicalToolItemType matches exact name tokens, so NotebookEdit falls through to dynamic_tool_call, which is not in WORKSPACE_MUTATION_ITEM_TYPES. Notebook edits stay stale until the turn checkpoint — the very case this PR exists to fix.

Surface decision: the hook lives in apps/web/src/hooks, not packages/client-runtime, so mobile keeps manual-refresh-only. Deliberate for now — the mobile right panel has a different lifecycle — but flagging it per AGENTS' "hit every surface".

Re-verified: projectFilesQueryState + useWorkspaceMutationRefresh tests pass (6), @t3tools/web typecheck clean.