Studio chat approvals: follow-ups from #1975 review #2142

Follow-ups from the review of #1975 (Studio chat approvals, plan review, Escape). None block merge. Parent: #1848.

Worth fixing (non-blocking)

• Plan-verdict logic is duplicated and has diverged. chat-workspace.tsx (planUnavailableReason, respondToPlan, separate in-flight/uncertain sets, viewedSessionId guard) vs side-thread-panel.tsx (plan folded into the ordinary path, no uncertain state for plans). After an ambiguous failure, retry/Escape can be allowed on one surface and blocked on the other. Extract one usePlanVerdictControl hook.
• chat-workspace.tsx is ~3400 lines. Move plan-continuation follow/reattach state into plan-continuation.ts.
• Pending-ask card ternary is copied at 3 sites (chat-transcript.tsx, chat-workspace.tsx, side-thread-panel.tsx). Extract a PendingAskCard.
• resolvePlanAsk maps generic failed_precondition to 409 "stale" (apps/server/src/mecatl/chat.ts). Keep only stale_run_control, ask_not_pending, not_awaiting_plan, or log the underlying code.
• Docs: in user-docs/building/deployment/studio.md, the new Review tool calls and plans heading sits above the unrelated "Review authorization" paragraph.
• Test gaps: 500ms draft-clear boundary (499/500ms); held Escape (repeat: true) cannot fire ask deny / plan iterate / panel / stop; verdict keys with a dialog or menu open (or state in docs that only Escape applies); a planted secret in ask args/diff.

Nitpicks

• Add unmatchedApprovals() to chat-state.ts (the message.tools?.some(approvalMatchesToolCall) check is repeated 7 times).
• Use one key helper: settledAskKeys uses runId\0askId, approvalKey uses a JSON tuple with sessionId.
• plan-continuation.ts: replace the hand-rolled AbortController/deadline/Promise.race with AbortSignal.any([signal, AbortSignal.timeout(ms)]).
• chat-escape.ts: drop the redundant focusin branch in changed(); hoist disarm() and reuse it in the second useEffect.
• stalePlanAsk reuses code stale_run_control, so clients cannot tell a stale plan ask from a stale permission ask.
• runtime.ts copyCapabilities hardcodes storageMigration: false and derives bash from shell; add a comment or fix the schema. Check detail()'s new client.server.compatibility() call does not add a round trip per request.
• ci.yml: STUDIO_REQUIRE_MECATED=1 on the Playwright step is read only by mecated-mock.test.ts, not by chat-approval.spec.ts. Drop it or make the spec honour it.
• Docs: the Escape paragraph duplicates the Keyboard shortcuts page; state once and link.
• Tests: malformed/missing args at card level, unmatched callId permission ask, double-click sends one POST, confirm useRealTimers in afterEach in chat-escape.test.tsx.

Fully or partially written by an AI agent.