Fix stale background response state after renderer recovery

[sambitcreate]

Summary

• reconcile retained detached generations from main-process settlement and activity events
• refresh the exact transcript and chat list before clearing renderer ownership
• require a fresh authoritative inactive snapshot and clear only captured stream IDs, preserving genuinely active or newer work
• recover the same state during root bootstrap when a terminal event was missed during a route error

Production incident

A completed chat could remain stuck on “Response continues in the background…” with a sidebar spinner after a renderer route error. Main had durably persisted and settled the generation, but the renderer retained its detached lifecycle owner after missing the one-shot terminal payload.

Verification

• npx tsx --test renderer/lib/chat-terminal-sync.test.ts renderer/main/chat-transition.test.tsx
• npm run type-check
• npm run lint
• npm test
• npm run build

The regressions cover missed terminal delivery, genuine active work, same-chat newer-generation races, workspace isolation, and root recovery subscription ordering.

[pullfrog]

✅ No new issues found.

Reviewed changes — initial review of the detached-generation recovery fix at 6bfd04c4, verified with the focused and adjacent suites plus npm run type-check and lint.

• renderer/lib/chat-terminal-sync.ts — adds DetachedLifecycleChatReconciliation, pendingDetachedLifecycleChats(), captureDetachedLifecycleChat() (exact stream-id capture at event time), and clearInactiveDetachedLifecycleChat(), which removes only the captured ids from the detached/fallback/projection maps and re-validates chat+workspace against the current owner before deleting.
• renderer/main/root-view.tsx — reconcileDetachedLifecycleChat() waits for bounded main idle, refetches the exact transcript and chat list, then reads a fresh activity snapshot and clears only when the chat is inactive; the chats:settled handler now routes through it, and a new effect subscribes to chats:activity-changed before its one-shot bootstrap snapshot so a settle transition cannot fall between the two.
• renderer/lib/chat-terminal-sync.test.ts / renderer/main/chat-transition.test.tsx — behavioral coverage for inactive repair, active preservation, same-chat newer-generation exactness, and workspace isolation, plus a source-contract test pinning the subscribe-before-snapshot ordering and the clear-after-fresh-snapshot wiring.
• .papercuts/troubleshooting.md — investigation notes for the incident.

Two independent deep passes (mine plus two focused subagent traces) found no path where the new clear deletes still-running work — waitForChatIdle gates on generation ownership, the clear uses a snapshot taken after the refetch, and newer same-chat streams are excluded by capture — and no app-reachable path where a retained owner survives indefinitely. The residual best-effort property (a failed bootstrap snapshot read with no later activity event) is already documented in the code comments.

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