fix(decopilot): clear stuck run-status spinner when live stream is silent

[viktormarinho]

What is this contribution about?

The decopilot chat would stick forever on the run-status spinner "Request received — The run was accepted and queued" even though the run completed server-side and the answer was persisted (confirmed read-only on prod: threads terminal, projected_seq advanced, assistant parts persisted). Root cause is client stream-delivery, not the backend: a fast run's live /stream tail can deliver 0 chunks — the JetStream subject is purged on terminal status before this client's consumer reads it, or a 204 degraded buffer returns permanently with no reconnect — so no finish chunk ever clears runStatusStage. The fix reconciles the spinner against the persisted DB client-side (all in thread-connection.ts): refetchLatestPage self-clears a stuck spinner when it surfaces the turn's reply; a bounded post-POST poll surfaces it when no reconnect ever happens; and a 204 on /stream is now transient (refetch + backoff-reconnect). It's scoped to fresh user turns via an awaitingMessageTurn guard so tool-output/approval continuations keep the live-stream behavior untouched.

Screenshots/Demonstration

N/A — no visual changes; the spinner simply clears instead of hanging. Behavior is covered by an e2e that drives the real browser.

How to Test

1. bun test apps/mesh/src/web/components/chat/store/thread-connection.test.ts — 3 new cases (refetch-clears, poll-clears, 204-transient), red/green verified against the pre-fix code.
2. e2e: packages/e2e/tests/decopilot-spinner-reconcile.spec.ts sends a turn with a silent stream, seeds the persisted reply, and asserts the spinner clears + reply renders without a reload (verified locally red on pre-fix / green on fix).
3. Expected: the chat surfaces the persisted answer and drops the spinner within a couple seconds, with no duplicate re-sends.

Migration Notes

None.

Review Checklist

• PR title is clear and descriptive
• Changes are tested and working
• Documentation is updated (if needed)
• No breaking changes

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Summary by cubic

Fixes the Decopilot chat spinner stuck on "Request received" when the live /stream delivers no chunks. The client now reconciles against persisted messages and treats 204 responses as transient, so the reply shows and the spinner clears without a reload.

• Bug Fixes
  • Clear a stuck spinner when refetchLatestPage surfaces the persisted assistant reply.
  • Add a bounded post-POST reconcile poll for fresh user turns; cancels on stop/dispose.
  • Treat 204 on /stream as transient: refetch latest page and retry with backoff.
  • Scope reconcile to new user messages only; tool-output/approval flows keep live-stream behavior.
  • Add unit tests and an e2e to cover refetch-clear, poll-clear, and 204 recovery.

^{Written for commit ba353e8. Summary will update on new commits.}