Show edit actions promptly after thread submit

[ymichael]

What was wrong

Two async transitions could suppress Edit after submitting a new thread. Provider capability gating waited on the full execution-options/model-discovery path, and navigation could briefly lose the provider facts already loaded by the composer. More importantly, the timeline controller preserved row identity using only the row ID and source-sequence range. The server projects turnRequest.status from pending to accepted onto that same message row without extending its sequence range, so the merge retained the stale pending object indefinitely. Edit requires an accepted message; refresh rebuilt the timeline directly from the accepted server row and made the icon appear.

What changed

The thread detail view now reads capabilities from the lightweight, environment-routed provider roster and reuses composer-warmed provider facts while that roster loads. The timeline merge also includes turn-request fields in its identity signature, so an accepted server projection replaces the pending row instead of being discarded as unchanged. Regression coverage exercises both the post-submit provider fallback and the pending-to-accepted row transition. There are no wire, CLI, guide, or protocol changes.

How you verified

• Added a timeline-merge regression test that fails before the fix by retaining pending and passes after the accepted row replaces it.
• Reproduced the exact flow in the browser: new thread, submit, navigate to the active thread, and confirmed Edit appears without refresh while the Stop run control is still present.
• pnpm exec turbo run test --filter=@bb/client-core --force (238 tests)
• pnpm exec turbo run test --filter=@bb/app --force -- --run src/hooks/queries/system-queries.test.tsx (17 tests)
• pnpm exec turbo run typecheck --filter=@bb/client-core --filter=@bb/app
• pnpm exec turbo run lint --filter=@bb/client-core --filter=@bb/app (0 errors; existing warnings remain)
• pnpm exec prettier --check on the changed source files

Fixes: delayed edit-action visibility (no linked issue).

AGENT GENERATED: by GPT-5