Revert #10: scope assistant message ids by turn after resume

[justingray0]

Summary

Reverts #10 (turn-scoped assistant message ids) in favor of adopting upstream pingdotgg#3669, which fixes the same resumed-session ordering bug at the source (runtime-unique ACP segment item ids) and additionally fixes cancel-as-notification, agent thought rendering, and a turn-completion drain race.

This is step 1 of that migration:

1. (this PR) revert fix(cursor): scope assistant message ids by turn after resume #10's downstream turn-scoping in ProviderRuntimeIngestion.ts
2. sync fork main with upstream/main
3. adopt Fix Cursor ACP thread rendering, thought output, and cancel delivery pingdotgg/t3code#3669 as a local PR

Notes

• Reverting to the exact pre-fix(cursor): scope assistant message ids by turn after resume #10 tree (identical to fix(cursor): harden ACP session resume and provider recovery #9's fix/cursor-acp-resume state) — known-good, compiles.
• fix(cursor): harden ACP session resume and provider recovery #9's resume/recovery hardening (ProviderSessionRecovery.ts, replay gating, activeTurnId sync) is kept — it has no upstream equivalent.
• The real-Cursor resume E2E (cursorResume.integration.test.ts) removed here will be re-added on top of Fix Cursor ACP thread rendering, thought output, and cancel delivery pingdotgg/t3code#3669 in step 3 as the stronger regression guard.

Co-Authored-By: Claude Opus 4.8 noreply@anthropic.com