## Release v0.51.237 — Release HE (stage-q8)
Phase 3 MEDIUM-ring pick (3-factor framework): a real concurrency/state-consistency fix from a regular contributor (@franksong2702, ★★★ 38 merges). The hardest review of the sweep — the dual gate caught **two** silent data-loss bugs across two review rounds.
### Fixed
| PR | Author | Fix |
|----|--------|-----|
| #3475 | @franksong2702 | Cancelling a live turn immediately after send now reliably stops the worker and settles the session to a cancelled state (was: spinner over a blank page). `cancel_stream()` falls back to the live active-run registry (`ACTIVE_RUNS`) + session agent cache when `STREAMS` has already detached, so the worker still receives `interrupt("Cancelled by user")`. `/api/session` reports run-journal active state from the live registry instead of trusting a persisted `active_stream_id`. |
### Pre-release dual gate caught TWO silent data-loss bugs (both fixed + regression-tested)
The PR's refactor moved `agent.interrupt()` ahead of the partial-text/reasoning/tool-call snapshot, and that snapshot was no longer under `streams_lock`:
1. **Codex round 1** — the worker's `finally` (which pops `STREAM_PARTIAL_TEXT`/`STREAM_REASONING_TEXT`/`STREAM_LIVE_TOOL_CALLS` under `STREAMS_LOCK`) could clear those buffers the instant `interrupt()` wakes it, so a cancelled turn **silently lost its already-streamed text**. (Opus reviewed the original and said ship — it assumed the snapshot was still lock-protected; the stale comment claimed so but the code wasn't. Verified against the actual code → Codex was right.)
2. **Codex round 2** — my first fix only snapshotted on the `STREAMS`-present path; the detached `ACTIVE_RUNS`-only path (the case this PR adds) still lost text. Fixed by hoisting the snapshot above the `if stream_present` branch so it runs unconditionally under the lock.
Both fixes have regression tests **verified to fail against the buggy versions** (`test_cancel_preserves_partial_text_when_interrupt_pops_buffers` + `test_cancel_preserves_partial_text_on_detached_active_run_path`).
### Gate results
- **Full pytest suite**: 7481 passed, 9 skipped, 3 xpassed, **0 failed**
- **ruff forward gate**: CLEAN
- **browser-smoke gate**: CLEAN
- **Codex (regression)**: SHIP ONLY WITH FIXES (×2 rounds) → both MUST-FIXes applied → re-reviewed **SAFE TO SHIP**
- **Opus (correctness)**: reviewed the original (SAFE); the shipped version is strictly safer (adds the under-lock snapshot Opus deemed unnecessary)
- Deadlock concern cleared: no path takes `ACTIVE_RUNS_LOCK` then `STREAMS_LOCK`.
Rebased onto current master (streaming.py/routes.py merged clean — no overlap with the #3468 dedup change shipped in HC).
Closes#3475.
Co-authored-by: franksong2702 <franksong2702@users.noreply.github.com>
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