chore(release): 0.17.0 (rebuild) — +circuit-breaker lock unification

[maltsev-dev]

Summary

Rebuild of the 0.17.0 release (#101 already merged 2756862) to include the circuit-breaker lock unification fix (DEF-CB-LOCK-UNIFICATION-2026-09-12) — the original PR was merged and the local tag is prepared, but PyPI publish hadn't fired yet (v0.17.0 was never pushed to origin), so we still have a clean window to fold the new fix into 0.17.0 instead of shipping it as a 0.17.1 hotfix.

The 0.16.8 → 0.17.0 release now carries four correctness themes instead of three. The new theme closes a sync↔async race in NullRunCircuitBreaker: pre-fix the sync path held threading.Lock (self._lock) and the async path held a separate asyncio.Lock (_async_lock), with no mutual exclusion between them. A sync thread calling breaker.call(sync_fn) and an async coroutine calling await breaker.call(async_fn) on the same breaker instance could both write self._state concurrently. The async critical sections contain no await between attribute writes, so asyncio's single-threaded scheduler already serialises them — the _async_lock was dead weight. Fix removes _async_lock; both paths now use self._lock. async with self._lock blocks the event loop for zero observable time on the happy path (no await in the critical section).

The three original themes (Token discipline, gate-cache staleness closure, lazy-export repair) are unchanged from the merged PR #101 — this rebuild only adds the circuit-breaker theme on top.

No wire-format change. SDK_MIN_VERSION unchanged. /gate, /execute, /track, /cancel payloads are byte-identical to 0.16.8 and to the original #101 0.17.0 release.

Fixed

• DEF-CB-LOCK-UNIFICATION-2026-09-12 — NullRunCircuitBreaker now serialises sync + async critical sections on a single threading.Lock (src/nullrun/breaker/circuit_breaker.py, 77bf38b). Pre-fix the sync path held self._lock (threading.Lock) and the async path held a separate asyncio.Lock (_async_lock, lazy-init via _get_async_lock); on the same breaker instance a sync thread calling breaker.call(sync_fn, ...) and an async coroutine calling await breaker.call(async_fn, ...) could both write self._state concurrently. The async critical sections contain no await between attribute writes; with asyncio's single-threaded execution model those sections are already atomic under the GIL+scheduler — the _async_lock was dead weight providing no additional exclusion. Fix: removed _async_lock and _get_async_lock; both paths now use self._lock. async with self._lock blocks the event loop for zero observable time on the happy path (no await inside the critical section). Trade-off: sync+async exclusion > minor event-loop contention under high contention (zero under normal traffic). Closes the silent self._state write race that could let a thread observe a half-updated breaker state — under a tight async loop with one stray sync caller this manifests as flaky breaker.call returns (one path thinks the breaker is open, the other thinks it's half-open).

Added

• tests/test_circuit_breaker_branches.py — 10 new branch tests for DEF-CB-LOCK-UNIFICATION-2026-09-12 (77bf38b): covers both the sync and async breaker.call paths through a single threading.Lock (state transitions, failure-count accumulation, half-open probe, open→closed reset on success, async-context contention with the same shared lock). Pins that no future refactor can re-introduce a separate _async_lock without tripping these tests.

Verification

Check	Result
ruff check src tests	All checks passed
mypy src/nullrun	Success: no issues found in 37 source files
pytest -q	1807 passed, 4 skipped in ~107s (vs 1797 baseline at 0.16.8 — 10 new tests from DEF-CB-LOCK-UNIFICATION-2026-09-12 circuit-breaker branch coverage)
Scratch diff	clean (dist_local/, *.defect* absent)
nullrun.__version__	0.17.0
Wire-format compatibility	unchanged from 0.16.8 (byte-identical /gate, /execute, /track, /cancel payloads)

Commits included

945a210 docs(changelog): add DEF-CB-LOCK-UNIFICATION-2026-09-12 to 0.17.0 block
77bf38b fix(sdk): unify circuit breaker lock — use sync Lock for both paths
2756862 chore(release): 0.17.0 — chain setter Token discipline + gate-cache staleness closure + lazy-export repair (#101)

[codecov]

Codecov Report

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