The record_usage method performed an unprotected read-modify-write on
_daily_costs, a classic TOCTOU race condition. In multi-threaded execution
(ThreadPoolExecutor for parallel plan steps), two threads could interleave
their .get() read and = write, causing one thread's cost increment to be
silently overwritten by the other.
Changes:
- Add _daily_costs_lock: threading.Lock to CostTracker.__init__
- Wrap the read-modify-write in record_usage with self._daily_costs_lock
- Protect reads in check_daily_budget and get_daily_spend with the same lock
- Add Behave @concurrency scenario: 20 threads concurrently call record_usage;
final daily spend must equal the sum of all individual costs
- Add Robot Framework integration smoke test via helper_cost_controls.py
cost-tracker-concurrent command
All accesses to _daily_costs are now lock-protected. nox -e typecheck passes
with zero errors. Existing cost_controls tests continue to pass.
ISSUES CLOSED: #1919
freemo