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Bug: engine-toggle-prime-marker-registration-races-removal #944
Description
Activity
Restoring sections dropped by the promotion tooling.
Suspected Cause / Notes
StartPrimeIfNeededholds_primeGatewhile it registers, butCompletePrimeremoves the marker without taking the gate. Registration (line ~276) happens after the continuation is scheduled, so a continuation that finishes quickly can remove the marker (line ~348) before it is written. No current test fails on this. #942 fixes a different ordering (log before removal) and leaves this one out of scope by design. First recorded as NB-2 in the #735 code review.Source:
docs/features/active/2026-09-29-engine-toggle-prime-fault-logging-test-races-942/research/2026-09-29T23-20-engine-toggle-prime-fault-race-research.md, conclusion 3.Proposed Fix / Validation Ideas
- Write a deterministic regression test: use a pre-faulted
EngineActiveAsyncand assert that a secondGetPressedstarts a new prime. It must fail before the fix. - Fix options: register a placeholder before scheduling, or make removal conditional on the stored task being the completing one (
TryRemovewith aKeyValuePaircomparison), or take_primeGateinCompletePrime. - Use no sleeps, retries,
[DoNotParallelize]or Workers=1. - Sequence this after Bug: engine-toggle-prime-fault-logging-test-races #942 merges, because both change
CompletePrime.
- Write a deterministic regression test: use a pre-faulted
Delivered by PR 954 (merge commit 829ad41), parallel run bugs-2026-09-28. All 18 acceptance criteria in spec.md are checked off; all seven checks green on head f12b8d3 (run 36738150094) before merge. The approved one-time P3-T8 restart passed 7327 of 7327. Follow-ups are filed separately by the run coordinator.
Summary
In
EngineToggleStateCoordinator, a prime that completes synchronously in a non-success state can runCompletePrime's marker removal beforeStartPrimeIfNeededregisters that marker. A stale marker for a finished prime is then left in_primeTasks, which blocks any later re-prime for that engine. This is hazard B from the #942 research, first recorded as NB-2 in the #735 code review, and never promoted.Environment
GetPressed_WhenPrimeFaults_LogsErrorAndStillReturnsFalse)Steps to Reproduce
EngineActiveAsyncto return an already-faulted task, for example after a cached configuration-load fault.GetPressedfor that engine, which triggersStartPrimeIfNeeded.StartObservedPrimeschedules the continuation. The continuation can runCompletePrime(_primeTasks.TryRemove, line ~348) before the assignment_primeTasks[engineName] = ...at line ~276 stores it.Expected Behavior
A finished prime never leaves a marker in
_primeTasks, so a laterGetPressedcan start a fresh prime.Actual Behavior
The removal can precede the registration. The marker for the completed prime then stays registered,
ContainsKeyreturns true, and no later prime starts for that engine.Logs / Screenshots
docs/features/active/2026-09-29-engine-toggle-prime-fault-logging-test-races-942/research/2026-09-29T23-20-engine-toggle-prime-fault-race-research.md, conclusion 3.Impact / Severity
Source
From: docs/features/potential/2026-09-30-engine-toggle-prime-marker-registration-races-removal.md