fix(tasks): prevent duplicate dispatch on requeue race#3963
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When a task was re-queued, callers enqueued it before sending EventTypeRequeued. If EventTypeEmpty was already waiting in queueEvents (the 5s ticker), handleQueue could ClaimAndDequeue the task while it still occupied the running/active sets and spawn a duplicate dispatch. Move enqueue into the EventTypeRequeued handler so it runs only after onTaskStop releases pool bookkeeping. Add a regression test for the concurrent Empty+Requeued ordering. Co-authored-by: Denis Gukov <fiftin@outlook.com>
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Bug and impact
When a remote task was re-queued (runner offline, dispatch lost, or all runners busy), callers enqueued it before emitting
EventTypeRequeued. If anEventTypeEmptytick was already waiting inqueueEvents,handleQueuecould process that tick first,ClaimAndDequeuethe task while it still occupied the running/active sets, and spawn a duplicate dispatch — potentially running the same playbook twice (including on different runners).Root cause
Re-queue paths called
state.Enqueue()synchronously, then sentEventTypeRequeuedto an unbuffered/buffered channel.handleQueueprocesses events in FIFO order, so a queuedEventTypeEmptycould run between enqueue andonTaskStop, violating the invariant that only waiting, non-running tasks enter the claim loop.Fix
Enqueueinto theEventTypeRequeuedhandler, afteronTaskStopreleases running/active/claim state.TaskRunner.run(all runners busy) and both reconciler requeue helpers.dispatchQueueEventfor testability.TestTaskPool_RequeuedEventNotClaimedByConcurrentEmptyPass.Validation
go test ./services/tasks/... -short