fix(tasks,runners): critical runner/task requeue and finalization bugs

[cursor]

Summary

Cherry-picks validated fixes for three critical correctness bugs still present on develop. No new behavioral commits since yesterday's inspection (only CI/test skips: 75c98980, ab623b13, 48cb4741, fbebe1a1).

Bugs fixed

1. Duplicate dispatch on ErrAllRunnersBusy

Impact: When all runners are at capacity, a task requeued via ErrAllRunnersBusy was enqueued while still in the running set; EventTypeRequeued was deferred. A concurrent queue tick could ClaimAndDequeue the same task and start a second dispatch goroutine on the same TaskRunner.

Root cause: TaskRunner.run called state.Enqueue before releasing running/active bookkeeping.

Fix: Call onTaskStop before enqueue and emit EventTypeRequeued synchronously (matching reconciler requeue paths).

2. Runner client overwrites stopped → failed on terminated_jobs

Impact: When the server returns terminated_jobs and emergency-stops a job, Run() unwinds with an error. The error path overwrote an already-terminal stopped status with failed, misreporting task outcome to the server.

Root cause: Unconditional failure status assignment in job_pool.go after Run() error.

Fix: Add finalizeAfterRun that respects an already-finished status.

3. HA pool state leak in failTaskRunnerLost

Impact: In HA mode, when the reconciler wins the finalize lock but the DB already has a terminal status (e.g. runner reported success on another node), it returned early without completing finalization. Pool/Redis state (running set, claims, autorun children) leaked.

Root cause: Early return in failTaskRunnerLost when tsk.Task.Status.IsFinished() without calling finalizeRemoteTaskLocked. Also TaskPool.finalizeRemoteTaskLocked only checked End != nil under HA.

Fix: Complete finalization when DB already finished; harden offline requeue with pre-mutation DB re-check and rollback on persist failure; release stale pool state when End is already set (non-HA too).

Validation

• go test ./services/tasks/... ./services/runners/... — all pass
• New tests: TestTaskRunner_ErrAllRunnersBusy_ReleasesRunningBeforeEnqueue, TestRunningJob_finalizeAfterRun_*, reconciler HA finalization tests