Register(taskId, cts) already refuses (and logs) a double-registration, but
both call sites discarded the bool and dispatched anyway under an
unregistered CTS. If the loser then unregistered the winner's CTS during
its own cleanup, TryCancel could silently no-op against a live process.
- OverrideSlotService.StartInSlot now fails RunNow/ContinueTask loudly
(throws) when it loses the registration race instead of registering
over — or silently proceeding despite losing to — the queue picker.
- QueueService's picker loop retries registration briefly (the loser's own
claim-attempt-then-unregister resolves fast) before dispatching; if
registration never resolves it marks the already-claimed row Failed
instead of running it unregistered.
- RunCancellationRegistry.Unregister already had compare-and-remove
semantics (TryRemove(KeyValuePair)), so a loser's cleanup could not have
removed the winner's CTS once registration correctly failed.
Added regression tests exercising the real registry through both dispatch
paths: RunNow losing the registration race throws without disturbing the
winner, the picker's retry succeeds and TryCancel reaches the live run when
the loser unregisters in time, and the picker fails the task instead of
running unregistered when it never does.
TaskRunner.RunAsync created the worktree (PrepareRunDirectoryAsync)
before claiming Running via StartRunningAsync. RunNow dispatches by
task id with no atomic claim of their own, so a Queued task racing
the queue picker's atomic SQL claim could hit WorktreeManager's
branch-collision self-heal, which force-removes and recreates the
winner's live worktree mid-run.
Move the claim before any resource creation and bail out immediately
when it's rejected. OverrideSlotService.RunNow also fast-rejects a
task already Running in the DB (defense in depth). RunCancellationRegistry
now refuses (and logs) a double registration instead of silently
overwriting the first CTS, so a losing dispatch's cleanup can no
longer unregister the winner's cancellation token.
mika kuns