When a worker calls ``kanban_block(reason="review-required: ...")`` to
hand a task off for human review, the dispatcher's ``recompute_ready``
was treating the resulting ``blocked`` status as eligible for
auto-promotion — exactly the same as a circuit-breaker block. On the
next tick the task flipped back to ``ready``, a fresh worker spawned,
found nothing to do (work already applied, review-required comment
already posted), exited cleanly, got recorded as ``protocol_violation``
→ ``gave_up`` → ``blocked``, and the dispatcher promoted again.
Infinite loop until manual ``hermes kanban reclaim`` + ``kanban block``.
Add ``_has_sticky_block`` which distinguishes the two block sources
using the cheapest available signal: the most recent
``"blocked"``/``"unblocked"`` event in ``task_events``.
* Worker / operator ``kanban_block`` emits ``"blocked"`` →
``_has_sticky_block`` returns True → ``recompute_ready`` skips the
task entirely. ``unblock_task`` emits ``"unblocked"`` which flips
the predicate back, so the only legitimate exit is the documented
human-in-the-loop path.
* Circuit-breaker ``_record_task_failure`` emits ``"gave_up"`` (not
``"blocked"``) → predicate stays False → original
parent-completion-recovery semantics from #40c1decb3 are preserved.
* Tasks blocked purely by direct DB manipulation also recover, since
they have no ``"blocked"`` event row at all — matches the existing
``test_recompute_ready_promotes_blocked_with_done_parents`` fixture
behaviour.
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