A dispatcher SIGKILLed between _call_spawn_fn and _set_worker_pid leaves a
live worker on a run with worker_pid NULL. release_stale_claims only extends
an expired claim for a recorded live pid, so on TTL expiry it reclaimed the
card and spawned a second worker beside the first: double billing, double
side effects, and a board showing one clean completed run (the first
worker's kanban_complete is refused as stale). Main CI hit it in
test_dispatcher_sigkill_mid_tick_never_destroys_or_duplicates_cards.
The worker now records its own pid on its run before the first model call
(adopt_worker_pid, worker_registered event, host-local claims only) and
exits without working the card when its run was already reclaimed. The
reclaim UPDATE also compares worker_pid so a registration landing between
the stale-claim SELECT and the UPDATE keeps the claim.
Repro: temporary sleep between spawn and pid record + kill 0.2 s after the
spawned event + slow first model reply -> 4/4 red on main with the CI
signature, 8/8 green here.
Fixes#121556
63e44332f5