The cache-only compatibility path selected the matching cached agent,
checked stream liveness under STREAMS_LOCK, released the lock, and only
then called agent.steer(). A Stop running in that gap published
phase='cancelling' and detached STREAMS/AGENT_INSTANCES while the
earlier Steer still enqueued into the cached worker, so the HTTP
response reported accepted guidance that cancellation already owned.
Revalidate stream membership, owner, and active-run
session/backend/phase and call agent.steer() under the same
STREAMS_LOCK -> ACTIVE_RUNS_LOCK edge Stop uses; interrupt,
persistence, and HTTP writes stay outside the lock. Cache eviction and
agent closing remain absent.
Extend tests/test_steer_cancel_ordering.py with a cache-only reverse-
order test (AGENT_INSTANCES absent, matching cached worker, decoy cache
entry) gating both unlocked edges around the stream-lock reacquire.
Stop-first must return stream_dead without calling agent.steer(); the
selected cache object is asserted to be the intended worker. Proven
red on the pre-fix code (order ['cancel','steer']) and green after.
Anthony Ruiz
84d66fe45f