GatewayStreamConsumer.run() processed queued deltas in an infinite loop
with no check on whether the session was still current. On /new or /stop
mid-stream, the consumer kept editing and delivering stale response
fragments alongside the 'Session reset!' ack.
PR #11016 (b7bdf32d) fixed the runner side via sentinel promotion/release
but left the stream consumer unguarded. Every other async callback in
run.py already bails via _run_still_current(); the stream consumer was
the only one missing it.
- stream_consumer.py: optional run_still_current callback, checked at the
top of the run() loop; returns early when the session is stale.
- run.py: pass the existing _run_still_current closure at both call sites
(proxy path and agent path).
- tests: TestRunStillCurrentGuard — immediate staleness, mid-stream
staleness, always-current, no-callback default, pending-finish.
Co-authored-by: jasonQin6 <39369769+jasonQin6@users.noreply.github.com>
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