Independent review showed the retry version was a scheduling lottery: under a
forced consumer-first schedule (provider generator held at the terminal chunk
until the consumer took it) both tests failed after 12 attempts with correct
production code. The reviewer also demonstrated the deterministic alternative;
this adopts it. At the chosen chunk the hook releases the finalizer and pumps
the stream's OWN event loop (stream._loop.run_until_complete over a
to_thread wait) until the finalizer has completed, then hands the chunk to the
consumer: a real happens-before on every schedule. A schedule probe's gate on
the provider generator is released first so the pump can reach EOF. The retry
helper and the race-forced plumbing are gone; each test runs once.
Adverse consumer-first schedule (reviewer's probe plugin): 3/3 pass (was 0/3).
Normal schedule: 6/6. Production fix 74de0fd4fe reverted: tool-call test still
fails, so the guard is intact.
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