The session permit's rule that a retryable error does not raise the sweep's
stop was unpinned: the existing retryable test uses a pool of two, so both
sessions spawn before either fails, and `held.stop = outcome.is_err()`
survived. Under a pool of one the second entry is spawned only after the
first session's permit is released; the first call faults as retryable and
the second session must still run and commit in the same sweep.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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