The regression test used a bare `from _wakeup_helpers import install_fake_registry`,
which raises ModuleNotFoundError under the repo test runner (rootdir = repo root,
tests is a package). pytest treats that as a COLLECTION error for the file, not a
failure — so the whole suite stayed green while this file's tests silently never
ran, leaving the backoff fix with zero effective coverage.
Use the package-qualified `from tests._wakeup_helpers import install_fake_registry`,
matching the four sibling bg_task_complete suites. Confirmed the import now
resolves from the repo root (the bare form fails).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
_drain_loop read process_registry.completion_queue directly under a bare
`except Exception: continue`. A registry missing that attribute raised
AttributeError that was swallowed and retried with no backoff — a
100%-CPU tight loop with no log line. The loop now reads the queue via
getattr(..., None) and backs off on the stop event when it is absent
(mirroring streaming.py), catches queue.Empty explicitly for the normal
idle path, and logs a warning + backs off (_DRAIN_STOP.wait(1.0)) on any
other queue error so a persistent fault can neither spin the CPU nor stay
invisible.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
