Callers that join an in-flight fetch share one FetchResult. #499 released the
payload inside the delivery loop, so the first callback got the data and every
joiner got `result.data is None`.
That is not a quiet degradation. Consumers read `result.data.get('events')`, so
they raise AttributeError -- which the delivery loop catches and logs. The
entire failure surfaced as one line:
ERROR - src.background_data_service - Error in callback for request
nhl_2026_...: 'NoneType' object has no attribute 'get'
and a manager that silently never received its schedule. Seen on hardware:
NHLRecentManager logs "Background fetch completed for 2026: 1000 events" and
the very next line is the error, from NHLUpcomingManager's callback on the same
request -- which had already logged "No events found in shared data."
Deduplication is the normal case, not a corner. A sport's recent, upcoming and
live managers all want the same season schedule, so the second and third are
joiners on almost every cycle. _release_payload's own docstring said "once A
callback has been handed the data", singular, which is the assumption that
broke: the loop above it was written for many, and says so.
Moved after the loop, and guarded on `callbacks` being non-empty. The guard
matters: a request submitted without a callback must keep its payload, because
polling get_result() is then the only way to collect it. The per-delivery
release got that right by accident -- an empty list never entered the loop body
-- and the existing test for it caught the omission.
test_background_payload_release.py gains TestJoinersAllGetTheData: two
submitters on one in-flight cache_key, asserting both are handed a populated
payload, plus that the memory fix still happens once they have all had it.
test_background_fetch_dedupe.py already proved the joiner's callback FIRES; it
never checked what the callback received, which is the gap that let this
through.
Verified the new test bites: restoring the release inside the loop fails it
with "'second' was handed a released payload".
Full suite 3716 passed, 6 skipped.
Claude-Session: https://claude.ai/code/session_014RRtqXDCnvnY6EQwhT5CV9
Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>
