Documents the 5-phase investigation that uncovered 5 distinct bugs:
1. NameError on models.Metadata (missing import after de-cruft)
2. Mock sprint routing fragile to session_id chain
3. Mock epic branch only matched literal prompt
4. Mock worker session_id fallback leaked across tests
5. refresh_from_project task overwrote self.tracks with disk read
The final root cause (bug 5) was a production race condition where
the 'refresh_from_project' task replaced self.tracks with a disk
read that returned 0 tracks in batched test environments, losing
the in-memory tracks that were just appended by self.tracks.append(...).
Diagnostic techniques documented: code reading, file-based logging,
counter simulation, minimal test reproduction, and id() logging.
The id() logging was the breakthrough that proved the list was
being replaced.
Verified: 3 consecutive PASS runs of the failing test combination;
15 wider tests pass with no regressions.
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