state.db is canonical. The 'use whichever source is longer' branch was
defensive code for the pre-DB migration; on every real DB it has not
fired (verified on a session corpus with 27 jsonl files / 950 sessions —
zero jsonl-bigger cases).
Test changes:
- TestLoadTranscriptCorruptLines: deleted (tested dead JSONL code path)
- TestLoadTranscriptPreferLongerSource: deleted (tested removed fallback)
- Replaced with TestLoadTranscriptDBOnly (DB-only reads)
- TestSessionStoreRewriteTranscript: fixture now creates DB session
- test_gateway_retry_replaces_last_user_turn: fixture uses real DB
Add regression coverage for gateway and CLI /retry behavior so retried messages replace the original user turn instead of accumulating duplicate user entries in history.
