Tower worker now persists faster-whisper's segment-level output
(start/end/text + word-level timing when available) alongside the
existing joined `transcript_text`. The text column stays the canonical
input the extractor reads — this is additive.
Changes:
- alembic v4: sources.transcript_segments JSONB NULL. JSONB rather than
JSON so future equality/containment queries are indexable without a
re-migration. Same lovebug-no-CREATE-on-petalbrain guard as prior
migrations.
- ORM model: Optional[list] mapped to JSONB (postgresql dialect).
- transcribe.py:
- Always pass word_timestamps=True to faster-whisper.transcribe.
- New segment_to_dict() flattens the upstream NamedTuple-shaped
Segment/Word into JSON-safe plain dicts so the JSONB write doesn't
drag faster-whisper into any reader.
- Per-word defensive conversion: a single malformed word can't drop
the surrounding segment.
- transcribe_worker._advance: after a successful transcribe, persist
segments into source.transcript_segments inside a try/except. If the
JSONB write fails (oversize row, malformed dict, etc.) we log a
warning and still commit transcript_text + status=TRANSCRIBED — the
pipeline never crashes over the additive index.
- Tests: three new unit tests against fake Segment/Word objects cover
the happy path (word entries serialise), the no-words case
(`segment.words is None` → empty list), and the malformed-word skip.
json.dumps(d) asserts JSONB-binding compatibility.
Live-verified: migration applied clean against petalbrain (`\d sources`
shows transcript_segments jsonb); ORM round-trip writes and reads the
sample payload identically. GPU large-v3 word-timestamp behaviour is
unchanged from upstream — only the tower can validate that hot path.
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