[thatsrue]

What changed

combobulator combine <session> (the glob path, with no explicit VTT list) now raises CombineError naming every VTT left by a run that failed or was interrupted, and writes nothing. The new pipeline_cache.is_vtt_unfinished decides from the VTT's folder alone: the track is refused when the folder holds a chunk checkpoint (<stem>_progress.jsonl), or a current-version (3) manifest without a vtt record naming the VTT. A folder with no manifest, or a manifest from an older cache version, predates these records and is combined as before, unchecked. Batch runs are unchanged: they pass the exact VTTs they produced. AGENTS.md (the "Partial transcription is a failure" invariant) says how both kinds of session behave.

Why

When some chunks fail, whisper still writes the track's VTT and only process_file raises, after the write. A manual combine, which session-env tells the owner to run after editing labels, globbed every *.vtt and merged that transcript with gaps without an error.

Review follow-up: the first version required a vtt record, so it also refused sessions made before cache version 3 (no manifest, or a version 1 or 2 manifest), which finished but have no such record. Version 3 brought both the per-stage records and the chunk checkpoint (407b74e), and every finished version 3 run writes the vtt record, so those marks tell a failed or interrupted run apart from an old session. No override flag is added: with the old-session case handled, a refused track is one whose run really did not finish, and rerunning it is the fix.

Left out: the stale-sibling scenario (two folders matching one username, e.g. 3-cadderly and 7-cadderly, both match as whole tokens). A manual combine merges both. Refusing that would also refuse a session that really has two tracks for one speaker, which batch runs accept, so it needs a decision on whether two tracks per username are supported. It is not changed here. The check also cannot compare fingerprints with the current config, because a manual combine has no input audio, and a version 3 session folder moved to another path is refused because the record names absolute paths.

Closes #74

How you checked it

• test_glob_refuses_a_track_whose_run_did_not_finish (tests/test_combine.py), interrupted and failed-chunk cases: both fail with combine.py from main, pass with the fix.

• test_glob_combines_a_track_from_before_stage_records, no manifest and a version 2 manifest: both fail on the previous head of this branch, pass now.

• make lint, make typecheck, make test-fast (300 passed, 9 deselected): exit 0.

• CI's python -m build not run locally: build is not installed in the venv; the change touches no packaging.

• Slow inference tests not run: the change is in combine only, outside the audio pipeline.

• A bug fix comes with a test that fails without it

• Docs match how it works now

• No secrets or private information

[thatsrue]

Not ready to merge. The fresh review found that combine now refuses sessions with a manifest but no vtt record, including older sessions made before this check. It needs to tell an old session apart from a failed or interrupted run, or offer an explicit override, and AGENTS.md needs to say how old sessions behave.