Discord report (netti93): downloaded album tracks were tagged with
TRCK = "6/0" instead of "6/13" when source data was incomplete. The
retag tool wrote correct "6/13" because core/tag_writer.py already
handled the case.
Trace: core/metadata/enrichment.py:105 formatted unconditionally as
f"{track_number}/{total_tracks}" and many album-dict construction
sites pass total_tracks: 0 (per types.py, 0 means "unknown" — not a
real count). That 0 propagated straight to disk.
Fix at the consumer boundary so every album-dict constructor stays
unchanged. Lifted to pure helper
core/metadata/track_number_format.py:format_track_number_tag that
drops the /N suffix when total is 0 / None / negative — emits just
"6" instead. Matches retag's behavior + ID3 spec convention (TRCK
can be "N" or "N/M"). MP4 trkn tuple gets the same treatment via
format_track_number_tuple returning (6, 0) per spec's "unknown
total" marker.
Wired into all three format-write sites in enrichment.py: ID3 (TRCK),
Vorbis (tracknumber), MP4 (trkn). When source data has correct
total_tracks (album downloads via the metadata-source pipeline,
retag flow), behavior unchanged — still writes "6/13".
16 boundary tests pin every shape: known total / zero total / none
total / none track / zero track / negative inputs / string coercion
/ unparseable strings / floats truncate.
Full suite: 3113 passed.
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