The job was doing a blind fuzzy search for every low-quality track, ignoring that
enrichment writes each track's ISRC + per-source IDs into the file tags. Now it
reads the file's embedded ISRC and resolves the EXACT track via each source's
'isrc:' search (universal cross-source key), guarded by an ISRC-equality check so
a source that ignores the syntax can't produce a false match — exact track, exact
album context, one call. Falls back to the name/artist fuzzy search only for
un-enriched tracks with no usable ISRC. Findings record matched_via=isrc|search.
4 new seam tests (guard accept/reject, ISRC-preferred-over-fuzzy, fuzzy fallback).
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