fix(worker): canonicalize bonus-track filenames past the MB tracklist

A track beyond the MusicBrainz tracklist (a Qobuz bonus track) kept streamrip's
raw name (e.g. "13. John Mayer - St. Patrick's Day (Album Version).flac") while
the main tracklist got clean "## Title" names. plan_track_names now canonicalizes
such extras: strip the leading track-number prefix and a leading "<artist> - ",
yielding "13 St. Patrick's Day (Album Version).flac". Requires an explicit
delimiter after the number so titles like "99 Luftballons" are left alone; with
no tracklist resolved at all the on-disk stem is still kept.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

worker/lyra_worker/_mutagen.py

@@ -1,21 +1,48 @@
 import os
+import re
 
 from lyra_worker.library import safe_name
 
 _AUDIO_EXT = {".flac", ".mp3", ".m4a", ".opus", ".ogg", ".aac", ".wav"}
 
+# Leading "13.", "13 -", "13)" style track-number prefix streamrip bakes into a bonus-track
+# filename. Requires an explicit delimiter so a real title that merely starts with a number
+# (e.g. "99 Luftballons") is left alone.
+_NUM_PREFIX = re.compile(r"^\s*\d+\s*[.):\-]\s*")
 
-def plan_track_names(names: list[str], tracklist: tuple[str, ...]) -> list[tuple[str, str, str, int]]:
+
+def _clean_extra_title(stem: str, artist: str = "") -> str:
+    """Derive a display title for a track BEYOND the MusicBrainz tracklist (a bonus track that
+    streamrip named itself, e.g. `13. John Mayer - St. Patrick's Day (Album Version)`). Strip a
+    leading track-number prefix, then a leading `<artist> - ` if present, so the example yields
+    `St. Patrick's Day (Album Version)`. Falls back to the stem if nothing strips."""
+    s = _NUM_PREFIX.sub("", stem).strip()
+    if artist:
+        s = re.sub(r"^" + re.escape(artist) + r"\s*-\s*", "", s, flags=re.IGNORECASE).strip()
+    return s or stem
+
+
+def plan_track_names(
+    names: list[str], tracklist: tuple[str, ...], artist: str = ""
+) -> list[tuple[str, str, str, int]]:
     """Map audio filenames -> (old_name, new_name, title, track_number).
 
-    Files are sorted; titles come from `tracklist` by position when available,
-    else the filename stem. Pure — no filesystem or tag I/O.
+    Files are sorted; titles come from `tracklist` by position when available. A file BEYOND
+    the tracklist (a bonus track streamrip named itself) is canonicalized via `_clean_extra_title`
+    so it gets a clean `## Title.ext` name too; with no tracklist at all the on-disk stem is kept.
+    Pure — no filesystem or tag I/O.
     """
     plan: list[tuple[str, str, str, int]] = []
     audio = sorted(n for n in names if os.path.splitext(n)[1].lower() in _AUDIO_EXT)
     for i, name in enumerate(audio):
         ext = os.path.splitext(name)[1].lower()
-        title = tracklist[i] if i < len(tracklist) else os.path.splitext(name)[0]
+        stem = os.path.splitext(name)[0]
+        if i < len(tracklist):
+            title = tracklist[i]
+        elif tracklist:  # a genuine bonus track past a known tracklist -> canonicalize its name
+            title = _clean_extra_title(stem, artist)
+        else:  # no tracklist resolved at all -> keep the on-disk stem (renumbered)
+            title = stem
         new_name = f"{i + 1:02d} {safe_name(title)}{ext}"
         plan.append((name, new_name, title, i + 1))
     return plan
@@ -29,7 +56,7 @@ class MutagenTagger:
         import mutagen
 
         names = os.listdir(album_dir)
-        for old_name, new_name, title, number in plan_track_names(names, target.tracklist):
+        for old_name, new_name, title, number in plan_track_names(names, target.tracklist, target.artist):
             try:
                 path = os.path.join(album_dir, old_name)
                 audio = mutagen.File(path, easy=True)

worker/tests/test_mutagen.py

@@ -1,4 +1,34 @@
-from lyra_worker._mutagen import plan_track_names
+from lyra_worker._mutagen import _clean_extra_title, plan_track_names
+
+
+def test_clean_extra_title_strips_number_and_artist_prefix():
+    assert _clean_extra_title(
+        "13. John Mayer - St. Patrick's Day (Album Version)", "John Mayer"
+    ) == "St. Patrick's Day (Album Version)"
+
+
+def test_clean_extra_title_strips_number_without_artist_prefix():
+    assert _clean_extra_title("13. St. Patrick's Day", "John Mayer") == "St. Patrick's Day"
+
+
+def test_clean_extra_title_leaves_plain_title_and_numeric_titles():
+    assert _clean_extra_title("Hidden Track", "John Mayer") == "Hidden Track"
+    # "99 Luftballons" has no delimiter after the number -> not a track-number prefix
+    assert _clean_extra_title("99 Luftballons", "Nena") == "99 Luftballons"
+
+
+def test_plan_canonicalizes_bonus_track_beyond_tracklist():
+    names = [f"{i:02d} Track{i}.flac" for i in range(1, 13)] + [
+        "13. John Mayer - St. Patrick's Day (Album Version).flac"
+    ]
+    tracklist = tuple(f"Track{i}" for i in range(1, 13))
+    plan = plan_track_names(names, tracklist, artist="John Mayer")
+    assert plan[12] == (
+        "13. John Mayer - St. Patrick's Day (Album Version).flac",
+        "13 St. Patrick's Day (Album Version).flac",
+        "St. Patrick's Day (Album Version)",
+        13,
+    )
 
 
 def test_plan_uses_tracklist_titles_and_numbers():