v0.20.3: one artist spelled two ways

The sync was fine. Everything it put on the Rabbit was there and correct --
2,432 media files, 208 covers, a manifest whose every field type-checks
against the parser -- and andTunes still answered "No library / Couldn't read
library.json". Fifteen tracks took all 2,439 songs down with them.

Library.group() keyed albumsByKey case-folded and artistsByName raw-case, and
only ever built the Artist inside `if (album == null)`. So the second track of
an album whose artist is spelled differently found the album already there,
skipped the block that would have made the artist, and dereferenced the null
that came back. Six artists in trav's library are spelled two ways: RJD2/Rjd2,
Toro Y Moi/Toro y Moi, FatBoy Slim/Fatboy Slim, LOVING/Loving, Land Of The
Loops/Land of the Loops, Salami Rose Joe Louis/salami rose joe louis. It had
worked until the 12th because that sync was the first to carry both spellings
of one of those albums.

Both maps fold case now, and the artist is fetched-or-made before the album
block and held, so no lookup left in group() can come back null. Artist gains
a key the way Album always had one, and ListActivity navigates by it --
ALBUM_ROW already passed album.key, so artists just stopped being the
exception.

The device filesystem is case-insensitive, so those two spellings are one
folder there. plan_andtunes_sync compared exact strings and saw every such
file as stale *and* missing, deleting and re-copying it over MTP on every
sync forever; the diff and the collision rule both fold now. plan.stale still
carries the device's own spelling, since that is what _delete_stale unlinks by.

Verified on the Rabbit: 2,439 songs listed, RJD2 one row of 12 songs.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01SKXUgsBBwe3qaHEjeV8ubP

scripts/make_dev_library.py

@@ -26,6 +26,9 @@ The edge cases here are not decoration. Each one has bitten something:
 * a multi-disc release                               → the "2-04" prefix;
 * a compilation whose album_artist differs           → album grouping and
                                                        album art keying;
+* one artist spelled two ways on one album           → the case-folded
+  ("RJD2" / "Rjd2")                                    grouping in the app and
+                                                       the folded device diff;
 * a dangling location                                → the "skipped" counters;
 * a 200-character title                              → the 150-char truncation;
 * non-ASCII and an emoji                             → UTF-8 all the way to
@@ -152,6 +155,10 @@ EDGE_TRACKS = [
     ("Song", "Twin Records", "Doubles", ".mp3", "collision A"),
     ("Song", "Twin Records", "Doubles", ".mp3", "collision B"),
     ("Orphan Take", "", "", ".mp3", "no artist, no album"),
+    ("Iced Lightning", "RJD2", "Since We Last Spoke", ".mp3",
+     "one artist spelled two ways, sharing an album"),
+    ("Making Days Longer", "Rjd2", "Since We Last Spoke", ".mp3",
+     "the other spelling — the pair is the point"),
     ("わたしの音楽 🎧", "Sakura Denwa", "東京の夜", ".mp3", "non-ASCII + emoji"),
     ("A Title That Simply Refuses To Stop Going On And On " * 4, "Verbose",
      "Excess", ".mp3", "200+ characters, hits the 150-char truncation"),