fix: AcoustID decides any one-album mismatch the lengths cannot, not only copies each cut to its slot (#6169)

The first pass on the operator's library held 16 groups. In several, every
copy's own lookup names one recording (Wombats Record Shop/Tormentor,
Alchemist (2)/Prelude, Monday Chill 8/9, 404sessions), but one copy sits 3-10s
from its slot, so the every-copy-fits precondition kept AcoustID out. Now:
copies whose lookups all agree are that recording, whatever their
fingerprints read; copies of the same audio are asked about as before; and
the track list places the recording in one copy's slot, or none. Copies
filed as one song are not settled here.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/library/duplicate_classify_test.go

@@ -114,9 +114,9 @@ func TestWrongSlots(t *testing.T) {
 	}
 }
 
-// One recording cut to each of several slots' lengths (Savant's Mortals): the
-// lengths cannot place it, and what AcoustID calls it does (#6169).
-func TestTrimmedCopies(t *testing.T) {
+// The lengths cannot place a recording filed as several songs (Savant's
+// Mortals, cut to each slot's length); what AcoustID calls it can (#6169).
+func TestNamedCopies(t *testing.T) {
 	track := func(title string, ms int32, rec string) dbq.MbReleaseTrack {
 		return dbq.MbReleaseTrack{Title: title, LengthMs: ms, RecordingMbid: rec}
 	}
@@ -127,34 +127,27 @@ func TestTrimmedCopies(t *testing.T) {
 	album := []dbq.MbReleaseTrack{
 		track("Tormentor", 221000, "rec-tormentor"), track("Record Shop", 180000, "rec-record-shop"), track("Ice Cream", 200000, "rec-ice"),
 	}
-	if !trimmedToSlots(copies, album) {
-		t.Fatal("each copy fits its own slot: trimmedToSlots should hold the group")
-	}
-	if trimmedToSlots(copies[:1], album) {
-		t.Error("one title is not several songs' slots")
-	}
-	if trimmedToSlots([]slotCopy{copies[0], {Title: "Record Shop", Artist: "The Wombats", DurationMs: 220000}}, album) {
-		t.Error("a copy that does not fit its slot is wrongSlots' to decide")
-	}
 	cases := []struct {
 		name       string
+		copies     []slotCopy
 		tracks     []dbq.MbReleaseTrack
 		recordings []string
 		keep       int
 		losers     []int
 		ok         bool
 	}{
-		{"AcoustID names Tormentor", album, []string{"rec-tormentor"}, 0, []int{1}, true},
-		{"one of several candidates is on the album", album, []string{"rec-elsewhere", "rec-record-shop"}, 1, []int{0}, true},
-		{"AcoustID knows none", album, nil, -1, []int{0, 1}, true},
-		{"the recording is another song on the album", album, []string{"rec-ice"}, -1, []int{0, 1}, true},
-		{"candidates in both copies' slots", album, []string{"rec-tormentor", "rec-record-shop"}, -1, nil, false},
-		{"the track list names no recording for a slot", []dbq.MbReleaseTrack{
+		{"AcoustID names Tormentor", copies, album, []string{"rec-tormentor"}, 0, []int{1}, true},
+		{"one of several candidates is on the album", copies, album, []string{"rec-elsewhere", "rec-record-shop"}, 1, []int{0}, true},
+		{"AcoustID knows none", copies, album, nil, -1, []int{0, 1}, true},
+		{"the recording is another song on the album", copies, album, []string{"rec-ice"}, -1, []int{0, 1}, true},
+		{"candidates in both copies' slots", copies, album, []string{"rec-tormentor", "rec-record-shop"}, -1, nil, false},
+		{"the track list names no recording for a slot", copies, []dbq.MbReleaseTrack{
 			track("Tormentor", 221000, "rec-tormentor"), track("Record Shop", 180000, ""),
 		}, []string{"rec-tormentor"}, -1, nil, false},
+		{"every copy filed as the one song named", []slotCopy{copies[0], copies[0]}, album, []string{"rec-tormentor"}, -1, nil, false},
 	}
 	for _, tc := range cases {
-		keep, losers, ok := trimmedCopies(copies, tc.tracks, tc.recordings)
+		keep, losers, ok := namedCopies(tc.copies, tc.tracks, tc.recordings)
 		if keep != tc.keep || ok != tc.ok || fmt.Sprint(losers) != fmt.Sprint(tc.losers) {
 			t.Errorf("%s: got keep=%d losers=%v ok=%v, want keep=%d losers=%v ok=%v",
 				tc.name, keep, losers, ok, tc.keep, tc.losers, tc.ok)