fix: same-titled albums of two release groups are two albums, and a missing track with no disc is on disc 1

The scanner found an album by artist and title alone, so Weezer's six
self-titled albums (1994–2026) were one 118-track row and their merges,
wants and upgrades counted them as one. A same-named row whose release group
is known and differs from the file's is now another album; tagReadVersion 7
re-reads the library so existing tracks move to their own rows.

WantHoldings compared discs with IS NOT DISTINCT FROM, so a missing track 6
with no disc was never covered by a present disc 1 track 6. Air's Love 2
stayed wanted and was downloaded again for nothing.

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

internal/wanted/upgrade_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/jackc/pgx/v5/pgtype"
 	"github.com/jackc/pgx/v5/pgxpool"
 
 	"git.fabledsword.com/bvandeusen/minstrel/internal/db/dbq"
@@ -135,3 +136,39 @@ func TestCheckUpgrades_ARipIsReplacedWhateverTheSetting_Integration(t *testing.T
 		t.Errorf("a rip: upgrade %q", w.Upgrade)
 	}
 }
+
+// A missing track with no disc number is on disc 1, so a present 1/2 stands in
+// for a missing "2". Air's Love 2 stayed wanted over one such row and was
+// downloaded again for nothing (2026-10-20). A missing track no present track
+// covers still counts.
+func TestWantHoldings_AMissingTrackWithNoDiscIsOnDiscOne_Integration(t *testing.T) {
+	pool := newPool(t)
+	ctx := context.Background()
+	album := seedMP3s(t, pool, 320, false)
+	if _, err := pool.Exec(ctx, `UPDATE tracks SET disc_number = 1 WHERE album_id = $1`, album.ID); err != nil {
+		t.Fatal(err)
+	}
+	q := dbq.New(pool)
+	for _, n := range []int32{2, 3} {
+		num := n
+		tr, err := q.UpsertTrack(ctx, dbq.UpsertTrackParams{
+			Title: fmt.Sprintf("Stale %d", n), AlbumID: album.ID, ArtistID: album.ArtistID, TrackNumber: &num,
+			DurationMs: 200000, FilePath: fmt.Sprintf("/music/ballad/stale-%d.mp3", n), FileSize: 1, FileFormat: "mp3",
+		})
+		if err != nil {
+			t.Fatal(err)
+		}
+		if _, err := pool.Exec(ctx, `UPDATE tracks SET missing_since = now() - interval '2 days' WHERE id = $1`, tr.ID); err != nil {
+			t.Fatal(err)
+		}
+	}
+	rows, err := q.WantHoldings(ctx, dbq.WantHoldingsParams{
+		Since: pgtype.Timestamptz{Time: time.Now(), Valid: true}, GroupMbid: theBallad, AlbumID: album.ID,
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	if len(rows) != 1 || rows[0].UncoveredMissing != 1 {
+		t.Fatalf("holdings = %+v, want one album with 1 uncovered missing track (track 3 only)", rows)
+	}
+}