Flag slave-only songs whose album or artist the master has

Scans now mark slave-only songs as missing from the master when the master
has their album folder or at least their artist folder. A new Missing from
master filter in Review lists them, split by album and artist.

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

internal/engine/missing_test.go

@@ -0,0 +1,64 @@
+package engine
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/cdnutter/playlink/internal/store"
+)
+
+func TestMissingFromMaster(t *testing.T) {
+	ev := setup(t, false)
+	m, s := ev.master, ev.slave
+	ev.write(m, "Caravan Palace/Robot Face/01 Lone Digger.flac", "a")
+	ev.write(m, "Caravan Palace/Chronologic/Disc 1/01 Miracle.flac", "b")
+	ev.write(s, "Caravan Palace/Robot Face/01 Lone Digger.flac", "a")
+	ev.write(s, "Caravan Palace/Robot Face/05 Waterguns.mp3", "song")              // album in master
+	ev.write(s, "Caravan Palace/robot face (Deluxe Edition)/12 Bonus.mp3", "song") // same album, other spelling
+	ev.write(s, "Caravan Palace/Chronologic/Disc 2/03 Plume.mp3", "song")          // disc folders ignored
+	ev.write(s, "Caravan Palace/Panic/01 Dragons.mp3", "song")                     // only the artist
+	ev.write(s, "Caravan Palace/Loose.mp3", "song")                                // only the artist
+	ev.write(s, "Unknown Artist/Album/Song.mp3", "song")                           // neither
+	ev.scan()
+
+	want := map[string]string{
+		"Caravan Palace/Robot Face/05 Waterguns.mp3":              "album",
+		"Caravan Palace/robot face (Deluxe Edition)/12 Bonus.mp3": "album",
+		"Caravan Palace/Chronologic/Disc 2/03 Plume.mp3":          "album",
+		"Caravan Palace/Panic/01 Dragons.mp3":                     "artist",
+		"Caravan Palace/Loose.mp3":                                "artist",
+		"Unknown Artist/Album/Song.mp3":                           "",
+		"Caravan Palace/Robot Face/01 Lone Digger.flac":           "",
+	}
+	for rel, level := range want {
+		mt, err := ev.st.MatchBySlave(ctx, ev.pair.ID, rel)
+		if err != nil {
+			t.Fatal(rel, err)
+		}
+		if mt.Missing != level {
+			t.Errorf("%s: missing %q, want %q", rel, mt.Missing, level)
+		}
+	}
+	mt, _ := ev.st.MatchBySlave(ctx, ev.pair.ID, "Caravan Palace/Chronologic/Disc 2/03 Plume.mp3")
+	if !strings.Contains(mt.Reason, `"Caravan Palace/Chronologic"`) {
+		t.Errorf("reason should name the master's album folder: %q", mt.Reason)
+	}
+
+	sum, err := ev.st.Summary(ctx, ev.pair.ID)
+	if err != nil || sum.Missing["album"] != 3 || sum.Missing["artist"] != 2 {
+		t.Fatalf("summary %+v %v", sum.Missing, err)
+	}
+	if _, n, _ := ev.st.Matches(ctx, ev.pair.ID, store.MatchFilter{Status: "missing"}); n != 5 {
+		t.Fatalf("missing filter: %d", n)
+	}
+	if _, n, _ := ev.st.Matches(ctx, ev.pair.ID, store.MatchFilter{Status: "missing_album"}); n != 3 {
+		t.Fatalf("missing_album filter: %d", n)
+	}
+
+	// Once the master gets the song, it is no longer missing.
+	ev.write(m, "Caravan Palace/Robot Face/05 Waterguns.mp3", "song")
+	ev.scan()
+	if mt, _ := ev.st.MatchBySlave(ctx, ev.pair.ID, "Caravan Palace/Robot Face/05 Waterguns.mp3"); mt.Missing != "" || mt.Status == store.StatusUnmatched {
+		t.Fatalf("now in master: %+v", mt)
+	}
+}