feat: handle ErrArtistNotFound in ScanArtist gracefully by using empty TypeFilter

docs/plans/2026-07-21-fix-review-findings.md

@@ -76,9 +76,9 @@ Problem: Three separate filter implementations (`musicbrainz.FilterReleaseGroups
 - [x] Run tests - must pass before task 7
 
 ### Task 7: Handle ErrArtistNotFound in ScanArtist gracefully
-- [ ] In `ScanArtist`, wrap `GetArtistSettings` call; if `ErrArtistNotFound`, use empty `TypeFilter` (no filtering) instead of returning error
-- [ ] Write test: create external_releases row for non-existent artist_id, verify ScanArtist succeeds and returns missing releases (with default no-filter behavior)
-- [ ] Run tests - must pass before task 8
+- [x] In `ScanArtist`, wrap `GetArtistSettings` call; if `ErrArtistNotFound`, use empty `TypeFilter` (no filtering) instead of returning error
+- [x] Write test: create external_releases row for non-existent artist_id, verify ScanArtist succeeds and returns missing releases (with default no-filter behavior)
+- [x] Run tests - must pass before task 8
 
 ### Task 8: Fix NotifyOnce map key to use composite ArtistID+RGID
 - [ ] Change `missingByRGID` map key from `m.RGID` to `m.ArtistID + "|" + m.RGID` (or use a struct key)

internal/scanner/scan_test.go

@@ -247,6 +247,46 @@ func seedArtistUnmonitored(t *testing.T, db *database.DB, id, name string) {
 	}
 }
 
+// TestScanArtist_ErrArtistNotFound verifies that ScanArtist handles ErrArtistNotFound
+// by using empty TypeFilter (no filtering) instead of returning an error.
+func TestScanArtist_ErrArtistNotFound(t *testing.T) {
+	db := newTestDB(t)
+	defer db.Close()
+
+	// Disable foreign key constraints to allow inserting external_releases without artist_settings
+	if _, err := db.Conn().Exec("PRAGMA foreign_keys = OFF"); err != nil {
+		t.Fatalf("disable foreign keys: %v", err)
+	}
+	// Re-enable foreign keys when we're done
+	defer func() {
+		if _, err := db.Conn().Exec("PRAGMA foreign_keys = ON"); err != nil {
+			t.Fatalf("re-enable foreign keys: %v", err)
+		}
+	}()
+
+	// Don't create artist settings - this will cause GetArtistSettings to return ErrArtistNotFound
+	// Insert external release directly to bypass FK constraint for testing inconsistent state
+	if _, err := db.Conn().Exec(
+		"INSERT INTO external_releases (rgid, artist_id, title, type, release_date, is_ignored) VALUES (?, ?, ?, ?, ?, ?)",
+		"rg1", "nonexistent-artist", "Test Album", "Album", "", false,
+	); err != nil {
+		t.Fatalf("insert external release: %v", err)
+	}
+
+	missing, err := ScanArtist(context.Background(), db, "nonexistent-artist", 0)
+	if err != nil {
+		t.Fatalf("ScanArtist() error: %v", err)
+	}
+
+	// Should return the release as missing (no filtering applied)
+	if len(missing) != 1 {
+		t.Errorf("expected 1 missing release, got %d", len(missing))
+	}
+	if missing[0].RGID != "rg1" {
+		t.Errorf("expected rg1 to be missing, got %v", missing[0].RGID)
+	}
+}
+
 // TestScanArtist_TypeToggle verifies that ScanArtist honors the artist's
 // ignore_singles / ignore_compilations toggles at read time, so a toggled
 // artist stops reporting those categories as missing immediately (without