fix: address fourth code review findings

- Fix FK constraint violation in SyncArtistDiscography: delete
  notifications_sent rows before external_releases to prevent
  constraint failure when re-syncing artists with prior notifications.
- Implement per-artist type filtering: FilterReleaseGroups now accepts
  FilterOptions with IgnoreSingles/IgnoreCompilations flags, read from
  artist_settings table via getArtistFilterOptions.
- Fix inconsistent error wrapping: GetExternalRelease now wraps errors
  with fmt.Errorf like all other functions in the package; updated test
  to use errors.Is for sql.ErrNoRows check.
- Add tests: FilterReleaseGroups ignore singles/compilations,
  SyncArtistDiscography per-artist type filtering, and FK-safe resync.

internal/musicbrainz/sync.go

@@ -2,6 +2,7 @@ package musicbrainz
 
 import (
 	"context"
+	"database/sql"
 	"fmt"
 	"time"
 
@@ -51,8 +52,12 @@ func SyncArtistDiscography(
 		return nil, fmt.Errorf("sync artist discography: fetch release groups for artist %s: %w", artistMBID, err)
 	}
 
-	// Step 4: Apply filtering.
-	filtered := FilterReleaseGroups(groups)
+	// Step 4: Apply filtering with per-artist type preferences.
+	opts, err := getArtistFilterOptions(db, artistMBID)
+	if err != nil {
+		return nil, fmt.Errorf("sync artist discography: read artist filter options: %w", err)
+	}
+	filtered := FilterReleaseGroups(groups, opts)
 
 	// Step 5: Upsert within a transaction — delete old entries first, then insert new ones.
 	now := time.Now().UTC()
@@ -80,6 +85,14 @@ func SyncArtistDiscography(
 	rows.Close()
 
 	// Delete old entries for this artist to avoid stale records.
+	// Must delete notifications_sent first to avoid FK violation since
+	// notifications_sent.rgid references external_releases.rgid.
+	if _, err := tx.Exec(
+		"DELETE FROM notifications_sent WHERE rgid IN (SELECT rgid FROM external_releases WHERE artist_id = ?)",
+		artistMBID,
+	); err != nil {
+		return nil, fmt.Errorf("sync artist discography: delete old notifications: %w", err)
+	}
 	if _, err := tx.Exec("DELETE FROM external_releases WHERE artist_id = ?", artistMBID); err != nil {
 		return nil, fmt.Errorf("sync artist discography: delete old releases: %w", err)
 	}
@@ -115,3 +128,20 @@ func SyncArtistDiscography(
 
 	return releases, nil
 }
+
+// getArtistFilterOptions reads per-artist type filtering preferences.
+// Defaults to no filtering if artist_settings row doesn't exist.
+func getArtistFilterOptions(db *database.DB, artistMBID string) (FilterOptions, error) {
+	var opts FilterOptions
+	err := db.Conn().QueryRow(
+		"SELECT COALESCE(ignore_singles, 0), COALESCE(ignore_compilations, 0) FROM artist_settings WHERE id = ?",
+		artistMBID,
+	).Scan(&opts.IgnoreSingles, &opts.IgnoreCompilations)
+	if err == sql.ErrNoRows {
+		return opts, nil
+	}
+	if err != nil {
+		return opts, fmt.Errorf("query artist filter options: %w", err)
+	}
+	return opts, nil
+}