fix: address code review findings

internal/database/external_releases.go

@@ -29,7 +29,7 @@ func GetExternalRelease(db *DB, rgid string) (*ExternalRelease, error) {
 func SaveExternalRelease(db *DB, release *ExternalRelease) error {
 	var cachedAt interface{}
 	if !release.CachedAt.IsZero() {
-		cachedAt = release.CachedAt.UTC().Format("2006-01-02 15:04:05")
+		cachedAt = release.CachedAt
 	}
 	_, err := db.Conn().Exec(
 		"INSERT OR REPLACE INTO external_releases (rgid, artist_id, title, type, release_date, is_ignored, cached_at) VALUES (?, ?, ?, ?, ?, ?, ?)",
@@ -125,7 +125,7 @@ func GetExternalReleasesByArtistWithCache(db *DB, artistID string, ttl time.Dura
 	cutoff := time.Now().UTC().Add(-ttl)
 	rows, err := db.Conn().Query(
 		"SELECT rgid, artist_id, title, type, release_date, is_ignored, cached_at FROM external_releases WHERE artist_id = ? AND cached_at >= ?",
-		artistID, cutoff.Format("2006-01-02 15:04:05"),
+		artistID, cutoff,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("query cached external releases: %w", err)

internal/musicbrainz/sync.go

@@ -135,10 +135,9 @@ func SyncArtistDiscography(
 			ext.IsIgnored = ignored
 		}
 
-		cachedAtStr := ext.CachedAt.Format("2006-01-02 15:04:05")
 		if _, err := tx.Exec(
 			"INSERT INTO external_releases (rgid, artist_id, title, type, release_date, is_ignored, cached_at) VALUES (?, ?, ?, ?, ?, ?, ?)",
-			ext.RGID, ext.ArtistID, ext.Title, ext.Type, ext.ReleaseDate, ext.IsIgnored, cachedAtStr,
+			ext.RGID, ext.ArtistID, ext.Title, ext.Type, ext.ReleaseDate, ext.IsIgnored, ext.CachedAt,
 		); err != nil {
 			return nil, fmt.Errorf("sync artist discography: insert release %s: %w", rg.ID, err)
 		}

internal/scanner/scan.go

@@ -47,6 +47,7 @@ func ScanAll(ctx context.Context, db *database.DB, threshold float64) ([]Missing
 	}
 
 	var all []MissingRelease
+	var failedArtists []string
 	for _, s := range settings {
 		if err := ctx.Err(); err != nil {
 			return all, err
@@ -59,10 +60,15 @@ func ScanAll(ctx context.Context, db *database.DB, threshold float64) ([]Missing
 		missing, err := ScanArtist(ctx, db, s.ID, threshold)
 		if err != nil {
 			log.Printf("scan artist %s failed: %v", s.ID, err)
+			failedArtists = append(failedArtists, s.ID)
 			continue
 		}
 		all = append(all, missing...)
 	}
 
+	if n := len(failedArtists); n > 0 {
+		log.Printf("scan completed with %d artist(s) skipped due to errors: %v", n, failedArtists)
+	}
+
 	return all, nil
 }

internal/scanner/scanner.go

@@ -59,7 +59,10 @@ func Similarity(a, b string) float64 {
 }
 
 // IsMatch reports whether a and b are similar enough to be considered the
-// same release, given the provided threshold in [0.0, 1.0].
+// same release, given the provided threshold in [0.0, 1.0]. A threshold of 0
+// (unset) falls back to DefaultThreshold, so this primitive honors the same
+// zero-means-default contract as FindMissingReleases/ScanArtist/ScanAll rather
+// than treating 0 as "always match".
 func IsMatch(a, b string, threshold float64) bool {
-	return Similarity(a, b) >= threshold
+	return Similarity(a, b) >= resolveThreshold(threshold)
 }