fix: address code review findings

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)
 }