Add clean command

internal/artifacts/paths.go

@@ -91,9 +91,14 @@ func SessionSpoolAudioDir(spoolRoot, campaign, sessionID, runID string) string {
 	return filepath.Join(spoolRoot, campaign, sessionID, runID, config.PathAudioDirSegment)
 }
 
+// SessionSpoolDir returns the campaign/session scoped local spool root.
+func SessionSpoolDir(spoolRoot, campaign, sessionID string) string {
+	return filepath.Join(spoolRoot, campaign, sessionID)
+}
+
 // SessionSpoolRestoreAudioDir returns the local spool audio path for restore downloads.
 func SessionSpoolRestoreAudioDir(spoolRoot, campaign, sessionID string) string {
-	return filepath.Join(spoolRoot, campaign, sessionID, "restore", config.PathAudioDirSegment)
+	return filepath.Join(SessionSpoolDir(spoolRoot, campaign, sessionID), "restore", config.PathAudioDirSegment)
 }
 
 // S3AudioCachePath returns the durable local cache path for one S3 audio object.
@@ -120,6 +125,17 @@ func S3AudioCachePath(cacheRoot, bucket, key string) (string, error) {
 	return filepath.Join(root, "s3", bucket, filepath.FromSlash(cleanKey)), nil
 }
 
+// S3AudioCacheNamespaceDir returns the durable local cache namespace for all
+// Narratio S3 audio objects under one bucket/root prefix.
+func S3AudioCacheNamespaceDir(cacheRoot, bucket, rootPrefix string) (string, error) {
+	sentinelKey := path.Join(cleanS3PathPart(rootPrefix), config.S3CampaignsSegment, ".narratio-cache-sentinel")
+	sentinelPath, err := S3AudioCachePath(cacheRoot, bucket, sentinelKey)
+	if err != nil {
+		return "", err
+	}
+	return filepath.Dir(sentinelPath), nil
+}
+
 func cleanCacheS3Key(key string) string {
 	normalized := strings.ReplaceAll(strings.TrimSpace(key), `\`, "/")
 	normalized = strings.Trim(normalized, "/")