fix(restore): avoid duplicate completion locks for empty upload IDs

Keep the storage layer error precedence for missing buckets and uploads while retaining every real upload lock. Cover the alias with short deadlines and race-check the original complete-multipart suite in CI.

Signed-off-by: Feng Ruohang <rh@vonng.com>

cmd/restore-native_test.go

@@ -707,3 +707,35 @@ func (r *nativeRestorePartGateReader) Read(p []byte) (int, error) {
 	}
 	return r.ReadCloser.Read(p)
 }
+
+// Invalid upload paths must retain the backend's normal error precedence,
+// rather than reacquiring the object lock as the upload lock.
+func TestMultipartCompletionLockAlias(t *testing.T) {
+	for _, pools := range []int{1, 2} {
+		for _, id := range []string{"", ".", "./"} {
+			t.Run(fmt.Sprintf("pools=%d/id=%q", pools, id), func(t *testing.T) {
+				r := newRestoreSafetyTest(t, pools, versioning.Enabled)
+				for _, missingBucket := range []bool{false, true} {
+					bucket := r.bucket
+					if missingBucket {
+						bucket = "missing-bucket"
+					}
+					ctx, cancel := context.WithTimeout(t.Context(), 200*time.Millisecond)
+					_, err := r.z.CompleteMultipartUpload(ctx, bucket, r.object, id, nil, ObjectOptions{})
+					cancel()
+					if id != "" {
+						if !errors.As(err, &MalformedUploadID{}) {
+							t.Errorf("malformed upload: %v", err)
+						}
+					} else if missingBucket {
+						if !isErrBucketNotFound(err) {
+							t.Errorf("missing bucket: %v", err)
+						}
+					} else if !errors.As(err, &InvalidUploadID{}) {
+						t.Errorf("invalid upload: %v", err)
+					}
+				}
+			})
+		}
+	}
+}