Fix lint and failing tests

proxy/internal/flock/flock_other.go

@@ -11,7 +11,7 @@ import (
 // that no lock was acquired; callers must treat a nil file as "proceed
 // without lock" rather than "lock held by someone else."
 func Lock(_ context.Context, _ string) (*os.File, error) {
-	return nil, nil
+	return nil, nil //nolint:nilnil // intentional: nil file signals locking unsupported on this platform
 }
 
 // Unlock is a no-op on non-Unix platforms.

proxy/internal/metrics/metrics_test.go

@@ -53,6 +53,9 @@ func TestMetrics_RoundTripper(t *testing.T) {
 		t.Run(name, func(t *testing.T) {
 			rt := m.RoundTripper(test.roundTripper)
 			res, err := rt.RoundTrip(test.request)
+			if res != nil && res.Body != nil {
+				defer res.Body.Close()
+			}
 			if diff := cmp.Diff(test.err, err); diff != "" {
 				t.Errorf("Incorrect error (-want +got):\n%s", diff)
 			}