protondrive: stop a call rejected during disconnect retrying without credentials

A call in flight when the remote was disconnected, and then rejected
as unauthorised, was sent again with empty credentials. It now fails
with the "not signed in" error instead.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/protondrive/session.go

@@ -224,6 +224,10 @@ func (s *session) call(ctx context.Context, opts *rest.Opts, request, response a
 		}
 	}
 	creds = s.current()
+	if creds.UID == "" {
+		// Signed out while the call was made.
+		return resp, s.signInNeeded(errNotSignedIn)
+	}
 	return s.do(ctx, opts, request, response, &creds)
 }
 

backend/protondrive/session_internal_test.go

@@ -526,3 +526,21 @@ func TestLogout(t *testing.T) {
 	old.adoptWait = 0
 	assert.ErrorIs(t, authCall(context.Background(), old), errSessionExpired)
 }
+
+func TestCallDuringLogout(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	srv := protontest.New(t)
+	s, _, _ := newTestSession(t, srv)
+	// The call is rejected only after the session has signed out.
+	srv.Inject(protontest.Fault{Method: "GET", Pattern: "/tests/auth", Times: 1, Status: http.StatusUnauthorized, Delay: 500 * time.Millisecond})
+	errc := make(chan error, 1)
+	go func() { errc <- authCall(ctx, s) }()
+	require.Eventually(t, func() bool { return srv.Requests()["GET /tests/auth"] == 1 }, 5*time.Second, 5*time.Millisecond)
+	require.NoError(t, s.logout(ctx))
+
+	err := <-errc
+	assert.ErrorIs(t, err, errNotSignedIn)
+	assert.Equal(t, 1, srv.Requests()["GET /tests/auth"], "retried without credentials")
+	assert.Zero(t, srv.Requests()[refreshRoute])
+}