Make the VNC server single-use and recognise crash-leftover desktop processes by their recorded command

client/vnc/server/server_test.go

@@ -681,44 +681,23 @@ func TestCloseAdmission_RefusesAndDrains(t *testing.T) {
 	}
 }
 
-// TestCloseAdmission_HandlerOutlivingDrain reproduces the restart hazard: Stop
-// gives up after handlerDrainTimeout, so a handler can still be running when a
-// later Start reopens admission. The counter must survive that (a sync.WaitGroup
-// panics on an Add racing the Wait it left behind), and the next Stop must wait
-// for both the straggler and the handlers admitted after the restart.
-func TestCloseAdmission_HandlerOutlivingDrain(t *testing.T) {
-	srv := &Server{log: log.WithField("test", t.Name())}
+// A Server is single-use. Stop closes the listener, capturer and injector it was
+// handed and cannot recreate, so a second Start would accept on a closed socket
+// and capture from a closed display. It must be refused instead.
+func TestStart_AfterStopIsRejected(t *testing.T) {
+	srv := New(Config{
+		Capturer:    &StubCapturer{},
+		Injector:    &StubInputInjector{},
+		DisableAuth: true,
+	})
+	addr := netip.MustParseAddrPort("127.0.0.1:0")
+	network := netip.MustParsePrefix("127.0.0.0/8")
 
-	require.True(t, srv.beginHandler())
-	firstDrain := srv.closeAdmission()
-	select {
-	case <-firstDrain:
-		t.Fatal("drained while a handler was still in flight")
-	default:
-	}
+	require.NoError(t, srv.Start(t.Context(), addr, network))
+	require.NoError(t, srv.Stop())
 
-	// What Start does after a drain that timed out.
-	srv.handlersMu.Lock()
-	srv.stopping = false
-	srv.handlersDrained = nil
-	srv.handlersMu.Unlock()
-
-	require.True(t, srv.beginHandler(), "a restarted server must admit handlers again")
-
-	secondDrain := srv.closeAdmission()
-	srv.endHandler() // the straggler from before the restart
-	select {
-	case <-secondDrain:
-		t.Fatal("drained before the post-restart handler finished")
-	default:
-	}
-
-	srv.endHandler()
-	select {
-	case <-secondDrain:
-	case <-time.After(time.Second):
-		t.Fatal("drain signal never fired after restart")
-	}
+	err := srv.Start(t.Context(), addr, network)
+	require.ErrorIs(t, err, errServerStopped, "a stopped server must not start again")
 }
 
 func TestAcceptRetryable(t *testing.T) {