Wait for the event loop to exit in integration tests

The test harness enqueued ErrQuit after a test finished, waited for the
program to go idle, then slept a fixed second and declared "gocui should
have already exited" if it hadn't. That fixed grace is fragile: under the
race detector the shutdown legitimately takes longer than a second, so
nearly every test failed with that message even though nothing was wrong.

Wait for the main loop to actually return instead. gocui now closes a
loopExited channel when MainLoop exits, and the harness blocks on it; the
existing 40s watchdog still fails a test whose loop genuinely never quits.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

pkg/gocui/gui.go

@@ -148,6 +148,10 @@ type Gui struct {
 	maxX, maxY               int
 	outputMode               OutputMode
 	stop                     chan struct{}
+	// loopExited is closed when MainLoop returns, so callers (e.g. the
+	// integration-test harness) can wait for the event loop to actually finish
+	// rather than polling or sleeping a fixed interval.
+	loopExited chan struct{}
 
 	// BgColor and FgColor allow to configure the background and foreground
 	// colors of the GUI.
@@ -260,6 +264,7 @@ func NewGui(opts NewGuiOpts) (*Gui, error) {
 	g.outputMode = opts.OutputMode
 
 	g.stop = make(chan struct{})
+	g.loopExited = make(chan struct{})
 
 	g.gEvents = make(chan GocuiEvent, 20)
 	g.userEvents = newUserEventQueue()
@@ -348,6 +353,11 @@ func (g *Gui) Close() {
 	Screen.Fini()
 }
 
+// LoopExited returns a channel that is closed once MainLoop has returned.
+func (g *Gui) LoopExited() <-chan struct{} {
+	return g.loopExited
+}
+
 // Size returns the terminal's size.
 func (g *Gui) Size() (x, y int) {
 	return g.maxX, g.maxY
@@ -965,6 +975,8 @@ func (g *Gui) SetManagerFunc(manager func(*Gui) error) {
 // MainLoop runs the main loop until an error is returned. A successful
 // finish should return ErrQuit.
 func (g *Gui) MainLoop() error {
+	defer close(g.loopExited)
+
 	g.uiThreadID.Store(goid.Get())
 
 	go func() {

pkg/gui/test_mode.go

@@ -40,11 +40,8 @@ func (gui *Gui) handleTestMode() {
 				return gocui.ErrQuit
 			})
 
-			waitUntilIdle()
-
-			time.Sleep(time.Second * 1)
-
-			log.Fatal("gocui should have already exited")
+			// Wait for the event loop to actually exit.
+			<-gui.g.LoopExited()
 		}()
 
 		if os.Getenv(components.WAIT_FOR_DEBUGGER_ENV_VAR) == "" {