fix: add safety-net exit for bubbletea renderer deadlock on /exit

When the user types /exit, bubbletea's cursedRenderer can deadlock: its
ticker-driven flush goroutine holds a mutex while blocked writing to
stdout, and the event loop's final render() call after tea.Quit blocks
on the same mutex. p.Run() never returns and the process hangs.

Add a safety-net goroutine in cleanupAll() that calls os.Exit(0) after
5 seconds, guaranteeing the process terminates even when bubbletea's
renderer is deadlocked.

Fixes #2268

Assisted-By: docker-agent

Author: aheritier

pkg/tui/tui.go

@@ -2103,6 +2103,17 @@ func (m *appModel) cleanupAll() {
 	for _, ed := range m.editors {
 		ed.Cleanup()
 	}
+
+	// Safety net: force-exit if bubbletea's shutdown gets stuck.
+	// This can happen when the renderer's flush goroutine blocks on a
+	// stdout write (terminal buffer full) while holding the renderer
+	// mutex, preventing the event loop from completing the render call
+	// that follows tea.Quit.
+	go func() {
+		time.Sleep(shutdownTimeout)
+		slog.Warn("Graceful shutdown timed out, forcing exit")
+		exitFunc(0)
+	}()
 }
 
 // persistedSessionID returns the session-store ID that should be used for