fix: a closed terminal hangs its shell up instead of killing it, so the history is saved; idle shells end with their session, and on agent stop

internal/agent/session.go

@@ -54,6 +54,10 @@ func (a *Agent) bridgeStream(parent context.Context, sid string, rw io.ReadWrite
 	ctx, cancel := context.WithCancel(parent)
 	defer cancel()
 	defer rw.Close()
+	// A session closed from the panel (a tab reloaded, a window shut) ends
+	// the stream at once, not on its next output: an idle shell would live
+	// on until the agent stopped.
+	go func() { <-ctx.Done(); rw.Close() }()
 
 	// Downstream: pull input frames and write them to the stream.
 	go func() {