Deferred redraw entering alternate screen:

- Immediately sends the new PTY size.
  - Suppresses incremental and full-window redraws during the transition.
  - Releases redraw after the next PTY read.
  - Uses a 50 ms fallback timer to avoid leaving the pane frozen

screen-write.c

@@ -146,7 +146,7 @@ screen_write_set_client_cb(struct tty_ctx *ttyctx, struct client *c)
 	if (wp->layout_cell == NULL)
 		return (0);
 
-	if (wp->flags & (PANE_REDRAW|PANE_DROP))
+	if (wp->flags & (PANE_REDRAW|PANE_DROP|PANE_REDRAWDEFER))
 		return (-1);
 	if (c->flags & CLIENT_REDRAWWINDOW) {
 		/*
@@ -3017,6 +3017,7 @@ screen_write_alternateon(struct screen_write_ctx *ctx, struct grid_cell *gc,
 		if (!TAILQ_EMPTY(&wp->resize_queue)) {
 			window_pane_send_resize(wp, wp->sx, wp->sy);
 			window_pane_clear_resizes(wp, NULL);
+			window_pane_defer_redraw(wp);
 		}
 		server_redraw_window_borders(wp->window);
 	}

server-client.c

@@ -2245,6 +2245,18 @@ server_client_any_pane_redraw(struct client *c)
 	return (0);
 }
 
+static int
+server_client_redraw_deferred(struct window *w)
+{
+	struct window_pane	*wp;
+
+	TAILQ_FOREACH(wp, &w->panes, entry) {
+		if (wp->flags & PANE_REDRAWDEFER)
+			return (1);
+	}
+	return (0);
+}
+
 /* Check for client redraws. */
 static void
 server_client_check_redraw(struct client *c)
@@ -2260,6 +2272,8 @@ server_client_check_redraw(struct client *c)
 
 	if (c->flags & (CLIENT_CONTROL|CLIENT_SUSPENDED))
 		return;
+	if (server_client_redraw_deferred(w))
+		return;
 	if (c->flags & CLIENT_ALLREDRAWFLAGS) {
 		log_debug("%s: redraw%s%s%s%s", c->name,
 		    (c->flags & CLIENT_REDRAWWINDOW) ? " window" : "",

tmux.h

@@ -1293,6 +1293,7 @@ struct window_pane {
 #define PANE_THEMECHANGED 0x2000
 #define PANE_UNSEENCHANGES 0x4000
 #define PANE_REDRAWSCROLLBAR 0x8000
+#define PANE_REDRAWDEFER 0x10000
 
 	u_int		 sb_slider_y;
 	u_int		 sb_slider_h;
@@ -1320,6 +1321,7 @@ struct window_pane {
 
 	struct window_pane_resizes resize_queue;
 	struct event	 resize_timer;
+	struct event	 redraw_timer;
 	struct event	 sync_timer;
 
 	struct input_ctx *ictx;
@@ -3584,6 +3586,8 @@ int		 window_pane_destroy_ready(struct window_pane *);
 void		 window_pane_resize(struct window_pane *, u_int, u_int);
 void		 window_pane_clear_resizes(struct window_pane *,
 		     struct window_pane_resize *);
+void		 window_pane_defer_redraw(struct window_pane *);
+void		 window_pane_finish_redraw(struct window_pane *);
 int		 window_pane_set_mode(struct window_pane *,
 		     struct window_pane *, const struct window_mode *,
 		     struct cmd_find_state *, struct args *);

window.c

@@ -72,6 +72,7 @@ static struct window_pane *window_pane_create(struct window *, u_int, u_int,
 		    u_int);
 static void	window_pane_destroy(struct window_pane *);
 static void	window_pane_scrollbar_timer(int, short, void *);
+static void	window_pane_redraw_timer(int, short, void *);
 static void	window_pane_full_size_offset(struct window_pane *wp,
 		    int *xoff, int *yoff, u_int *sx, u_int *sy);
 
@@ -1234,6 +1235,8 @@ window_pane_destroy(struct window_pane *wp)
 
 	if (event_initialized(&wp->resize_timer))
 		event_del(&wp->resize_timer);
+	if (event_initialized(&wp->redraw_timer))
+		event_del(&wp->redraw_timer);
 	if (event_initialized(&wp->sync_timer))
 		event_del(&wp->sync_timer);
 	if (event_initialized(&wp->sb_auto_timer))
@@ -1261,6 +1264,9 @@ window_pane_read_callback(__unused struct bufferevent *bufev, void *data)
 	char				*new_data;
 	size_t				 new_size;
 	struct client			*c;
+	int				 deferred;
+
+	deferred = (wp->flags & PANE_REDRAWDEFER);
 
 	if (wp->pipe_fd != -1) {
 		new_data = window_pane_get_new_data(wp, wpo, &new_size);
@@ -1276,6 +1282,8 @@ window_pane_read_callback(__unused struct bufferevent *bufev, void *data)
 			control_write_output(c, wp);
 	}
 	input_parse_pane(wp);
+	if (deferred)
+		window_pane_finish_redraw(wp);
 	bufferevent_disable(wp->event, EV_READ);
 }
 
@@ -1320,6 +1328,35 @@ window_pane_clear_resizes(struct window_pane *wp,
 	}
 }
 
+static void
+window_pane_redraw_timer(__unused int fd, __unused short events, void *arg)
+{
+	window_pane_finish_redraw(arg);
+}
+
+void
+window_pane_defer_redraw(struct window_pane *wp)
+{
+	struct timeval	 tv = { .tv_usec = 50000 };
+
+	wp->flags |= PANE_REDRAWDEFER;
+	if (!event_initialized(&wp->redraw_timer))
+		evtimer_set(&wp->redraw_timer, window_pane_redraw_timer, wp);
+	evtimer_del(&wp->redraw_timer);
+	evtimer_add(&wp->redraw_timer, &tv);
+}
+
+void
+window_pane_finish_redraw(struct window_pane *wp)
+{
+	if (~wp->flags & PANE_REDRAWDEFER)
+		return;
+	evtimer_del(&wp->redraw_timer);
+	wp->flags &= ~PANE_REDRAWDEFER;
+	wp->flags |= PANE_REDRAW;
+	server_redraw_window(wp->window);
+}
+
 void
 window_pane_resize(struct window_pane *wp, u_int sx, u_int sy)
 {