Merge remote-tracking branch 'refs/remotes/tmux-openbsd/master'

* refs/remotes/tmux-openbsd/master:
  Sync redraw should use the given rows not the scroll region now.
  Instead of redrawing the entire pane or scene when moving or redrawing a pane, add damage rectangles and redraw only the affected spans. From Michael Grant.
  Do not leak client if lost before configuration is loaded, and do not load multiple times. GitHub issues 5661 and 5662 from Alexandre Fiori.
  Restore the zoom when swap-pane refuses a floating pane, GitHub issue 5660 from Alexandre Fiori.
  Do not use client for copy-mode -S if NULL, reported by Martin Vlach.

cfg.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: cfg.c,v 1.91 2026/08/03 13:38:42 nicm Exp $ */
+/* $OpenBSD: cfg.c,v 1.92 2026/10/02 12:28:07 nicm Exp $ */
 
 /*
  * Copyright (c) 2008 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -31,14 +31,17 @@ int			  cfg_finished;
 static char		**cfg_causes;
 static u_int		  cfg_ncauses;
 static struct cmdq_item	 *cfg_item;
+static int		  cfg_started;
 
 int                       cfg_quiet = 1;
 char                    **cfg_files;
 u_int                     cfg_nfiles;
 
 static enum cmd_retval
-cfg_client_done(__unused struct cmdq_item *item, __unused void *data)
+cfg_client_done(struct cmdq_item *item, __unused void *data)
 {
+	if (cmdq_get_client(item)->flags & CLIENT_DEAD)
+		return (CMD_RETURN_NORMAL);
 	if (!cfg_finished)
 		return (CMD_RETURN_WAIT);
 	return (CMD_RETURN_NORMAL);
@@ -53,14 +56,28 @@ cfg_done(__unused struct cmdq_item *item, __unused void *data)
 
 	cfg_show_causes(NULL);
 
-	if (cfg_item != NULL)
+	if (cfg_item != NULL) {
 		cmdq_continue(cfg_item);
+		cfg_item = NULL;
+	}
 
 	prompt_load_history();
 
 	return (CMD_RETURN_NORMAL);
 }
 
+void
+cfg_client_lost(struct client *c)
+{
+	if (c != cfg_client)
+		return;
+	cfg_client = NULL;
+	if (cfg_item != NULL) {
+		cmdq_continue(cfg_item);
+		cfg_item = NULL;
+	}
+}
+
 void
 start_cfg(void)
 {
@@ -77,12 +94,19 @@ start_cfg(void)
 	 * Because start_cfg() is called so early, we can be sure the client's
 	 * command queue is currently empty and our callback will be at the
 	 * front - we need to get in before MSG_COMMAND.
+	 *
+	 * If the initial client is lost before the configuration finishes, the
+	 * next client to identify is first in the list and ends up here. Block
+	 * it instead, but do not load the files again.
 	 */
 	cfg_client = c = TAILQ_FIRST(&clients);
 	if (c != NULL) {
 		cfg_item = cmdq_get_callback(cfg_client_done, NULL);
 		cmdq_append(c, cfg_item);
 	}
+	if (cfg_started)
+		return;
+	cfg_started = 1;
 
 	if (cfg_quiet)
 		flags = CMD_PARSE_QUIET;

cmd-attach-session.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: cmd-attach-session.c,v 1.91 2026/07/10 13:38:45 nicm Exp $ */
+/* $OpenBSD: cmd-attach-session.c,v 1.92 2026/10/02 12:48:52 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -91,8 +91,10 @@ cmd_attach_session(struct cmdq_item *item, const char *tflag, int dflag,
 	wp = target.wp;
 
 	if (wl != NULL) {
-		if (wp != NULL)
+		if (wp != NULL) {
+			window_redraw_active_switch(wp->window, wp);
 			window_set_active_pane(wp->window, wp, 1);
+		}
 		session_set_current(s, wl);
 		if (wp != NULL)
 			cmd_find_from_winlink_pane(current, wl, wp, 0);

cmd-copy-mode.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: cmd-copy-mode.c,v 1.54 2026/07/14 17:17:17 nicm Exp $ */
+/* $OpenBSD: cmd-copy-mode.c,v 1.55 2026/10/02 12:12:51 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -103,6 +103,8 @@ cmd_copy_mode_exec(struct cmd *self, struct cmdq_item *item)
 	if (args_has(args, 'd'))
 		window_copy_pagedown(wp, 0, args_has(args, 'e'));
 	if (args_has(args, 'S')) {
+		if (c == NULL)
+			return (CMD_RETURN_NORMAL);
 		tty_window_offset(&c->tty, &tty_ox, &tty_oy, &tty_sx, &tty_sy);
 		window_copy_scroll(wp, c->tty.mouse_slider_mpos, event->m.y,
 		    tty_oy, args_has(args, 'e'));

cmd-join-pane.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: cmd-join-pane.c,v 1.75 2026/09/21 10:33:16 nicm Exp $ */
+/* $OpenBSD: cmd-join-pane.c,v 1.76 2026/10/02 12:48:52 nicm Exp $ */
 
 /*
  * Copyright (c) 2011 George Nachman <tmux@georgester.com>
@@ -307,7 +307,7 @@ cmd_join_pane_mouse_move(struct client *c, struct mouse_event *m)
 	struct window		*w;
 	struct window_pane	*wp;
 	struct layout_cell	*lc;
-	int			 y, ly, x, lx;
+	int			 y, ly, x, lx, oxoff, oyoff, osx, osy;
 
 	wp = cmd_mouse_pane(m, NULL, &wl);
 	if (wp == NULL) {
@@ -329,10 +329,16 @@ cmd_join_pane_mouse_move(struct client *c, struct mouse_event *m)
 		ly = m->statusat - 1;
 
 	if (x != lx || y != ly) {
+		oxoff = wp->xoff;
+		oyoff = wp->yoff;
+		osx = wp->sx;
+		osy = wp->sy;
+
 		lc->g.xoff += x - lx;
 		lc->g.yoff += y - ly;
 		layout_fix_panes(w, NULL);
-		server_redraw_window(w);
+
+		window_redraw_floating_pane(wp, oxoff, oyoff, osx, osy);
 		server_redraw_window_borders(w);
 	}
 }

cmd-resize-pane.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: cmd-resize-pane.c,v 1.69 2026/09/21 10:33:16 nicm Exp $ */
+/* $OpenBSD: cmd-resize-pane.c,v 1.70 2026/10/02 12:48:52 nicm Exp $ */
 
 /*
  * Copyright (c) 2009 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -237,8 +237,8 @@ cmd_resize_pane_mouse_resize_move_floating(struct client *c,
 	struct window_pane	*wp;
 	struct layout_cell	*lc;
 	int			 y, ly, x, lx, sx, sy, new_sx, new_sy;
-	int			 left, right;
-	int			 new_xoff, new_yoff, resizes = 0;
+	int			 left, right, resizes = 0;
+	int			 new_xoff, new_yoff, old_xoff, old_yoff;
 
 	wp = cmd_mouse_pane(m, NULL, &wl);
 	if (wp == NULL) {
@@ -249,6 +249,8 @@ cmd_resize_pane_mouse_resize_move_floating(struct client *c,
 	lc = wp->layout_cell;
 	sx = wp->sx;
 	sy = wp->sy;
+	old_xoff = wp->xoff;
+	old_yoff = wp->yoff;
 	left = wp->xoff - 1;
 	right = wp->xoff + sx;
 	if (window_pane_scrollbar_reserve(wp) &&
@@ -348,7 +350,7 @@ cmd_resize_pane_mouse_resize_move_floating(struct client *c,
 	}
 	if (resizes != 0) {
 		layout_fix_panes(w, NULL);
-		server_redraw_window(w);
+		window_redraw_floating_pane(wp, old_xoff, old_yoff, sx, sy);
 		server_redraw_window_borders(w);
 	}
 }

cmd-split-window.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: cmd-split-window.c,v 1.151 2026/09/10 11:02:18 nicm Exp $ */
+/* $OpenBSD: cmd-split-window.c,v 1.152 2026/10/02 12:48:52 nicm Exp $ */
 
 /*
  * Copyright (c) 2009 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -362,6 +362,7 @@ cmd_split_window_mouse_resize(struct client *c, struct mouse_event *m)
 	enum pane_lines		 lines;
 	u_int			 sx, sy;
 	int			 x, y, xoff, yoff, border;
+	int			 oxoff, oyoff, osx, osy;
 
 	if (c->tty.mouse_last_pane == -1)
 		return;
@@ -417,8 +418,14 @@ cmd_split_window_mouse_resize(struct client *c, struct mouse_event *m)
 	if (sy < PANE_MINIMUM)
 		sy = PANE_MINIMUM;
 
+	oxoff = wp->xoff;
+	oyoff = wp->yoff;
+	osx = wp->sx;
+	osy = wp->sy;
+
 	layout_set_size(lc, sx, sy, xoff, yoff);
 	layout_fix_panes(w, NULL);
-	server_redraw_window(w);
+
+	window_redraw_floating_pane(wp, oxoff, oyoff, osx, osy);
 	server_redraw_window_borders(w);
 }

cmd-swap-pane.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: cmd-swap-pane.c,v 1.55 2026/07/15 13:02:33 nicm Exp $ */
+/* $OpenBSD: cmd-swap-pane.c,v 1.56 2026/10/02 12:23:44 nicm Exp $ */
 
 /*
  * Copyright (c) 2009 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -88,7 +88,7 @@ cmd_swap_pane_exec(struct cmd *self, struct cmdq_item *item)
 	if (args_has(args, 'D')) {
 		if (window_pane_is_floating(dst_wp)) {
 			cmdq_error(item, "cannot swap down on floating pane");
-			return (CMD_RETURN_ERROR);
+			goto error;
 		}
 		src_w = dst_w;
 		src_wp = TAILQ_NEXT(dst_wp, entry);
@@ -100,7 +100,7 @@ cmd_swap_pane_exec(struct cmd *self, struct cmdq_item *item)
 	} else if (args_has(args, 'U')) {
 		if (window_pane_is_floating(dst_wp)) {
 			cmdq_error(item, "cannot swap up on floating pane");
-			return (CMD_RETURN_ERROR);
+			goto error;
 		}
 		src_w = dst_w;
 		src_wp = TAILQ_PREV(dst_wp, window_panes, entry);
@@ -202,4 +202,9 @@ out:
 	if (src_w != dst_w && window_pop_zoom(dst_w))
 		server_redraw_window(dst_w);
 	return (CMD_RETURN_NORMAL);
+
+error:
+	if (window_pop_zoom(dst_w))
+		server_redraw_window(dst_w);
+	return (CMD_RETURN_ERROR);
 }

layout.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: layout.c,v 1.101 2026/09/20 08:42:46 nicm Exp $ */
+/* $OpenBSD: layout.c,v 1.102 2026/10/02 12:48:52 nicm Exp $ */
 
 /*
  * Copyright (c) 2009 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -469,7 +469,6 @@ layout_fix_panes(struct window *w, struct window_pane *skip)
 					sx = PANE_MINIMUM;
 				else
 					sx = sx - sb_w - sb_pad;
-			wp->flags |= PANE_REDRAWSCROLLBAR;
 		}
 
 		window_pane_resize(wp, sx, sy);
@@ -477,8 +476,11 @@ layout_fix_panes(struct window *w, struct window_pane *skip)
 		if (wp->xoff != old_xoff ||
 		    wp->yoff != old_yoff ||
 		    wp->sx != old_sx ||
-		    wp->sy != old_sy)
+		    wp->sy != old_sy) {
+			if (window_pane_scrollbar_reserve(wp))
+				wp->flags |= PANE_REDRAWSCROLLBAR;
 			changed = 1;
+		}
 	}
 	if (changed)
 		redraw_invalidate_scene(w);

screen-redraw.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: screen-redraw.c,v 1.162 2026/09/24 11:19:39 nicm Exp $ */
+/* $OpenBSD: screen-redraw.c,v 1.163 2026/10/02 12:48:52 nicm Exp $ */
 
 /*
  * Copyright (c) 2026 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -204,14 +204,36 @@ struct redraw_scene {
 	u_int			 oy;
 };
 
+/* A damaged rectangle in a window. */
+struct redraw_damage {
+	u_int				 x;
+	u_int				 y;
+	u_int				 sx;
+	u_int				 sy;
+
+	TAILQ_ENTRY(redraw_damage)	entry;
+};
+
+/*
+ * If there are more damage rectangles than this, they are collapsed into
+ * one.
+ */
+#define REDRAW_DAMAGE_MAX 16
+
 /* Cell for building the scene. */
 struct redraw_build_cell {
 	struct redraw_span_data	 data;
 };
-
 static struct redraw_build_cell	*redraw_cells;
 static size_t			 redraw_ncells;
 
+/*
+ * We can reuse the same pane status lines during one damage redraw, but when
+ * we enter a new one, the client or format variables may have changed, so we
+ * need to make them again. The generation is increased so this happens.
+ */
+static u_int	redraw_status_generation;
+
 /* Context for building the scene. */
 struct redraw_build_ctx {
 	struct client				*c;
@@ -1054,6 +1076,13 @@ redraw_free_scene(struct redraw_scene *scene)
 	free(scene);
 }
 
+/* Does a client's cached scene show this window? */
+int
+redraw_client_has_window(struct client *c, struct window *w)
+{
+	return (c->redraw_scene != NULL && c->redraw_scene->w == w);
+}
+
 /* Mark a window's cached redraw scenes as out of date. */
 void
 redraw_invalidate_scene(struct window *w)
@@ -1061,6 +1090,104 @@ redraw_invalidate_scene(struct window *w)
 	w->redraw_scene_generation++;
 }
 
+/* Free all pending damage for a window. */
+void
+redraw_free_damage(struct window *w)
+{
+	struct redraw_damage	*rd, *rd1;
+
+	TAILQ_FOREACH_SAFE(rd, &w->damage, entry, rd1) {
+		TAILQ_REMOVE(&w->damage, rd, entry);
+		free(rd);
+	}
+	w->damage_count = 0;
+}
+
+/* Collapse all pending damage for a window into one rectangle. */
+static void
+redraw_collapse_damage(struct window *w)
+{
+	struct redraw_damage	*rd, *rd1, *first;
+	u_int			 x0, y0, x1, y1;
+
+	first = TAILQ_FIRST(&w->damage);
+	if (first == NULL)
+		return;
+	x0 = first->x;
+	y0 = first->y;
+	x1 = first->x + first->sx;
+	y1 = first->y + first->sy;
+
+	TAILQ_FOREACH_SAFE(rd, &w->damage, entry, rd1) {
+		if (rd->x < x0)
+			x0 = rd->x;
+		if (rd->y < y0)
+			y0 = rd->y;
+		if (rd->x + rd->sx > x1)
+			x1 = rd->x + rd->sx;
+		if (rd->y + rd->sy > y1)
+			y1 = rd->y + rd->sy;
+		if (rd != first) {
+			TAILQ_REMOVE(&w->damage, rd, entry);
+			free(rd);
+		}
+	}
+
+	first->x = x0;
+	first->y = y0;
+	first->sx = x1 - x0;
+	first->sy = y1 - y0;
+	w->damage_count = 1;
+}
+
+/* Record window damage, merging nearby rectangles and limiting the count. */
+void
+redraw_damage_window(struct window *w, u_int x, u_int y, u_int sx, u_int sy)
+{
+	struct redraw_damage	*rd;
+	u_int			 x0, y0, x1, y1, area, union_area;
+
+	if (x >= w->sx || y >= w->sy)
+		return;
+	if (x + sx > w->sx)
+		sx = w->sx - x;
+	if (y + sy > w->sy)
+		sy = w->sy - y;
+	if (sx == 0 || sy == 0)
+		return;
+
+	TAILQ_FOREACH(rd, &w->damage, entry) {
+		if (x > rd->x + rd->sx || rd->x > x + sx ||
+		    y > rd->y + rd->sy || rd->y > y + sy)
+			continue;
+
+		x0 = (x < rd->x) ? x : rd->x;
+		y0 = (y < rd->y) ? y : rd->y;
+		x1 = (x + sx > rd->x + rd->sx) ? x + sx : rd->x + rd->sx;
+		y1 = (y + sy > rd->y + rd->sy) ? y + sy : rd->y + rd->sy;
+
+		area = sx * sy + rd->sx * rd->sy;
+		union_area = (x1 - x0) * (y1 - y0);
+		if (union_area > 2 * area)
+			continue;
+
+		rd->x = x0;
+		rd->y = y0;
+		rd->sx = x1 - x0;
+		rd->sy = y1 - y0;
+		return;
+	}
+
+	rd = xcalloc(1, sizeof *rd);
+	rd->x = x;
+	rd->y = y;
+	rd->sx = sx;
+	rd->sy = sy;
+	TAILQ_INSERT_TAIL(&w->damage, rd, entry);
+	if (++w->damage_count > REDRAW_DAMAGE_MAX)
+		redraw_collapse_damage(w);
+}
+
 /* Mark all cached redraw scenes as out of date. */
 void
 redraw_invalidate_all_scenes(void)
@@ -1603,6 +1730,24 @@ redraw_set_draw_context(struct redraw_draw_ctx *dctx,
 		dctx->flags |= REDRAW_ISOLATES;
 }
 
+/* Build a pane prompt. */
+static void
+redraw_make_pane_prompt(struct window_pane *wp, struct screen *screen)
+{
+	struct screen_write_ctx	 ctx;
+	struct prompt_draw_data	 pdd;
+
+	screen_init(screen, wp->sx, 1, 0);
+	screen_write_start(&ctx, screen);
+	pdd.ctx = &ctx;
+	pdd.cursor_x = &wp->prompt_cx;
+	pdd.area_x = 0;
+	pdd.area_width = wp->sx;
+	pdd.prompt_line = 0;
+	prompt_draw(wp->prompt, &pdd);
+	screen_write_stop(&ctx);
+}
+
 /* Draw a pane's prompt over its content. */
 static void
 redraw_draw_pane_prompt(struct redraw_draw_ctx *dctx, struct window_pane *wp)
@@ -1611,8 +1756,6 @@ redraw_draw_pane_prompt(struct redraw_draw_ctx *dctx, struct window_pane *wp)
 	struct client		*c = scene->c;
 	struct tty		*tty = &c->tty;
 	struct screen		 screen;
-	struct screen_write_ctx	 ctx;
-	struct prompt_draw_data	 pdd;
 	int			 ox = scene->ox, oy = scene->oy;
 	int			 sx = scene->sx, sy = scene->sy;
 	int			 line, cy, px, offset, width, wy;
@@ -1645,16 +1788,7 @@ redraw_draw_pane_prompt(struct redraw_draw_ctx *dctx, struct window_pane *wp)
 	if (px + width > sx)
 		width = sx - px;
 
-	screen_init(&screen, wp->sx, 1, 0);
-	screen_write_start(&ctx, &screen);
-	pdd.ctx = &ctx;
-	pdd.cursor_x = &wp->prompt_cx;
-	pdd.area_x = 0;
-	pdd.area_width = wp->sx;
-	pdd.prompt_line = 0;
-	prompt_draw(wp->prompt, &pdd);
-	screen_write_stop(&ctx);
-
+	redraw_make_pane_prompt(wp, &screen);
 	tty_draw_line(tty, &screen, offset, 0, width, px, cy, NULL);
 	screen_free(&screen);
 }
@@ -1684,7 +1818,9 @@ redraw_draw(struct client *c, struct window_pane *wp, int flags)
 			redraw = status_prompt_redraw(c);
 		else
 			redraw = status_redraw(c);
-		if (!redraw && !REDRAW_IS_ALL(flags)) {
+		if (!redraw &&
+		    (~c->flags & CLIENT_REDRAWSTATUSALWAYS) &&
+		    !REDRAW_IS_ALL(flags)) {
 			flags &= ~REDRAW_STATUS;
 			if (flags == 0)
 				return;
@@ -1842,7 +1978,7 @@ redraw_screen(struct client *c)
 	else {
 		if (c->flags & CLIENT_REDRAWBORDERS)
 			flags |= (REDRAW_PANE_BORDER|REDRAW_PANE_STATUS);
-		if (c->flags & CLIENT_REDRAWSTATUS)
+		if (c->flags & (CLIENT_REDRAWSTATUS|CLIENT_REDRAWSTATUSALWAYS))
 			flags |= (REDRAW_STATUS|REDRAW_PANE_STATUS);
 		if (c->flags & CLIENT_REDRAWMENU)
 			flags |= REDRAW_MENU;
@@ -1868,3 +2004,138 @@ redraw_pane_scrollbar(struct client *c, struct window_pane *wp)
 {
 	redraw_draw(c, wp, REDRAW_PANE_SCROLLBAR);
 }
+
+/* Rebuild damaged pane status. */
+static void
+redraw_damage_refresh_status(struct redraw_draw_ctx *dctx,
+    struct window_pane *wp)
+{
+	struct redraw_span	*first;
+	u_int			 g = wp->status_generation, width;
+
+	if ((wp->flags & PANE_NEWSTATUS) && g == redraw_status_generation)
+		return;
+	width = redraw_pane_status_width(dctx, wp, &first);
+	if (width != 0) {
+		window_make_pane_status(wp, dctx->scene->c, width, first);
+		wp->flags |= PANE_NEWSTATUS;
+		wp->status_generation = redraw_status_generation;
+	}
+}
+
+/* Draw a pane's prompt over a damaged span. */
+static void
+redraw_damage_draw_pane_prompt(struct redraw_draw_ctx *dctx,
+    struct redraw_span *span, u_int y)
+{
+	struct redraw_scene	*scene = dctx->scene;
+	struct window_pane	*wp = span->data.p.wp;
+	struct tty		*tty = &scene->c->tty;
+	struct screen		 screen;
+	u_int			 px = span->data.p.px, width, prompt_y;
+
+	if (wp->prompt == NULL || wp->sx == 0 || wp->sy == 0)
+		return;
+	if (dctx->flags & REDRAW_STATUS_TOP)
+		prompt_y = 0;
+	else
+		prompt_y = wp->sy - 1;
+	if (span->data.p.py != prompt_y)
+		return;
+	redraw_make_pane_prompt(wp, &screen);
+	if (px < screen_size_x(&screen)) {
+		width = span->width;
+		if (width > screen_size_x(&screen) - px)
+			width = screen_size_x(&screen) - px;
+		tty_draw_line(tty, &screen, px, 0, width, span->x, y, NULL);
+	}
+	screen_free(&screen);
+}
+
+/* Draw the spans intersecting a damaged rectangle. */
+static void
+redraw_draw_damage_rectangle(struct redraw_draw_ctx *dctx, u_int x, u_int y,
+    u_int sx, u_int sy)
+{
+	struct redraw_scene	*scene = dctx->scene;
+	struct redraw_line	*line;
+	struct redraw_spans	*spans;
+	struct redraw_span	*span;
+	u_int			 cy, yy, type;
+
+	if (x >= scene->sx || y >= scene->sy)
+		return;
+	if (x + sx > scene->sx)
+		sx = scene->sx - x;
+	if (y + sy > scene->sy)
+		sy = scene->sy - y;
+	if (sx == 0 || sy == 0)
+		return;
+
+	for (yy = y; yy < y + sy; yy++) {
+		line = &scene->lines[yy];
+		if (dctx->flags & REDRAW_STATUS_TOP)
+			cy = dctx->status_lines + yy;
+		else
+			cy = yy;
+		for (type = 0; type < REDRAW_SPAN_TYPES; type++) {
+			spans = &line->spans[type];
+			TAILQ_FOREACH(span, spans, entry) {
+				if (span->x >= x + sx)
+					continue;
+				if (span->x + span->width <= x)
+					continue;
+				if (type == REDRAW_SPAN_STATUS) {
+					redraw_damage_refresh_status(dctx,
+					    span->data.st.wp);
+				}
+				redraw_draw_span(dctx, span, cy);
+				if (type == REDRAW_SPAN_PANE) {
+					redraw_damage_draw_pane_prompt(dctx,
+					    span, cy);
+				}
+			}
+		}
+	}
+}
+
+/* Draw pending window damage on this client. */
+void
+redraw_client_damage(struct client *c)
+{
+	struct window		*w = c->session->curw->window;
+	struct window_pane	*wp;
+	struct redraw_scene	*scene;
+	struct redraw_draw_ctx	 dctx;
+	struct redraw_damage	*rd;
+	u_int			 ox, oy, sx, sy, x0, y0, x1, y1;
+
+	if (TAILQ_EMPTY(&w->damage))
+		return;
+	redraw_status_generation++;
+
+	scene = redraw_get_scene(c);
+	if (scene == NULL)
+		return;
+	redraw_set_draw_context(&dctx, scene);
+	redraw_get_window_offset(c, &ox, &oy, &sx, &sy);
+
+	TAILQ_FOREACH(wp, &w->panes, entry) {
+		wp->border_gc_set = 0;
+		wp->active_border_gc_set = 0;
+	}
+
+	tty_sync_start(&c->tty);
+	tty_update_mode(&c->tty, c->tty.mode & ~CURSOR_MODES, NULL);
+
+	TAILQ_FOREACH(rd, &w->damage, entry) {
+		x0 = (rd->x > ox) ? rd->x : ox;
+		y0 = (rd->y > oy) ? rd->y : oy;
+		x1 = (rd->x + rd->sx < ox + sx) ? rd->x + rd->sx : ox + sx;
+		y1 = (rd->y + rd->sy < oy + sy) ? rd->y + rd->sy : oy + sy;
+		if (x0 < x1 && y0 < y1) {
+			redraw_draw_damage_rectangle(&dctx, x0 - ox, y0 - oy,
+			    x1 - x0, y1 - y0);
+		}
+	}
+}

screen-write.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: screen-write.c,v 1.294 2026/09/28 10:10:16 nicm Exp $ */
+/* $OpenBSD: screen-write.c,v 1.296 2026/10/02 12:53:26 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -122,14 +122,26 @@ screen_write_set_cursor(struct screen_write_ctx *ctx, int cx, int cy)
 		evtimer_add(&w->offset_timer, &tv);
 }
 
-/* Do a full redraw. */
+/* Redraw lines. */
 static void
-screen_write_redraw_cb(const struct tty_ctx *ttyctx)
+screen_write_redraw_cb(const struct tty_ctx *ttyctx, u_int py, u_int ny)
 {
 	struct window_pane	*wp = ttyctx->arg;
+	int			 x0, y0, x1, y1;
 
-	if (wp != NULL)
-		wp->flags |= PANE_REDRAW;
+	if (wp == NULL)
+		return;
+
+	x0 = wp->xoff;
+	y0 = wp->yoff + (int)py;
+	x1 = x0 + (int)wp->sx;
+	y1 = y0 + (int)ny;
+	if (x0 < 0)
+		x0 = 0;
+	if (y0 < 0)
+		y0 = 0;
+	if (x1 > x0 && y1 > y0)
+		redraw_damage_window(wp->window, x0, y0, x1 - x0, y1 - y0);
 }
 
 /* Update context for client. */
@@ -1376,11 +1388,11 @@ screen_write_sync_scroll_dirty(struct screen_write_ctx *ctx)
 
 /* Redraw the scrolled lines for a client which cannot scroll them. */
 static void
-screen_write_sync_redraw_cb(const struct tty_ctx *ttyctx)
+screen_write_sync_redraw_cb(const struct tty_ctx *ttyctx, u_int py, u_int ny)
 {
 	struct window_pane	*wp = ttyctx->arg;
 
-	bit_nset(wp->sync_dirty, wp->sync_rupper, wp->sync_rlower);
+	bit_nset(wp->sync_dirty, py, py + ny - 1);
 }
 
 /* Send the deferred scroll to the client. */
@@ -2272,7 +2284,7 @@ screen_write_fullredraw(struct screen_write_ctx *ctx)
 
 	screen_write_initctx(ctx, &ttyctx, 1, 0);
 	if (ttyctx.redraw_cb != NULL)
-		ttyctx.redraw_cb(&ttyctx);
+		ttyctx.redraw_cb(&ttyctx, 0, ttyctx.sy);
 }
 
 /* Trim collected items. */
@@ -3290,7 +3302,7 @@ screen_write_alternateon(struct screen_write_ctx *ctx, struct grid_cell *gc,
 
 	screen_write_initctx(ctx, &ttyctx, 1, 0);
 	if (ttyctx.redraw_cb != NULL)
-		ttyctx.redraw_cb(&ttyctx);
+		ttyctx.redraw_cb(&ttyctx, 0, ttyctx.sy);
 }
 
 /* Turn alternate screen off. */
@@ -3315,5 +3327,5 @@ screen_write_alternateoff(struct screen_write_ctx *ctx, struct grid_cell *gc,
 
 	screen_write_initctx(ctx, &ttyctx, 1, 0);
 	if (ttyctx.redraw_cb != NULL)
-		ttyctx.redraw_cb(&ttyctx);
+		ttyctx.redraw_cb(&ttyctx, 0, ttyctx.sy);
 }

server-client.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: server-client.c,v 1.515 2026/09/28 11:25:51 nicm Exp $ */
+/* $OpenBSD: server-client.c,v 1.517 2026/10/02 12:48:52 nicm Exp $ */
 
 /*
  * Copyright (c) 2009 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -356,7 +356,13 @@ server_client_set_session(struct client *c, struct session *s)
 		tty_update_client_offset(c);
 		status_timer_start(c);
 		server_client_fire_session_changed(c, old);
-		server_redraw_client(c);
+
+		/*
+		 * Redraw if the session or displayed window changed. Use the
+		 * cached scene because the session's current window is already set.
+		 */
+		if (old != s || !redraw_client_has_window(c, s->curw->window))
+			server_redraw_client(c);
 	}
 
 	server_check_unattached();
@@ -369,8 +375,7 @@ server_client_lost(struct client *c)
 {
 	struct client_file	*cf, *cf1;
 
-	if (cfg_client == c)
-		cfg_client = NULL;
+	cfg_client_lost(c);
 	c->flags |= CLIENT_DEAD;
 
 	status_prompt_clear(c);
@@ -1349,10 +1354,11 @@ server_client_key_callback(struct cmdq_item *item, void *data)
 		m->key = key;
 
 		/*
-		 * Mouse drag is in progress, so fire the callback (now that
-		 * the mouse event is valid).
+		 * Synchronize direct drag output with the later damage redraw
+		 * before invoking the drag callback.
 		 */
 		if ((key & KEYC_MASK_KEY) == KEYC_DRAGGING) {
+			tty_sync_start(&c->tty);
 			c->tty.mouse_drag_update(c, m);
 			goto out;
 		}
@@ -1779,8 +1785,8 @@ server_client_loop(void)
 	}
 
 	/*
-	 * Any windows will have been redrawn as part of clients, so clear
-	 * their flags now.
+	 * Clear window redraw state after processing all clients. Deferred
+	 * redraws are preserved in client flags.
 	 */
 	RB_FOREACH(w, windows, &windows) {
 		TAILQ_FOREACH(wp, &w->panes, entry) {
@@ -1791,6 +1797,8 @@ server_client_loop(void)
 			wp->flags &= ~(PANE_REDRAW|PANE_REDRAWSCROLLBAR|
 			    PANE_ACTIVITY);
 		}
+		redraw_free_damage(w);
+
 		check_window_name(w);
 	}
 
@@ -2336,6 +2344,8 @@ server_client_any_pane_redraw(struct client *c)
 
 	if (c->flags & CLIENT_REDRAWWINDOW)
 		return (1);
+	if (!TAILQ_EMPTY(&w->damage))
+		return (1);
 	TAILQ_FOREACH(wp, &w->panes, entry) {
 		if (wp->flags & (PANE_REDRAW|PANE_REDRAWSCROLLBAR))
 			return (1);
@@ -2352,6 +2362,7 @@ server_client_check_redraw(struct client *c)
 	struct window		*w = s->curw->window;
 	struct window_pane	*wp;
 	int			 needed, tflags, mode = tty->mode;
+	int			 damaged = !TAILQ_EMPTY(&w->damage);
 	struct timeval		 tv = { .tv_usec = 1000 };
 	static struct event	 ev;
 	size_t			 n;
@@ -2377,12 +2388,12 @@ server_client_check_redraw(struct client *c)
 		return;
 	}
 
-	/*
-	 * If there is outstanding data, defer the redraw until it has been
-	 * consumed. We can just add a timer to get out of the event loop and
-	 * end up back here.
-	 */
+	/* Ignore output queued within the current synchronized frame. */
 	n = EVBUFFER_LENGTH(tty->out);
+	if ((tty->flags & TTY_SYNCING) && n > tty->sync_offset)
+		n = tty->sync_offset;
+
+	/* Defer until output drains, preserving damage in client flags. */
 	if (n != 0 || (tty->flags & TTY_BLOCK)) {
 		if (n != 0)
 			log_debug("%s: redraw deferred (%zu left)", c->name, n);
@@ -2394,6 +2405,10 @@ server_client_check_redraw(struct client *c)
 			log_debug("redraw timer started");
 			evtimer_add(&ev, &tv);
 		}
+		if (damaged) {
+			c->flags |= CLIENT_REDRAWWINDOW;
+			return;
+		}
 		TAILQ_FOREACH(wp, &w->panes, entry) {
 			if (wp->flags & PANE_REDRAW) {
 				c->flags |= CLIENT_REDRAWWINDOW;
@@ -2427,6 +2442,10 @@ server_client_check_redraw(struct client *c)
 				redraw_pane_scrollbar(c, wp);
 			}
 		}
+
+		/* Draw damage here if no client redraw flags will handle it. */
+		if (damaged && (c->flags & CLIENT_ALLREDRAWFLAGS) == 0)
+			redraw_client_damage(c);
 	}
 
 	/*
@@ -2440,6 +2459,7 @@ server_client_check_redraw(struct client *c)
 		}
 		server_client_set_progress_bar(c);
 		redraw_screen(c);
+		redraw_client_damage(c);
 	}
 
 	/* Put the tty back how it was. */

tmux.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: tmux.h,v 1.1449 2026/09/28 10:10:16 nicm Exp $ */
+/* $OpenBSD: tmux.h,v 1.1451 2026/10/02 12:48:52 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -69,6 +69,7 @@ struct options_array_item;
 struct options_entry;
 struct prompt;
 struct window_pane_prompt;
+struct redraw_damage;
 struct redraw_scene;
 struct redraw_span;
 struct screen_write_citem;
@@ -1406,6 +1407,7 @@ struct window_pane {
 	struct screen	 base;
 
 	struct screen	 status_screen;
+	u_int		 status_generation;
 
 	TAILQ_HEAD(, window_mode_entry) modes;
 
@@ -1436,6 +1438,7 @@ struct window_pane {
 TAILQ_HEAD(window_panes, window_pane);
 TAILQ_HEAD(window_panes_zindex, window_pane);
 RB_HEAD(window_pane_tree, window_pane);
+TAILQ_HEAD(redraw_damages, redraw_damage);
 
 /* Window structure. */
 struct window {
@@ -1479,6 +1482,9 @@ struct window {
 
 	uint64_t		 redraw_scene_generation;
 
+	struct redraw_damages	 damage;
+	u_int			 damage_count;
+
 	struct menu_data	*menu;
 	u_int			 menu_last_px;
 	u_int			 menu_last_py;
@@ -1804,6 +1810,8 @@ struct tty {
 	struct event	 timer;
 	size_t		 discarded;
 
+	size_t		 sync_offset;
+
 	struct termios	 tio;
 
 	struct grid_cell cell;
@@ -1851,7 +1859,7 @@ struct tty {
 };
 
 /* Terminal command context. */
-typedef void (*tty_ctx_redraw_cb)(const struct tty_ctx *);
+typedef void (*tty_ctx_redraw_cb)(const struct tty_ctx *, u_int, u_int);
 typedef int (*tty_ctx_set_client_cb)(struct tty_ctx *, struct client *);
 struct tty_ctx {
 	struct screen		*s;
@@ -2611,6 +2619,7 @@ extern char **cfg_files;
 extern u_int cfg_nfiles;
 extern int cfg_quiet;
 void	start_cfg(void);
+void	cfg_client_lost(struct client *);
 int	load_cfg(const char *, struct client *, struct cmdq_item *,
             struct cmd_find_state *, int, struct cmdq_item **);
 int	load_cfg_from_buffer(const void *, size_t, const char *,
@@ -3638,8 +3647,12 @@ void	 redraw_screen(struct client *);
 void	 redraw_pane(struct client *, struct window_pane *);
 void	 redraw_pane_scrollbar(struct client *, struct window_pane *);
 void	 redraw_free_scene(struct redraw_scene *);
+int	 redraw_client_has_window(struct client *, struct window *);
 void	 redraw_invalidate_scene(struct window *);
 void	 redraw_invalidate_all_scenes(void);
+void	 redraw_damage_window(struct window *, u_int, u_int, u_int, u_int);
+void	 redraw_free_damage(struct window *);
+void	 redraw_client_damage(struct client *);
 int	 redraw_get_status_border_cell_type(struct redraw_span **, u_int);
 
 /* screen.c */
@@ -3816,6 +3829,8 @@ struct style_range *window_pane_status_get_range(struct window_pane *, u_int,
 		     u_int);
 int		 window_pane_is_floating(struct window_pane *);
 int		 window_pane_is_floating_with_hidden(struct window_pane *);
+void		 window_redraw_floating_pane(struct window_pane *, int, int,
+		     int, int);
 
 /* window-border.c */
 void		 window_set_fill_cells(struct window *);

tty.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: tty.c,v 1.482 2026/09/22 06:58:06 nicm Exp $ */
+/* $OpenBSD: tty.c,v 1.483 2026/10/02 12:48:52 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -1115,7 +1115,7 @@ tty_redraw_region(struct tty *tty, const struct tty_ctx *ctx)
 	 */
 	if (tty_large_region(tty, ctx) || ctx->flags & TTY_CTX_PANE_OBSCURED) {
 		log_debug("%s: %s large region redraw", __func__, c->name);
-		ctx->redraw_cb(ctx);
+		ctx->redraw_cb(ctx, ctx->orupper, ctx->orlower - ctx->orupper + 1);
 		return;
 	}
 
@@ -1517,6 +1517,7 @@ tty_sync_start(struct tty *tty)
 	if (tty->flags & TTY_SYNCING)
 		return;
 	tty->flags |= TTY_SYNCING;
+	tty->sync_offset = EVBUFFER_LENGTH(tty->out);
 
 	if (tty_term_has(tty->term, TTYC_SYNC)) {
 		log_debug("%s sync start", tty->client->name);
@@ -1923,7 +1924,7 @@ tty_cmd_alignmenttest(struct tty *tty, const struct tty_ctx *ctx)
 	u_int		 i, j;
 
 	if (ctx->flags & TTY_CTX_WINDOW_BIGGER) {
-		ctx->redraw_cb(ctx);
+		ctx->redraw_cb(ctx, 0, ctx->sy);
 		return;
 	}
 
@@ -1982,7 +1983,7 @@ tty_cmd_cells(struct tty *tty, const struct tty_ctx *ctx)
 		    tty->cy == tty->rlower)
 			tty_draw_pane(tty, ctx, ctx->ocy);
 		else
-			ctx->redraw_cb(ctx);
+			ctx->redraw_cb(ctx, ctx->ocy, 1);
 		return;
 	}
 

window-copy.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: window-copy.c,v 1.431 2026/09/21 10:43:37 nicm Exp $ */
+/* $OpenBSD: window-copy.c,v 1.432 2026/10/02 12:48:52 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -768,6 +768,7 @@ window_copy_scroll(struct window_pane *wp, int sl_mpos, u_int my,
 	struct window_mode_entry	*wme = TAILQ_FIRST(&wp->modes);
 
 	if (wme != NULL) {
+		window_redraw_active_switch(wp->window, wp);
 		window_set_active_pane(wp->window, wp, 0);
 		window_copy_scroll1(wme, wp, sl_mpos, my, tty_oy, scroll_exit);
 	}

window.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: window.c,v 1.383 2026/09/28 10:42:01 nicm Exp $ */
+/* $OpenBSD: window.c,v 1.384 2026/10/02 12:48:52 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -423,6 +423,7 @@ window_create(u_int sx, u_int sy, u_int xpixel, u_int ypixel)
 	TAILQ_INIT(&w->panes);
 	TAILQ_INIT(&w->z_index);
 	TAILQ_INIT(&w->last_panes);
+	TAILQ_INIT(&w->damage);
 	w->active = NULL;
 
 	w->lastlayout = -1;
@@ -476,6 +477,7 @@ window_destroy(struct window *w)
 
 	menu_destroy(w);
 	window_destroy_panes(w);
+	redraw_free_damage(w);
 
 	if (event_initialized(&w->name_event))
 		evtimer_del(&w->name_event);
@@ -754,6 +756,7 @@ int
 window_set_active_pane(struct window *w, struct window_pane *wp, int notify)
 {
 	struct window_pane *lastwp;
+	int		    unzoomed;
 
 	log_debug("%s: pane %%%u", __func__, wp->id);
 
@@ -761,7 +764,8 @@ window_set_active_pane(struct window *w, struct window_pane *wp, int notify)
 		return (0);
 	if (w->modal != NULL && wp != w->modal)
 		return (0);
-	if ((w->flags & WINDOW_ZOOMED) && !window_pane_is_visible(wp))
+	unzoomed = (w->flags & WINDOW_ZOOMED) && !window_pane_is_visible(wp);
+	if (unzoomed)
 		window_unzoom(w, 1);
 	lastwp = w->active;
 
@@ -778,7 +782,19 @@ window_set_active_pane(struct window *w, struct window_pane *wp, int notify)
 	}
 
 	tty_update_window_offset(w);
-	server_redraw_window(w);
+
+	/*
+	 * Unzooming changes every pane's geometry and needs a full window
+	 * redraw. Otherwise, only the previous and new active pane's border
+	 * and status appearance changed, so avoid redrawing unaffected pane
+	 * content.
+	 */
+	if (unzoomed)
+		server_redraw_window(w);
+	else {
+		server_redraw_window_borders(w);
+		server_status_window(w);
+	}
 
 	if (notify)
 		window_fire_pane_changed(w, w->active, lastwp);
@@ -2971,3 +2987,40 @@ window_pane_is_floating_with_hidden(struct window_pane *wp)
 		return (0);
 	return (1);
 }
+
+/* Report damage for a floating pane, including its border and scrollbar. */
+static void
+window_damage_floating_pane(struct window_pane *wp, int xoff, int yoff,
+    int sx, int sy)
+{
+	struct window	*w = wp->window;
+	int		 x0, x1, y0, y1, sb_left = 0, sb_right = 0;
+	struct style	*sb_sy = &wp->scrollbar_style;
+
+	if (window_pane_scrollbar_reserve(wp)) {
+		if (w->sb_pos == PANE_SCROLLBARS_LEFT)
+			sb_left = sb_sy->width + sb_sy->pad;
+		else
+			sb_right = sb_sy->width + sb_sy->pad;
+	}
+	x0 = xoff - 1 - sb_left;
+	x1 = xoff + sx + sb_right;
+	y0 = yoff - 1;
+	y1 = yoff + sy;
+	if (x0 < 0)
+		x0 = 0;
+	if (y0 < 0)
+		y0 = 0;
+	if (x1 >= x0 && y1 >= y0)
+		redraw_damage_window(w, x0, y0, x1 - x0 + 1U, y1 - y0 + 1U);
+}
+
+/* Report damage for a floating pane's old and new areas. */
+void
+window_redraw_floating_pane(struct window_pane *wp, int oxoff, int oyoff,
+    int osx, int osy)
+{
+	window_damage_floating_pane(wp, oxoff, oyoff, osx, osy);
+	window_damage_floating_pane(wp, wp->xoff, wp->yoff, wp->sx, wp->sy);
+	server_status_window(wp->window);
+}