Add a feature for mintty's application escape to avoid dodgy terminals

whinging about not supporting it, GitHub issue 5626 from Pete Dietl.

tmux.1

@@ -1,4 +1,4 @@
-.\" $OpenBSD: tmux.1,v 1.1171 2026/09/21 10:22:31 nicm Exp $
+.\" $OpenBSD: tmux.1,v 1.1172 2026/09/22 06:58:05 nicm Exp $
 .\"
 .\" Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
 .\"
@@ -14,7 +14,7 @@
 .\" IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 .\" OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: September 21 2026 $
+.Dd $Mdocdate: September 22 2026 $
 .Dt TMUX 1
 .Os
 .Sh NAME
@@ -5083,6 +5083,9 @@ The available features are:
 .Bl -tag -width Ds
 .It 256
 Supports 256 colours with the SGR escape sequences.
+.It appesc
+Supports application escape key mode, where the Escape key sends a sequence
+that cannot be mistaken for the start of another key.
 .It clipboard
 Allows setting the system clipboard.
 .It ccolour
@@ -8831,6 +8834,8 @@ These are set automatically if the
 capability is present.
 .It Em \&Dseks , \&Eneks
 Disable and enable extended keys.
+.It Em \&Dsesc , \&Enesc
+Disable and enable application escape key mode.
 .It Em \&Dsfcs , \&Enfcs
 Disable and enable focus reporting.
 These are set automatically if the

tmux.h

@@ -1,4 +1,4 @@
-/* $OpenBSD: tmux.h,v 1.1445 2026/09/22 06:46:50 nicm Exp $ */
+/* $OpenBSD: tmux.h,v 1.1446 2026/09/22 06:58:06 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -455,6 +455,7 @@ enum tty_code_code {
 	TTYC_DL1,
 	TTYC_DSBP,
 	TTYC_DSEKS,
+	TTYC_DSESC,
 	TTYC_DSFCS,
 	TTYC_DSMG,
 	TTYC_E3,
@@ -465,6 +466,7 @@ enum tty_code_code {
 	TTYC_ENACS,
 	TTYC_ENBP,
 	TTYC_ENEKS,
+	TTYC_ENESC,
 	TTYC_ENFCS,
 	TTYC_ENMG,
 	TTYC_FSL,

tty-features.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: tty-features.c,v 1.43 2026/08/31 12:41:03 kirill Exp $ */
+/* $OpenBSD: tty-features.c,v 1.44 2026/09/22 06:58:06 nicm Exp $ */
 
 /*
  * Copyright (c) 2020 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -179,6 +179,18 @@ static const struct tty_feature tty_feature_focus = {
 	0
 };
 
+/* Terminal supports application escape key mode. */
+static const char *const tty_feature_appesc_capabilities[] = {
+	"Enesc=\\E[?7727h",
+	"Dsesc=\\E[?7727l",
+	NULL
+};
+static const struct tty_feature tty_feature_appesc = {
+	"appesc",
+	tty_feature_appesc_capabilities,
+	0
+};
+
 /* Terminal supports cursor styles. */
 static const char *const tty_feature_cstyle_capabilities[] = {
 	"Ss=\\E[%p1%d q",
@@ -368,6 +380,7 @@ static const struct tty_feature tty_feature_utf8 = {
 /* Available terminal features. */
 static const struct tty_feature *const tty_features[] = {
 	&tty_feature_256,
+	&tty_feature_appesc,
 	&tty_feature_bpaste,
 	&tty_feature_ccolour,
 	&tty_feature_clipboard,
@@ -558,6 +571,7 @@ tty_default_features(struct client *c, const char *name, u_int version)
 	"256,RGB,bpaste,clipboard,mouse,strikethrough,title"
 		{ .name = "mintty",
 		  .features = TTY_FEATURES_BASE_MODERN_XTERM ","
+			      "appesc,"
 			      "ccolour,"
 			      "cstyle,"
 			      "extkeys,"

tty-term.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: tty-term.c,v 1.109 2026/08/25 08:37:08 nicm Exp $ */
+/* $OpenBSD: tty-term.c,v 1.110 2026/09/22 06:58:06 nicm Exp $ */
 
 /*
  * Copyright (c) 2008 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -87,6 +87,7 @@ static const struct tty_term_code_entry tty_term_codes[] = {
 	[TTYC_DL1] = { TTYCODE_STRING, "dl1" },
 	[TTYC_DL] = { TTYCODE_STRING, "dl" },
 	[TTYC_DSEKS] = { TTYCODE_STRING, "Dseks" },
+	[TTYC_DSESC] = { TTYCODE_STRING, "Dsesc" },
 	[TTYC_DSFCS] = { TTYCODE_STRING, "Dsfcs" },
 	[TTYC_DSBP] = { TTYCODE_STRING, "Dsbp" },
 	[TTYC_DSMG] = { TTYCODE_STRING, "Dsmg" },
@@ -98,6 +99,7 @@ static const struct tty_term_code_entry tty_term_codes[] = {
 	[TTYC_ENACS] = { TTYCODE_STRING, "enacs" },
 	[TTYC_ENBP] = { TTYCODE_STRING, "Enbp" },
 	[TTYC_ENEKS] = { TTYCODE_STRING, "Eneks" },
+	[TTYC_ENESC] = { TTYCODE_STRING, "Enesc" },
 	[TTYC_ENFCS] = { TTYCODE_STRING, "Enfcs" },
 	[TTYC_ENMG] = { TTYCODE_STRING, "Enmg" },
 	[TTYC_FSL] = { TTYCODE_STRING, "fsl" },

tty.c

@@ -1,4 +1,4 @@
-/* $OpenBSD: tty.c,v 1.481 2026/09/21 10:22:31 nicm Exp $ */
+/* $OpenBSD: tty.c,v 1.482 2026/09/22 06:58:06 nicm Exp $ */
 
 /*
  * Copyright (c) 2007 Nicholas Marriott <nicholas.marriott@gmail.com>
@@ -497,8 +497,7 @@ tty_stop_tty(struct tty *tty)
 	if (tty_term_has(tty->term, TTYC_DSBP))
 		tty_raw(tty, tty_term_string(tty->term, TTYC_DSBP));
 
-	if (tty->term->flags & TERM_VT100LIKE)
+	tty_raw(tty, tty_term_string(tty->term, TTYC_DSESC));
-		tty_raw(tty, "\033[?7727l");
 	tty_raw(tty, tty_term_string(tty->term, TTYC_DSFCS));
 	tty_raw(tty, tty_term_string(tty->term, TTYC_DSEKS));
 
@@ -555,8 +554,7 @@ tty_update_features(struct tty *tty)
 		tty_puts(tty, tty_term_string(tty->term, TTYC_ENEKS));
 	if (options_get_number(global_options, "focus-events"))
 		tty_puts(tty, tty_term_string(tty->term, TTYC_ENFCS));
-	if (tty->term->flags & TERM_VT100LIKE)
+	tty_puts(tty, tty_term_string(tty->term, TTYC_ENESC));
-		tty_puts(tty, "\033[?7727h");
 
 	/*
 	 * Features might have changed since the first draw during attach. For