Detection, done like sync:

- ESC[?u goes to every VT100-like terminal at attach, whatever the
  options.
- A reply turns on a new kittykeys terminal feature. Users can force
  it on or off with terminal-features kittykeys, including kittykeys@
  to turn it off.
- Changing extended-keys now takes effect immediately for attached
  clients (options.c).

Use, per client, when extended-keys is on: Kitty for clients that have
kittykeys, modifyOtherKeys for clients with extkeys, VT10x otherwise.

Pane side:

- Applications can request either protocol; Kitty wins if one asks for
  both.
- Each application gets what it asked for, whichever client typed the
  key.
- ESC[?u is answered truthfully.
- The per-client gate is gone. window.c and popup.c are simply
  master's versions again.

extended-keys always is back to its master meaning, forcing
modifyOtherKeys mode 1 only. Forcing Kitty on every program would have
sent bash ESC[97;5u for Ctrl-A.

extended-keys-format kitty is still accepted, but now behaves the same
as csi-u.

regress/kitty-keys-clients.sh

@@ -1,27 +1,23 @@
 #!/bin/sh
 
-# Test per-client keyboard protocol negotiation and pane-side fallback.
+# Test per-client keyboard protocol detection and pane-side encoding.
 
 PATH=/bin:/usr/bin
 TERM=screen
 
 [ -z "$TEST_TMUX" ] && TEST_TMUX=$(readlink -f ../tmux)
 KCONF=$(mktemp)
-UCONF=$(mktemp)
 LCONF=$(mktemp)
 OUT=$(mktemp)
 TMP=$(mktemp)
 SOCKETS="testKmc$$ testKka$$ testKua$$ testKrt$$ testKru$$ testKlq$$ testKlu$$"
 
-printf '%s\n' 'set -g extended-keys on' \
-    'set -g extended-keys-format kitty' >"$KCONF"
-printf '%s\n' 'set -g extended-keys on' \
-    'set -g extended-keys-format csi-u' >"$UCONF"
+printf '%s\n' 'set -g extended-keys on' >"$KCONF"
 printf '%s\n' 'set -g extended-keys off' >"$LCONF"
 
 cleanup()
 {
-	rm -f "$KCONF" "$UCONF" "$LCONF" "$OUT" "$TMP"
+	rm -f "$KCONF" "$LCONF" "$OUT" "$TMP"
 	for socket in $SOCKETS; do
 		$TEST_TMUX -L"$socket" kill-server 2>/dev/null
 	done
@@ -78,16 +74,17 @@ wait_for_client_mode()
 	[ "$(client_mode "$tmux" "$session")" = "$wanted" ]
 }
 
-# A server preferring Kitty must negotiate each client independently.
+# Each client must be negotiated independently. A tmux with extended-keys off
+# stands in for a terminal without Kitty keys, since it does not answer the
+# query.
 M="$TEST_TMUX -LtestKmc$$ -f$KCONF"
 KA="$TEST_TMUX -LtestKka$$ -f$KCONF"
-UA="$TEST_TMUX -LtestKua$$ -f$UCONF"
+UA="$TEST_TMUX -LtestKua$$ -f$LCONF"
 $M new-session -d -x80 -y24 -s kitty || exit 1
 $M new-session -d -x80 -y24 -s csiu || exit 1
 $KA new-session -d -x80 -y24 "$M attach-session -t kitty" || exit 1
 $UA new-session -d -x80 -y24 "$M attach-session -t csiu" || exit 1
 wait_for_mode "$KA" 'Kitty 1' || exit 1
-wait_for_mode "$UA" 'Ext 2' || exit 1
 
 # Each client must report the protocol its own terminal negotiated.
 wait_for_client_mode "$M" kitty 'Kitty 1' || exit 1
@@ -99,7 +96,7 @@ uc=$($M list-clients -F '#{client_name} #{client_session}' |
 $M command-prompt -t"$uc" -k 'display-message -pl "%%"' >"$TMP" &
 pid=$!
 sleep 0.2
-$UA send-keys 'Escape [97;5u'
+$UA send-keys Escape '[97;5u'
 wait "$pid"
 [ "$(tr -d '[:space:]' <"$TMP")" = 'C-a' ] || exit 1
 
@@ -117,11 +114,10 @@ $M kill-server 2>/dev/null
 # Standard extended input must be translated for a Kitty-requesting pane.
 : >"$OUT"
 R="$TEST_TMUX -LtestKrt$$ -f$KCONF"
-RU="$TEST_TMUX -LtestKru$$ -f$UCONF"
+RU="$TEST_TMUX -LtestKru$$ -f$LCONF"
 $R new-session -d -x80 -y24 \
     "stty raw -echo; printf '\033[>1u'; dd bs=1 count=7 2>/dev/null | od -An -v -t x1 >'$OUT'; sleep 5" || exit 1
 $RU new-session -d -x80 -y24 "$R attach-session" || exit 1
-wait_for_mode "$RU" 'Ext 2' || exit 1
 wait_for_client_mode "$R" '' 'Ext' || exit 1
 $RU send-keys C-a
 wait_for_output "$OUT" || exit 1
@@ -129,16 +125,22 @@ wait_for_output "$OUT" || exit 1
 $RU kill-server 2>/dev/null
 $R kill-server 2>/dev/null
 
-# Do not report Kitty active when an attached client only supports VT10x.
+# An application is told the Kitty flags it asked for even when a client that
+# only supports VT10x is attached, and keys from that client are encoded as it
+# asked.
 : >"$OUT"
+: >"$TMP"
 printf '%s\n' "set -as terminal-overrides ',*:Eneks@:Dseks@'" >>"$KCONF"
 LQ="$TEST_TMUX -LtestKlq$$ -f$KCONF"
 LU="$TEST_TMUX -LtestKlu$$ -f$LCONF"
 $LQ new-session -d -x80 -y24 \
-    "stty raw -echo; sleep 2; printf '\033[>1u\033[?u'; dd bs=1 count=5 2>/dev/null | od -An -v -t x1 >'$OUT'; sleep 5" || exit 1
+    "stty raw -echo; sleep 2; printf '\033[>1u\033[?u'; dd bs=1 count=5 2>/dev/null | od -An -v -t x1 >'$OUT'; dd bs=1 count=7 2>/dev/null | od -An -v -t x1 >'$TMP'; sleep 5" || exit 1
 $LU new-session -d -x80 -y24 "$LQ attach-session" || exit 1
 wait_for_output "$OUT" || exit 1
-[ "$(tr -d ' \n' <"$OUT")" = '1b5b3f3075' ] || exit 1
+[ "$(tr -d ' \n' <"$OUT")" = '1b5b3f3175' ] || exit 1
 wait_for_client_mode "$LQ" '' 'VT10x' || exit 1
+$LU send-keys C-a
+wait_for_output "$TMP" || exit 1
+[ "$(tr -d ' \n' <"$TMP")" = '1b5b39373b3575' ] || exit 1
 
 exit 0