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.

tmux.1

@@ -4914,19 +4914,29 @@ If enabled, the server will exit when there are no attached clients.
 .Op Ic on | off | always
 .Xc
 Controls how modified keys are reported.
-For the
-.Ic csi\-u
-and
-.Ic xterm
-formats, this controls the
+When enabled,
+.Nm
+uses the Kitty keyboard protocol with terminals which support it, and the
 .Ic modifyOtherKeys
 .Xr xterm 1
-resource.
-For the
-.Ic kitty
-format, this controls the progressive keyboard protocol enhancements.
+resource with other terminals which support extended keys.
+Each client uses the best that its terminal supports, so clients with different
+terminals may be attached at the same time.
 .Pp
-When set to
+Programs inside panes may request either the Kitty keyboard protocol or
+.Ic modifyOtherKeys ,
+and keys are sent to each program in the form it requested, whichever client
+they were typed on.
+The Kitty keyboard protocol can report the Super and Hyper modifiers, whose key
+name prefixes are
+.Ql s-
+and
+.Ql H- ;
+its disambiguate and report-all enhancements are supported.
+.Pp
+For
+.Ic modifyOtherKeys ,
+when set to
 .Ic on ,
 the program inside the pane can request one of two modes: mode 1 which changes
 the sequence for only keys which lack an existing well-known representation; or
@@ -4935,7 +4945,8 @@ When set to
 .Ic always ,
 modes 1 and 2 can still be requested by applications, but mode 1 will be forced
 instead of the standard mode.
-This applies only to applications inside panes and does not change what
+This applies only to applications inside panes; it does not force the Kitty
+keyboard protocol or change what
 .Nm
 requests from the terminal.
 When set to
@@ -4944,19 +4955,12 @@ this feature is disabled and only standard keys are reported.
 .Pp
 .Nm
 will always request extended keys itself if the terminal supports them.
-When the
-.Ic kitty
-format is selected, it is preferred separately for each client; clients which
-do not support it use standard extended keys if available, or standard VT10x
-keys otherwise.
-Input from standard extended-key clients is translated to Kitty encoding for
-applications which have requested it.
-A Kitty keyboard state query reflects the clients attached to the window at
-the time of the query; if none are attached, the requested state is reported.
-Applications are not notified if client support changes after the reply.
+Support for the Kitty keyboard protocol is detected when a client attaches.
 See also the
+.Ic kittykeys
+and
 .Ic extkeys
-feature for the
+features for the
 .Ic terminal\-features
 option, the
 .Ic extended\-keys\-format
@@ -4968,22 +4972,9 @@ variables.
 .It Xo Ic extended\-keys\-format
 .Op Ic csi\-u | xterm | kitty
 .Xc
-Selects the format for reporting modified keys to applications.
-The
-.Ic kitty
-format uses the Kitty keyboard protocol and supports the Super and Hyper
-modifiers.
-Their key name prefixes are
-.Ql s-
-and
-.Ql H- .
-The disambiguate and report-all enhancements are supported; event types,
-alternate keys and associated text are not requested.
-For the
-.Ic csi\-u
-and
-.Ic xterm
-formats, this is the equivalent of the
+Selects the format for reporting modified keys to programs which request
+.Ic modifyOtherKeys .
+This is the equivalent of the
 .Ic formatOtherKeys
 .Xr xterm 1
 resource.
@@ -4995,10 +4986,11 @@ and as
 .Ql \[ha][[65;6u
 when set to
 .Ic csi\-u .
-With
-.Ic kitty ,
-it will be reported as
-.Ql \[ha][[97;6u .
+.Ic kitty
+is accepted for compatibility and is the same as
+.Ic csi\-u ;
+programs which request the Kitty keyboard protocol receive it whatever this
+option is set to.
 .It Xo Ic focus\-events
 .Op Ic on | off
 .Xc
@@ -5150,6 +5142,9 @@ Ignore function keys from
 and use the
 .Nm
 internal set only.
+.It kittykeys
+Supports the Kitty keyboard protocol.
+This is added automatically if the terminal answers the Kitty keyboard query.
 .It margins
 Supports DECSLRM margins.
 .It mouse