A detached session with no frontend takes its size from the root ctl

A --detach session nobody is attached to stayed 80x24, too small for an
agent's panes, and nothing could change it. The root ctl takes size <cols>
<rows> while no frontend is attached (refused while one owns the size), and
a client that attaches later still sets its own (the server compares with
the core's size). Documented with the 80x24 default.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 3 insertions, 1 deletions

diff --git a/docs/fs.md b/docs/fs.md
index e9dfac65..80735642 100644
--- a/docs/fs.md
+++ b/docs/fs.md
@@ -104,7 +104,9 @@ Existing Plan9port/v9fs clients need a userspace bridge for QUIC.
 /listeners   the session's dial addresses
 /focus       the serial of the pane with the keyboard; write a serial to give it the keyboard,
              which makes its column the active one as a click there would
-/ctl         the settings, one a line as a write takes them; write a setting or a session builtin
+/ctl         the settings, one a line as a write takes them; write a setting or a session builtin;
+             `size <cols> <rows>` sets the screen of a session no frontend is attached to
+             (`--detach`, 80x24 until then; refused while a frontend owns the size)
 /commands    every builtin: word, `arg` if it takes one, `root` or `pane` (the ctl that takes it), a setting's values
 /layout      one line per column, left to right: serial index x width current|notcurrent
              empty|full pane-serials...; then active <serial>: the active column, where