pty/status reads the pty's size as winsize set it, on a line of its own

A dogfood agent wrote winsize 100 30 to pty/ctl and pty/status went on
reporting the pane's grid, and the status line had no newline to end it.
The size winsize sets is kept until the pane resizes and gives the pty its
grid again; ctl's winsize read back and status both report it, and status
ends with a newline.

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

1 files changed, 5 insertions, 1 deletions

diff --git a/docs/fs.md b/docs/fs.md
index a489e1ea..29f15571 100644
--- a/docs/fs.md
+++ b/docs/fs.md
@@ -563,7 +563,11 @@ command whose end mark carried no status, which is not a success; `error out
 of memory` is an answer that could not be made. The header is always the
 whole first line. It reads
 `busy` at once when a command is running or text is typed at the prompt,
-which is also when the third field of `pty/status` reads 1. A line written
+which is also when the third field of `pty/status` reads 1. `pty/status` is
+one line, three right-aligned fields and a newline: the pty's columns and
+rows, then busy (0 or 1). The size, and `pty/ctl`'s `winsize` read back, is
+what `winsize C R` last set, until the pane itself resizes and gives the pty
+its grid again. A line written
 before a new terminal's shell has drawn its first prompt is not busy: it
 waits for that prompt (a respawn meanwhile keeps it waiting for the new
 shell's) and is sent then, so the first command a script gives a fresh