A new pane with no room under the last goes last all the same

A pane from pane/new or New takes the bottom half of its column's last
pane, as acme's coladd does (cols.c:62-65); when that pane is too short
to give it a tag and 2 rows, the fallback halved the tallest pane and
put the new one under it, mid-column (the 7 9 8 found). It now goes last
all the same, with half the tallest pane's rows (its tag measured at the
column's width). Tty from a pane's ctl already follows acme's
makenewwindow (the active column first, util.c:456-467); fs.md now says
so rather than beside that pane.

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

1 files changed, 7 insertions, 2 deletions

diff --git a/docs/fs.md b/docs/fs.md
index 45a64e44..5c2486f4 100644
--- a/docs/fs.md
+++ b/docs/fs.md
@@ -124,7 +124,9 @@ Existing Plan9port/v9fs clients need a userspace bridge for QUIC.
 /col/<n>/ctl write Delcol, Joincol, New or Tty: each acts on that column, as from its tag
 /col/<n>/exec write a word: a middle click on it in that column's tag; read as /exec; rmdir col/<n> closes
              an empty column (a column with panes is refused, ENOTEMPTY)
-/pane/new    open it to make a pane; the read answers that pane's serial. A session holds
+/pane/new    open it to make a pane (the bottom half of the active column's last
+             pane, acme's coladd; with no room there, last all the same, taking half
+             the tallest pane's rows); the read answers that pane's serial. A session holds
              64 panes (16 on the board); at that, every route that would open one -- this
              open, look, exec, New, Tty -- fails with `no space for a pane: 64 max` (ENOSPC through 9ns, which has
              no word for ENFILE) and an err
@@ -327,7 +329,10 @@ same tree without leaving the process.
   `src/builtins.zig` (`Save`, `Del`, `New`, `Newcol`, `Mount NAME DIAL`,
   `Unmount NAME`, `Dump`, `Restore`, `Msg TEXT`, `Find`, `Grep`, `Tty`, ...;
   `Tty`'s argument is the shell it runs, `Tty fish`, and `Tty` on a pane's
-  ctl opens a new terminal pane beside that one, not in it),
+  ctl opens a new terminal pane, not in that one: in the active column, as
+  acme's makenewwindow puts a new window (util.c:456-467: the active column
+  first, then the pane's own), under the text with room or halving the
+  tallest, never shorter than its tag and 2 rows),
   or anything else, a command line. Written at a terminal at its prompt it
   is typed into that shell (and a terminal whose shell exits, `exit` typed
   or run, closes its pane). From anywhere else -- a file, a scratch, a tag,