No placement leaves a pane shorter than its tag and two rows

Placement could split a pane down to a tag and one row, or give a new one
less. Every placement now checks the pane it made and each pane it shrank
against its tag (wrapped at its width) plus two rows: where they lack the
room, the column's tallest pane is halved instead, and where none can give
it the new pane is refused with "no space for a pane in that column"
(ENOSPC over 9P) and closed at the step's end, once its maker is done with
it. splitBelow and splitParent leave two body rows (a boot layout, split
before any row exists, is as before). Re-recorded by name: lookpanes (panes
one or two rows lower) and splitparent (the 6-row squeeze now refuses);
fs.py closes the scratches and long-named panes it no longer needs, since
its 24-row session filled.

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 95ab4de0..e81ea18d 100644
--- a/docs/fs.md
+++ b/docs/fs.md
@@ -119,7 +119,9 @@ Existing Plan9port/v9fs clients need a userspace bridge for QUIC.
              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
-             record, and look reads back empty
+             record, and look reads back empty; a column with no rows left for one
+             (each pane keeps its tag and 2 rows) refuses it the same way,
+             `no space for a pane in that column` (docs/tags.md)
 /pane/<n>/   name body tag ctl addr dot limit data xdata sel dirty mark scroll
              errors event look exec, plus pty/{ctl,status,data} on terminals
 /os/         the host filesystem