A column has a ctl, an exec and an rmdir over 9P, and Restore maps its serial

A script could read and write a column's tag but not act on the column.
col/<serial>/ctl takes Delcol, Joincol, New and Tty, each acting on that
column as from its tag; col/<serial>/exec runs a word as a middle click in
the tag; rmdir col/<serial> closes an empty column and refuses one with
panes (ENOTEMPTY, an err record saying why). The root ctl's refusal of
Delcol and Joincol points at col/<serial>/ctl. A dump keeps each column's
serial and Restore logs restoredcol <old> <new>; the dump golden gains
them. Documented: Joincol's survivor, the column on the right, keeps its
serial and tag.

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

1 files changed, 11 insertions, 2 deletions

diff --git a/docs/fs.md b/docs/fs.md
index a4fec333..46fe9f86 100644
--- a/docs/fs.md
+++ b/docs/fs.md
@@ -111,6 +111,9 @@ Existing Plan9port/v9fs clients need a userspace bridge for QUIC.
              pane/new and a look place a pane next (- when there is none)
 /tag         the workspace tag; > replaces it, >> appends, one line
 /col/<n>/tag the tag of the column with serial n, the same way
+/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; 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
              64 panes (16 on the board); at that, every route that would open one -- this
              open, look, exec, New, Tty -- fails with `no pane slots: 64 max` and an err
@@ -130,7 +133,12 @@ clears it and drops the newline that ends it, as a pane tag's does. A
 column is named by its serial, as a pane is: it stays while the column
 lives, whatever opens or closes beside it, and is never reused; /layout
 gives each column's serial and its index left to right, and the log says
-`newcol <serial>` and `delcol <serial>` as columns come and go.
+`newcol <serial>` and `delcol <serial>` as columns come and go, and after a
+Restore `restoredcol <old> <new>` for each column as `restored` does for
+panes. Joincol folds a column into the one on its right, which keeps its own
+serial and tag; the joined one's serial is gone (`delcol`). The root ctl
+takes no column word: its `Delcol` is refused, pointing at
+`col/<serial>/ctl`.
 
 Control messages are split by what they act on, as acme keeps window verbs
 on a window's ctl and webfs and upas/fs keep session settings on a root ctl.
@@ -563,7 +571,8 @@ the `del` of a terminal whose shell exited by itself, `ask <serial> <what>
 and `save <serial> <name>`,
 `dump <path>` when a Dump is written and `restore <path>` in a Restore's
 new log after its panes' `new`s, then `restored <old> <new>` for each pane,
-mapping the serial it had to the one it has now, and `msg <serial|-> <text>`
+mapping the serial it had to the one it has now, and `restoredcol <old>
+<new>` for each column, and `msg <serial|-> <text>`
 for every line the editor says, repeats included (with `verbose` on, that
 includes each builtin announcing itself as it runs, on purpose: the log says
 which ran; its serial is the pane it ran at, `-` when the keyboard was on a