Plan 9 idiom for the control filesystem, and the regressions a624a56 left

The 9P tree stops being a command language wearing a filesystem. /new
created a pane as a side effect of a *read*; it is now Tcreate in /pane,
with Tremove to close, which cloud9's engine has always supported and the
editor never declared: tree.zig now says
`features = .{ .create = true, .remove = true }`. Eleven pane ctl verbs
become files that can be read as well as written -- dot, limit, dirty,
mark, scroll, look, exec -- leaving ctl with `get`, the one verb no file
would say better. Root /ctl splits into a read-only /status and the
/look and /exec files whose write IS the click. stat carries real sizes
where it used to answer 0, and qid versions track a pane's revision, so a
client can poll for change without re-reading the body.

Commit a624a56 moved raw-tty keys to an early-return branch that knew only
Ctrl-B and bare Escape, and in the same edit deleted the paste branch below
it. That cost Shift-Escape (the unconditional way out of tty mode) and both
paste chords: Ctrl-V and Ctrl-Shift-V reached the child as keystrokes, so an
agent CLI running in a pane took Ctrl-V for its image-paste binding and
answered "No image found in clipboard". Both are restored, with tests.

Nested detection was not subtly broken but deleted: 60367d8 removed
nested.zig's process-ancestry walk and left "am I inside pardes" derived from
PARDES_FORWARD_LOOK, which read "0" both for --nested and for "the listener
did not come up". PARDES_PID now answers that question on its own, checked
with kill(pid, 0); PARDES_9P and PARDES_PANE answer how to reach it; the flag
is gone. The posted-9P registry also self-heals now -- a session that aborts
cannot unlink its own socket, so posting sweeps entries whose target refuses
a connection, symlinks only and on a definite ECONNREFUSED only.

Elsewhere: tty scrolling is sticky-bottom, following new output only from
the last row, with typing and entering raw mode snapping back to live; the
boot layouts are a Boot enum instead of a chain of ifs, and the bare tty
startup (Boot.tty, which main.zig names) opens an empty text pane under the
shell while tests keep Boot.tty_shell; builtins announce themselves on the
message row under a Verbose setting that is on by default; Config prints
each setting the way you would type it back, so WindowOpacity 70 rather than
"WindowOpacity: 70%"; LocationsConfig opens its window only when called bare;
every tagline puts the word that closes the thing last, and a column now
outlives its panes -- closing the last one leaves an empty pane, and only
Delcol, newly on the column tagline, takes the column away.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

1 files changed, 22 insertions, 20 deletions

diff --git a/src/fs-help.txt b/src/fs-help.txt
index a0a84b28..1e5d64c2 100644
--- a/src/fs-help.txt
+++ b/src/fs-help.txt
@@ -2,41 +2,43 @@ Pardes control filesystem
 =========================
 README      this guide
 index       one line per pane: serial, kind (text|term|pdf|image), dirty flag, name
-ctl         write commands; read the serials the last command made or touched
-new         reading it creates one empty pane and answers its serial
+status      pid, version and pane count
+look        write a line: a right click on it at the active pane; read: the serials it touched
+exec        write a line: a middle click, an editor command word or a shell line; read the same
 log         one line per editor event (new/del/rename/save <serial> <name>); reads wait
 screen      rendered screen as JSON, frozen from open to close
 listeners   the session's dial addresses
-pane/<n>/   name body tag ctl addr data xdata sel errors event, and pty/ for terminals
+pane/       mkdir makes a pane, rmdir <serial> closes it
+pane/<n>/   name body tag ctl addr dot limit data xdata sel dirty mark scroll
+            errors event look exec, and pty/ for terminals
 os/         the host filesystem
 src/        the editor's own sources, only in a -Dembed-sources=true build
 
-Commands, on /ctl (applied at the active pane) or on pane/<n>/ctl (at that pane):
-  look TEXT   a right click: open a file, a file:12 location, a directory, a URL
-  exec TEXT   a middle click: an editor command word (Save Del New Newcol Mount Unmount
-              Dump Restore Msg Find Grep Tty ...), or a shell command for the pane's terminal
 Below, $m is the mount point (PARDES_MOUNT in a Tty9p shell; 9ns and 9p work too):
 
   cat $m/index                                 which panes exist
-  n=$(cat $m/new)                              make a pane, remember its serial
-  echo 'look /etc/hosts:3' > $m/ctl; cat $m/ctl   open a file, see the pane it went to
-  printf 'text\n' > $m/pane/$n/body             append to a pane (>| truncates first)
+  mkdir $m/pane/x; n=$(awk 'END{print $1}' $m/index)   make a pane, take its serial
+  echo /etc/hosts:3 > $m/look; cat $m/look     open a file, see the pane it went to
+  printf 'text\n' > $m/pane/$n/body            append to a pane (>| truncates first)
   cat $m/pane/$n/name; echo notes.txt > $m/pane/$n/name        read, then rename
-  echo 'exec Save' > $m/pane/$n/ctl         save it (exec Del closes it)
-  echo 'exec Msg hello' > $m/ctl                show text in the editor
+  echo Save > $m/pane/$n/exec                  save it; rmdir $m/pane/$n closes it
+  echo 'Msg hello' > $m/exec                   show text in the editor
   echo '#0,#5' > $m/pane/$n/addr; echo NEW > $m/pane/$n/data   replace bytes 0..5
-  echo 'dot=addr' > $m/pane/$n/ctl; cat $m/pane/$n/sel   select the range, read it
+  cp $m/pane/$n/addr $m/pane/$n/dot; cat $m/pane/$n/sel   select the range, read it
+  cat $m/pane/$n/dirty; echo 0 > $m/pane/$n/dirty         is it modified? say it is not
   cat $m/log                                   block until a pane is made, renamed, saved or closed
   cat $m/pane/$n/event                         hold it open to own that pane's clicks
-  echo 'exec' > $m/pane/$n/pty/ctl             restart a shell; also winsize C R, sig INT
+  echo exec > $m/pane/$n/pty/ctl               restart a shell; also winsize C R, sig INT
 
 Pitfalls, one each:
-  Every open of new makes another pane, so `cat $m/new` twice makes two.
-  ls, stat and find create nothing; reading log, event or pty/data blocks until something happens.
-  exec Del closes a pane even when it is dirty; index shows the dirty flag first.
-  look and exec are lowercase verbs; the words after exec are the editor's capitalized commands.
-  ctl also takes acme's addr verbs (addr=dot dot=addr limit=addr clean dirty get show ...), one per line.
+  Only mkdir in pane/ makes a pane; ls, stat, find and every read create nothing.
+  Panes are named by the serial the editor gives them, not by the name mkdir asked for.
+  rmdir closes a pane even when it is dirty; index and pane/<n>/dirty show the flag.
+  addr, dot and limit read the same pair of offsets they take, so cp between them works.
+  dirty, mark and scroll read "0" or "1" and take "0" or "1"; truncating limit lifts it.
   Writing body appends; open it with truncation to replace; writes are whole UTF-8 sequences.
+  Truncating tag clears the part you may edit; truncating dot or addr empties it.
   A terminal's body is a history snapshot frozen per open; pty/data is the live stream.
   screen is frozen per open handle as well; reopen it for a fresh frame.
-  A command that fails is reported in the editor, not as a write error; a malformed line fails the write.
+  A failing command is reported in the editor, not as a write error; a bad line fails the write.
+  pane/<n>/ctl reads acme's window status line and takes one verb, get, which reloads from disk.