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, 12 insertions, 9 deletions

diff --git a/src/tutor.txt b/src/tutor.txt
index 394a48a3..adf4ae3a 100644
--- a/src/tutor.txt
+++ b/src/tutor.txt
@@ -160,8 +160,10 @@
 
  RAW INPUT
  Ctrl-b switches to editor mode. Other keys go to the child,
- including Ctrl-o, Ctrl-w, Ctrl-V, Ctrl-Shift-V, Alt shortcuts, and
- modified Escape. Plain Esc at a detected shell prompt hops
+ including Ctrl-o, Ctrl-w, Alt shortcuts, and
+ modified Escape. The two paste chords are the exception: Ctrl-V
+ types the yank register at the program and Ctrl-Shift-V types the
+ desktop clipboard. Plain Esc at a detected shell prompt hops
  to the previous pane. While a program owns the terminal, Esc goes
  to that program too. Use the Togglettymode tag to leave raw input
  in place. Desktop paste events still feed the child.
@@ -387,15 +389,15 @@ typed
 
    pardes          the 9P socket opens by default
 
- A directory per pane holding `name`, `body`, `tag`, `ctl`, `addr`,
- `data`, `sel`, `event`, `pty/` and the rest, plus `index`, `ctl`,
- `new` and `log` at the root. Every pane shell receives `$PARDES_9P`
- (the socket) and `$PARDES_PANE` (its serial). Use a 9P client:
+ A directory per pane holding `name`, `body`, `tag`, `addr`, `dot`,
+ `data`, `sel`, `dirty`, `event`, `pty/` and the rest, plus `index`,
+ `status`, `look`, `exec` and `log` at the root. Every pane shell
+ receives `$PARDES_9P` (the socket) and `$PARDES_PANE` (its serial):
 
      /pane/<serial>/body
      /index
-     /new                     reading it makes a pane, answers its serial
-     /ctl                     `look FILE:12` and `exec Save`, as the mouse does
+     /pane                    mkdir here makes a pane, rmdir closes it
+     /look   /exec            `FILE:12` and `Save`, as the mouse does
 
  A terminal pane also has `pty/`:
 
@@ -446,7 +448,8 @@ typed
             Esc goes to the program — except at a shell PROMPT, where
                 it hops to the previous pane
             Ctrl-b switches to editor mode
-            All other keys belong to the child, including Ctrl-V
+            Ctrl-V types the register, Ctrl-Shift-V the clipboard
+            All other keys belong to the child
 
  DETACHED   pardes --detach[=name]     the core, no terminal
             pardes --attach[=name]     a frontend for it