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, 48 insertions, 0 deletions

diff --git a/features.txt b/features.txt
index 3bfc6967..bee079a7 100644
--- a/features.txt
+++ b/features.txt
@@ -20,3 +20,51 @@ on tty mode the mouse selection works but the pardes selection on that pane shou
 between tty panes without changing the pardes semantics or adding anything extra, just neat tricks like this. Still, you might need to come up with something
 to decrease the number of movements/interactions needed to do simple things like copy and pasting text from a terminal to another.
 
+
+The 9p protocol needs to be simplified and made plan9 idiomatic. Stop leaning on ctl verbs: a name should be the operation. The filesystem should carry more
+in stat metadata (real sizes, mtimes, qid versions so a client can poll for change cheaply) and use the real 9P operations for what is currently a ctl verb or a
+magic read. cloud9's engine already exposes fs.Features{create, remove, wstat} and the editor backend simply never declared them, so /new creating a pane on
+*read* becomes a Tcreate in /pane, del becomes Tremove, cleartag becomes a truncating write to tag, and clean/dirty, scroll/noscroll, mark/nomark and
+addr=dot/dot=addr/limit=addr become their own files. What is left of ctl should be only the verbs with no file analog.
+
+shift-esc stopped leaving raw tty mode on the sdl backend. Commit a624a56 moved raw tty keys to an early-return branch that only knew ctrl-B and bare Esc, so
+shift-esc was forwarded to the child instead. It is the unconditional way out of tty mode and should stay that way.
+
+On tty mode scrolling should work and not always move the focus down to follow a new line. The terminal only moves down to follow new output when the last line
+is already at the bottom, like most terminals and editors. Typing and entering raw mode snap back to live output, so nobody types blind.
+
+The different kinds of layout pardes can initialize (tty mode, file mode, the classic three-shell boot, and the others that already exist) should be an explicit
+enum rather than a chain of ifs over tty_only/shells/file/missing. That part of the code needs to be more explicit. The bare tty startup should always start with
+an empty text pane at the bottom, not focused.
+
+Nested pardes detection stopped working. Spawning a subprocess should export an env variable holding the pardes pid, so a child can see it and call a Look on the
+parent through the 9p mount instead of starting a second session; whether 9p is mounted is another env variable the child can check.
+
+Builtins should call Msg with the builtin name when they are called, minus a few exceptions like Msg itself. This is gated on a verbose config that is on by
+default and can be turned off.
+
+The sr.ht upstream has a macos update pushed to it. Pull it, merge it into the tip here as its own change, then look at what the macos backend gained and port
+those features to the sdl backend wherever it makes sense.
+
+Config options should print symmetrically with the way they are set: instead of showing transparency with a colon and a percent sign it should read like
+`Etcetera 70`, exactly what you would type to set it, and the same for every other setting. LocationsConfig should only open an output window with the current
+config when it is called with no arguments.
+
+Closing the last pane in a column should not delete the column: it should leave a new empty pane there instead. A column closes only when it is closed explicitly,
+so if there is no builtin for that, add a Delcol that sits on the column tagline by default. And in every tagline the builtin that kills or closes the thing should
+come last, which does not look like the case for panes right now.
+
+Pasting regressed on the terminal: inside agent sessions text is being pasted as an image and simply does not work. Reproduce it first, then fix it.
+
+The 9p skill documentation should teach interacting with a running pardes through the /mnt/9p mount with ordinary file tools — cat, echo, ls — as the normal
+ad-hoc path, and fall back to the python client only when nothing is mounted.
+
+Dead sessions are never removed from the posted-9P registry, which is a bug. A session that aborts or is killed leaves both its socket in $XDG_RUNTIME_DIR and its
+symlink under the registry directory, so /mnt/9p/pardes lists entries that give Input/output error on access. postToRegistry only ever replaces its own name's
+entry; nothing sweeps the rest. Posting should sweep the service directory and unlink every entry whose target refuses a connection, and the dangling socket with
+it. cloud9 already classifies a refused connect as stale (post.zig Probe), and 9p_io.zig already has `alive`, which treats uncertainty as live -- that is the right
+bias, so only a definite refusal reaps.
+
+After all of the above, do an optimization pass on startup time for the gui and tty platforms: measure first, then optimize. build.zig already has a `perf` step
+(gesture latency and bounded terminal stress, with --json and a --base baseline to compare against), so a startup measurement belongs there rather than in a new
+harness, and the baseline files are how a regression gets caught later.