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, 14 insertions, 1 deletions

diff --git a/src/builtins.zig b/src/builtins.zig
index 39d70e5d..aa2b2d6d 100644
--- a/src/builtins.zig
+++ b/src/builtins.zig
@@ -137,6 +137,14 @@ pub const registry = struct {
         unreachable;
     }
 
+    /// Does this builtin say its own name on the message row before it runs?
+    /// The ones that own that row themselves declare `quiet` and do not.
+    pub fn announces(b: Builtin()) bool {
+        inline for (manualBuiltinList(), 0..) |T, i|
+            if (@intFromEnum(b) == i) return !(@hasDecl(T, "quiet") and T.quiet);
+        return true; // a setting builtin changes something invisible; say so
+    }
+
     pub fn dispatch(b: Builtin(), c: Ctx) void {
         inline for (manualBuiltinList(), 0..) |T, i|
             if (@intFromEnum(b) == i) return T.run(c);
@@ -259,6 +267,7 @@ pub const Unmount = struct {
 
 pub const Msg = struct {
     pub const takes_arg = true;
+    pub const quiet = true; // it IS the message row
     pub fn run(c: Ctx) void {
         if (c.arg) |text|
             c.p.setMessage(c.id, text)
@@ -542,11 +551,15 @@ pub const LocationsConfig = struct {
     pub const output: OutputTraits = .{ .name = "+LocationsConfig" };
 
     pub fn run(c: Ctx) void {
-        const next = c.p.locations_config.parse(c.arg orelse "") catch |err| {
+        const argument = std.mem.trim(u8, c.arg orelse "", " \t\r\n");
+        const next = c.p.locations_config.parse(argument) catch |err| {
             c.p.reportError(c.id, "LocationsConfig", err);
             return;
         };
         c.p.locations_config = next;
+        // Bare, it is a question, and the window is the answer. With arguments
+        // it is a setting, and a setting that opens a window is noise.
+        if (argument.len != 0) return;
         report(c) catch |err| c.p.reportError(c.id, "LocationsConfig", err);
     }