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, 13 insertions, 1 deletions

diff --git a/src/panes.zig b/src/panes.zig
index edd7038f..9a6802d0 100644
--- a/src/panes.zig
+++ b/src/panes.zig
@@ -6273,6 +6273,13 @@ pub const Terminal = struct {
         state.vt.screens.active.scroll(.{ .delta_row = delta });
     }
 
+    /// Is the viewport already showing the last row of output?
+    pub fn atBottom(pane: *const Pane) bool {
+        if (comptime !enabled) return true;
+        const sb = scrollbar(pane);
+        return sb.offset + sb.len >= sb.total;
+    }
+
     /// Snap the viewport back onto live output.
     pub fn followOutput(pane: *Pane) void {
         if (comptime !enabled) return;
@@ -6559,10 +6566,14 @@ pub const Terminal = struct {
         const has_positions = pane.ovl != null or pane.cur_pinned or pane.vsel.active or
             pane.msel.active or pane.nsel > 0 or pane.append_at != null or pane.look_at != null or
             pane.ed_undo_len > 0 or pane.ed_redo_len > 0 or pointerRowCount(pane) > 0;
+        // Sticky bottom, as every other terminal does it: output drags the
+        // viewport down only when the viewport was already on the last row, so
+        // a reader scrolled back into the scrollback stays where they scrolled.
+        const at_bottom = atBottom(pane);
         if (has_positions) ingestWithPositions(pane, bytes) else ingest(pane, bytes);
         p.shell_rows.markStale(pane);
         const body_mode = if (pane.tag_edit) pane.tag_mode else pane.mode;
-        if (body_mode == .tty) followOutput(pane);
+        if (body_mode == .tty and at_bottom) followOutput(pane);
     }
 
     const RowPin = struct { pin: ?*ghostty_vt.Pin = null, offset: i32 = 0 };
@@ -6890,6 +6901,7 @@ pub const Terminal = struct {
         };
 
         pane.mode = .tty;
+        followOutput(pane); // entering raw mode is a request for the live shell
         pane.msel.active = false;
         pane.vsel.active = false;
         pane.nsel = 0;