Run a line at a terminal's prompt through pty/run and read how it ended

/pane/<n>/pty/run takes factotum's rpc shape: write one line on an open,
read the answer on that same open. The answer is exit N once the command
ended and the shell is back at a prompt; busy at once when a command runs,
text is typed at the prompt, or the shell has not drawn its first prompt;
error not run when the shell refused the line without running it (fish on
a syntax error keeps it on the prompt, so it is taken back with Ctrl-U);
error shell gone when the pane closes or its shell is replaced; error no
prompt marks for a shell pardes could not instrument.

The end comes from the shell's OSC 133 marks. ghostty parses D's exit
status and drops it, so the stream now runs through a handler that wraps
ghostty's and follows prompt -> input -> running -> done. The marks pardes
injects into bash and fish carry aid=pardes and only those count, so fish
4's own marks (which doubled ours), a nested shell's, and a stray 133;D in
printed output are ignored.

Checked end to end against real bash and fish: false, exit 7, a syntax
error, sleep, busy while running, and the pane closing mid-command.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

1 files changed, 6 insertions, 4 deletions

diff --git a/src/ninep/events.zig b/src/ninep/events.zig
index ebd1cd2c..fa0a4975 100644
--- a/src/ninep/events.zig
+++ b/src/ninep/events.zig
@@ -128,6 +128,7 @@ pub fn noteInstall(p: *Pardes, id: usize) void {
 /// A pane leaving; one never announced leaves silently.
 pub fn noteRetire(p: *Pardes, id: usize, pane: *Pane) void {
     if (id >= MAX_PANES) return;
+    tree.pty.shellGone(p, id);
     if (p.fs.panes[id].unannounced) {
         p.fs.panes[id].unannounced = false;
         return;
@@ -168,10 +169,11 @@ fn pushLog(p: *Pardes, record: []u8) void {
         c.* = ' ';
     };
     // One record larger than the ring would push every other out and then
-    // not fit itself; cut it to what fits instead.
-    const fit = @min(record.len, p.fs.log.cap - 4);
-    record[fit - 1] = '\n';
-    p.fs.log.push(p.gpa, record[0..fit]);
+    // not fit itself; cut it to what fits instead, on a character boundary.
+    var end = @min(record.len, p.fs.log.cap - 4) - 1;
+    while (end > 0 and record[end] & 0xC0 == 0x80) end -= 1;
+    record[end] = '\n';
+    p.fs.log.push(p.gpa, record[0 .. end + 1]);
 }
 
 /// An open freezes the ring's text, so `cat log` answers what happened lately