pty/ctl exec fails the write when the shell cannot start; a directory removed under a shell leaves its name

`exec` on pty/ctl restarted a shell in a directory that was gone, the
write succeeding and the pane dead; and the pane was then renamed
`<dir> (deleted)` from /proc, so a restart failed even once the directory
was back. `exec` is now refused up front, ENOENT, where the directory is
gone; a shell the host cannot start fails the waiting write (late
failure, as a Save's); and a `(deleted)` cwd is no name to take.

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

1 files changed, 6 insertions, 0 deletions

diff --git a/src/pardes.zig b/src/pardes.zig
index 60a5dfe3..1afb1e24 100644
--- a/src/pardes.zig
+++ b/src/pardes.zig
@@ -5251,6 +5251,12 @@ pub const Pardes = struct {
             p.reportFailure(id, "shell: directory missing (no such directory)")
         else
             p.reportError(id, "shell", err);
+        // A 9P write that asked for the shell (pty/ctl's exec), waiting on
+        // it, fails with what was said, as a failed Save's does.
+        const said = pane.msg[0..pane.msg_len];
+        const kept = @import("Messages.zig").clip(said, p.fs.late_failure.len);
+        @memcpy(p.fs.late_failure[0..kept.len], kept);
+        p.fs.late_failure_len = @intCast(kept.len);
         // A command that never started ended: `exit 127`, as a shell says of
         // a command it could not run, so a follower waiting on its exit
         // hears one, its tag stops saying it runs, and Kill finds nothing.