Kill signals a command only while it runs, and only the pane it was meant for

A signal effect carried only a slot, so a Kill followed in the same step by
the pane's closing and its slot's reuse signalled the new pane's child; and a
command pane whose child had exited and been reaped kept a process group id
another process could take. The effect now carries the pane's serial, checked
as it is performed, and a host signals no command whose exit it has recorded;
the core already sends Kill only to a command it has not been told is done.

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

1 files changed, 3 insertions, 1 deletions

diff --git a/src/tty/tty.zig b/src/tty/tty.zig
index 8e3809b0..14417cd0 100644
--- a/src/tty/tty.zig
+++ b/src/tty/tty.zig
@@ -1250,7 +1250,9 @@ const Shell = struct {
 
     fn ptySignal(ctx: ?*anyopaque, pane: u8, sig: pardes.PtySignal) void {
         const s = of(ctx);
-        if (s.ptys[pane]) |pt| host_io.signalTty(pt.pid, pt.file.handle, sig);
+        // A command whose exit is recorded is reaped: its group may be
+        // another's by now.
+        if (s.ptys[pane]) |pt| if (!pt.cmd.exited) host_io.signalTty(pt.pid, pt.file.handle, sig);
     }
 
     /// The pane is gone: hang its pty up, which the kernel passes on to the