test: fix pane shell idle foreground-command race (#4691)

The interactive-shell idle test sent SIGINT as soon as it observed the
shell was busy. That condition can be true before the shell finishes
moving the command into its own foreground process group, so the
interrupt could arrive before the command reset its signal dispositions.
The command then survived in a stale foreground group while the shell
showed a prompt, and the pane was never observed idle again.

Run cat and end it with EOF instead. cat blocks on stdin, so the busy
state is stable, and EOF avoids the interrupt/job-control race.

1 files changed, 8 insertions, 2 deletions

diff --git a/src/detect/mod.rs b/src/detect/mod.rs
index 7d7759d2..146c3089 100644
--- a/src/detect/mod.rs
+++ b/src/detect/mod.rs
@@ -1962,9 +1962,15 @@ mod tests {
         let mut writer = pair.master.take_writer().expect("no writer");
 
         assert!(wait_for(true, pid), "interactive shell should start idle");
-        writer.write_all(b"sleep 999\n").unwrap();
+        // End the foreground command with EOF rather than SIGINT. An interrupt
+        // sent while the shell is still moving the command into its own
+        // foreground process group can be delivered before the command resets
+        // its signal dispositions, leaving it running in a stale foreground
+        // group while the shell shows a prompt. `cat` blocks until stdin hits
+        // EOF, so it stays reliably busy until we end it.
+        writer.write_all(b"cat\n").unwrap();
         assert!(wait_for(false, pid), "shell running a command is not idle");
-        writer.write_all(&[3]).unwrap();
+        writer.write_all(&[4]).unwrap();
         assert!(
             wait_for(true, pid),
             "shell should be idle after the command ends"