fix: accept both -1 and 143 exit codes in timeout test

On GHA runners, the sleep process may receive SIGTERM from the runner's
process management before our 1-second timeout fires. Both exit codes
are valid: -1 (our timeout sentinel) and 143 (128 + SIGTERM from
external signal). exec sleep prevents orphan processes.

Author: richiemcilroy

crates/sandchest-agent/src/exec.rs

@@ -438,8 +438,12 @@ mod tests {
             })
             .expect("should have exit event");
 
-        // Timed-out process exits with -1 (our sentinel)
-        assert_eq!(exit_event.exit_code, -1);
+        // Timed-out process exits with -1 (our sentinel) or 143 (128 + SIGTERM)
+        assert!(
+            exit_event.exit_code == -1 || exit_event.exit_code == 143,
+            "expected exit code -1 or 143, got {}",
+            exit_event.exit_code
+        );
     }
 
     #[tokio::test]