fix: clean up MCP subprocesses after abrupt parent exit (#8242)

Signed-off-by: fre <anonwurcod@proton.me>
Signed-off-by: Douwe Osinga <douwe@squareup.com>
Co-authored-by: Oz <oz-agent@warp.dev>
Co-authored-by: Douwe Osinga <douwe@squareup.com>

crates/goose/src/subprocess.rs

@@ -3,6 +3,25 @@ use tokio::process::Command;
 #[cfg(windows)]
 const CREATE_NO_WINDOW_FLAG: u32 = 0x08000000;
 
+#[cfg(target_os = "linux")]
+fn configure_parent_death_signal(command: &mut Command) {
+    let parent_pid = unsafe { libc::getpid() };
+
+    unsafe {
+        command.pre_exec(move || {
+            if libc::prctl(libc::PR_SET_PDEATHSIG, libc::SIGTERM) != 0 {
+                return Err(std::io::Error::last_os_error());
+            }
+
+            if libc::getppid() != parent_pid {
+                return Err(std::io::Error::from_raw_os_error(libc::ESRCH));
+            }
+
+            Ok(())
+        });
+    }
+}
+
 pub trait SubprocessExt {
     fn set_no_window(&mut self) -> &mut Self;
 }
@@ -34,5 +53,7 @@ pub fn configure_subprocess(command: &mut Command) {
     // SIGINT when the user presses Ctrl+C in the terminal.
     #[cfg(unix)]
     command.process_group(0);
+    #[cfg(target_os = "linux")]
+    configure_parent_death_signal(command);
     command.set_no_window();
 }