Fix sandbox multiprocessing test on Python 3.14

codex-rs/exec/tests/suite/sandbox.rs

@@ -77,8 +77,17 @@ async fn python_multiprocessing_lock_works_under_sandbox() {
     };
 
     let python_code = r#"import multiprocessing
+import sys
 from multiprocessing import Lock, Process
 
+# Python 3.14 defaults to forkserver on some Linux distros, which can
+# be blocked by the sandbox. Force fork to keep the test stable.
+if sys.platform.startswith("linux"):
+    try:
+        multiprocessing.set_start_method("fork")
+    except RuntimeError:
+        pass
+
 def f(lock):
     with lock:
         print("Lock acquired in child process")