Allow semaphore limit queries in the macOS sandbox (#39976)

## Why

Python's `ProcessPoolExecutor` queries `SEM_NSEMS_MAX` through `sysconf`, which reads the `kern.sysv.semmns` sysctl on macOS.

## What changed

- Allow reads of `kern.sysv.semmns` in the base Seatbelt policy.
- Verify `/usr/bin/getconf SEM_NSEMS_MAX` succeeds with both read-only and workspace-write sandbox policies.

GitOrigin-RevId: ab3ae92dc8991729f90a47c1994eedb6c7a2b9cd

codex-rs/sandboxing/src/seatbelt_base_policy.sbpl

@@ -64,6 +64,8 @@
   (sysctl-name "kern.osvariant_status")
   (sysctl-name "kern.osversion")
   (sysctl-name "kern.secure_kernel")
+  ; Python's ProcessPoolExecutor queries this through sysconf(_SC_SEM_NSEMS_MAX).
+  (sysctl-name "kern.sysv.semmns")
   (sysctl-name "kern.usrstack64")
   (sysctl-name "kern.version")
   (sysctl-name "sysctl.proc_cputype")

codex-rs/sandboxing/src/seatbelt_tests.rs

@@ -136,6 +136,41 @@ fn base_policy_allows_node_cpu_sysctls() {
     );
 }
 
+#[test]
+fn seatbelt_allows_semaphore_limit_sysconf() {
+    let workspace = TempDir::new().expect("temp workspace");
+    for policy in [
+        SandboxPolicy::new_read_only_policy(),
+        SandboxPolicy::new_workspace_write_policy(),
+    ] {
+        // getconf calls the same sysconf used by Python's ProcessPoolExecutor.
+        let args = create_seatbelt_command_args_for_legacy_policy(
+            vec!["/usr/bin/getconf".to_string(), "SEM_NSEMS_MAX".to_string()],
+            &policy,
+            workspace.path(),
+            /*enforce_managed_network*/ false,
+            /*network*/ None,
+        )
+        .expect("create seatbelt args");
+        let output = Command::new(MACOS_PATH_TO_SEATBELT_EXECUTABLE)
+            .args(args)
+            .current_dir(workspace.path())
+            .output()
+            .expect("execute semaphore limit query under seatbelt");
+        let stderr = String::from_utf8_lossy(&output.stderr);
+        if !output.status.success()
+            && stderr.contains("sandbox-exec: sandbox_apply: Operation not permitted")
+        {
+            eprintln!("skipping semaphore limit query: nested Seatbelt is unavailable");
+            return;
+        }
+        assert!(
+            output.status.success(),
+            "semaphore limit query should succeed under {policy:?}: {stderr}"
+        );
+    }
+}
+
 #[test]
 fn base_policy_allows_kmp_registration_shm_read_create_and_unlink() {
     let expected = r##"(allow ipc-posix-shm-read-data