diff --git a/codex-rs/exec-server/src/fs_sandbox.rs b/codex-rs/exec-server/src/fs_sandbox.rs
index 111d153176..8ef20b2d1d 100644
--- a/codex-rs/exec-server/src/fs_sandbox.rs
+++ b/codex-rs/exec-server/src/fs_sandbox.rs
@@ -230,6 +230,8 @@ fn helper_env_from_vars(
 
 fn helper_env_key_is_allowed(key: &str) -> bool {
     FS_HELPER_ENV_ALLOWLIST.contains(&key)
+        // CoreFoundation consults this before falling back to user lookup during helper startup.
+        || (cfg!(target_os = "macos") && key == "__CF_USER_TEXT_ENCODING")
         || bazel_bwrap_env_key_is_allowed(key)
         || (cfg!(windows) && key.eq_ignore_ascii_case("PATH"))
 }
@@ -434,6 +436,26 @@ mod tests {
         );
     }
 
+    #[cfg(target_os = "macos")]
+    #[test]
+    fn helper_env_preserves_corefoundation_text_encoding() {
+        let env = helper_env_from_vars(
+            [
+                ("__CF_USER_TEXT_ENCODING", "0x1F6:0x0:0x0"),
+                ("HOME", "/Users/test"),
+            ]
+            .map(|(key, value)| (OsString::from(key), OsString::from(value))),
+        );
+
+        assert_eq!(
+            env,
+            HashMap::from([(
+                "__CF_USER_TEXT_ENCODING".to_string(),
+                "0x1F6:0x0:0x0".to_string(),
+            )])
+        );
+    }
+
     #[cfg(windows)]
     #[test]
     fn helper_env_preserves_windows_path_key_for_system_bwrap_discovery() {