Include sandbox mode in response metadata (#37507)

## What changed

- Add the effective permission profile as `sandbox_mode` in turn metadata for regular, prewarm, compaction, and detached memory requests.
- Reserve `sandbox_mode` so client-provided metadata cannot override the computed value.

## Testing

- Cover metadata headers and request bodies for read-only and danger-full-access modes.

GitOrigin-RevId: 13c690cc99bc2691023f281ca527af049bb1286f

codex-rs/memories/write/src/runtime.rs

@@ -266,6 +266,7 @@ impl MemoryStartupContext {
 
         let mut client_session = model_client.new_session();
         let window_id = format!("{}:0", self.thread_id);
+        let permission_profile = config.permissions.effective_permission_profile();
         let responses_metadata = detached_memory_responses_metadata(
             installation_id,
             session_id_string,
@@ -273,6 +274,7 @@ impl MemoryStartupContext {
             window_id,
             &session_source,
             &config.cwd,
+            &permission_profile,
             /*sandbox*/ None,
         )
         .await;