[codex] Forward turn moderation metadata through app-server (#25710)

## Why
First-party backends can supply turn-scoped moderation metadata that
app-server clients need for client-side presentation. Exposing this as
an experimental typed notification lets opted-in clients consume it
without interpreting raw Responses API events.

## What changed
- forward `response.metadata.openai_chatgpt_moderation_metadata` from
Responses API SSE and WebSocket streams as turn-scoped moderation
metadata
- emit the experimental app-server v2 `turn/moderationMetadata`
notification with `{ threadId, turnId, metadata }`
- add app-server integration coverage for the typed moderation metadata
notification

## Testing
- `just test -p codex-core
build_ws_client_metadata_includes_window_lineage_and_turn_metadata`
- `just test -p codex-core` (fails locally: 46 failures and 1 timeout,
primarily missing `test_stdio_server` and shell snapshot timeouts)
- `just test -p codex-app-server-protocol`
- `just test -p codex-app-server
turn_moderation_metadata_emits_typed_notification_v2`
- `just test -p codex-app-server` (fails locally: 792 passed, 10 failed,
and 5 timed out; failures are in existing environment-sensitive tests,
primarily because nested macOS `sandbox-exec` is not permitted)
- `just write-app-server-schema --experimental --schema-root
/tmp/codex-app-server-schema-experimental`

codex-rs/core/src/session/mod.rs

@@ -359,6 +359,7 @@ use codex_protocol::protocol::ThreadMemoryMode;
 use codex_protocol::protocol::TokenCountEvent;
 use codex_protocol::protocol::TokenUsage;
 use codex_protocol::protocol::TokenUsageInfo;
+use codex_protocol::protocol::TurnModerationMetadataEvent;
 use codex_protocol::protocol::WarningEvent;
 use codex_protocol::user_input::UserInput;
 use codex_tools::ToolEnvironmentMode;
@@ -2637,6 +2638,15 @@ impl Session {
         .await;
     }
 
+    pub(crate) async fn emit_turn_moderation_metadata(
+        self: &Arc<Self>,
+        turn_context: &Arc<TurnContext>,
+        metadata: TurnModerationMetadataEvent,
+    ) {
+        self.send_event(turn_context, EventMsg::TurnModerationMetadata(metadata))
+            .await;
+    }
+
     pub(crate) async fn replace_history(
         &self,
         items: Vec<ResponseItem>,

codex-rs/core/src/session/turn.rs

@@ -1392,6 +1392,7 @@ pub(super) fn realtime_text_for_event(msg: &EventMsg) -> Option<String> {
         | EventMsg::RealtimeConversationClosed(_)
         | EventMsg::ModelReroute(_)
         | EventMsg::ModelVerification(_)
+        | EventMsg::TurnModerationMetadata(_)
         | EventMsg::ContextCompacted(_)
         | EventMsg::ThreadRolledBack(_)
         | EventMsg::TurnStarted(_)
@@ -2057,6 +2058,10 @@ async fn try_run_sampling_request(
                         .await;
                 }
             }
+            ResponseEvent::TurnModerationMetadata(metadata) => {
+                sess.emit_turn_moderation_metadata(&turn_context, metadata)
+                    .await;
+            }
             ResponseEvent::ServerReasoningIncluded(included) => {
                 sess.set_server_reasoning_included(included).await;
             }

codex-rs/core/src/turn_timing.rs

@@ -147,6 +147,7 @@ fn response_event_records_turn_ttft(event: &ResponseEvent) -> bool {
         ResponseEvent::Created
         | ResponseEvent::ServerModel(_)
         | ResponseEvent::ModelVerifications(_)
+        | ResponseEvent::TurnModerationMetadata(_)
         | ResponseEvent::ServerReasoningIncluded(_)
         | ResponseEvent::ToolCallInputDelta { .. }
         | ResponseEvent::Completed { .. }