Add a wrapper around raw response items (#5923)

We currently have nested enums when sending raw response items in the
app-server protocol. This makes downstream schemas confusing because we
need to embed `type`-discriminated enums within each other.

This PR adds a small wrapper around the response item so we can keep the
schemas separate

codex-rs/protocol/src/protocol.rs

@@ -542,12 +542,17 @@ pub enum EventMsg {
     /// Exited review mode with an optional final result to apply.
     ExitedReviewMode(ExitedReviewModeEvent),
 
-    RawResponseItem(ResponseItem),
+    RawResponseItem(RawResponseItemEvent),
 
     ItemStarted(ItemStartedEvent),
     ItemCompleted(ItemCompletedEvent),
 }
 
+#[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema)]
+pub struct RawResponseItemEvent {
+    pub item: ResponseItem,
+}
+
 #[derive(Debug, Clone, Deserialize, Serialize, TS, JsonSchema)]
 pub struct ItemStartedEvent {
     pub thread_id: ConversationId,