Add turn item injection API (#17703)

## Summary
- Add `turn/inject_items` app-server v2 request support for appending
raw Responses API items to a loaded thread history without starting a
turn.
- Generate JSON schema and TypeScript protocol artifacts for the new
params and empty response.
- Document the new endpoint and include a request/response example.
- Preserve compatibility with the typo alias `turn/injet_items` while
returning the canonical method name.

## Testing
- Not run (not requested)

codex-rs/core/src/codex_thread.rs

@@ -199,6 +199,29 @@ impl CodexThread {
         Ok(submission_id)
     }
 
+    /// Append raw Responses API items to the thread's model-visible history.
+    pub async fn inject_response_items(&self, items: Vec<ResponseItem>) -> CodexResult<()> {
+        if items.is_empty() {
+            return Err(CodexErr::InvalidRequest(
+                "items must not be empty".to_string(),
+            ));
+        }
+
+        let turn_context = self.codex.session.new_default_turn().await;
+        if self.codex.session.reference_context_item().await.is_none() {
+            self.codex
+                .session
+                .record_context_updates_and_set_reference_context_item(turn_context.as_ref())
+                .await;
+        }
+        self.codex
+            .session
+            .record_conversation_items(turn_context.as_ref(), &items)
+            .await;
+        self.codex.session.flush_rollout().await?;
+        Ok(())
+    }
+
     pub fn rollout_path(&self) -> Option<PathBuf> {
         self.rollout_path.clone()
     }