Add warning on compact (#6052)

This PR introduces the ability for `core` to send `warnings` as it can
send `errors. It also sends a warning on compaction.

<img width="811" height="187" alt="image"
src="https://github.com/user-attachments/assets/0947a42d-b720-420d-b7fd-115f8a65a46a"
/>

codex-rs/mcp-server/src/codex_tool_runner.rs

@@ -204,6 +204,9 @@ async fn run_codex_tool_session_inner(
                         outgoing.send_response(request_id.clone(), result).await;
                         break;
                     }
+                    EventMsg::Warning(_) => {
+                        continue;
+                    }
                     EventMsg::ApplyPatchApprovalRequest(ApplyPatchApprovalRequestEvent {
                         call_id,
                         reason,