[core] Annotate external goal clear argument

Author: adamvy-oai

codex-rs/app-server/src/request_processors/thread_goal_processor.rs

@@ -227,7 +227,7 @@ impl ThreadGoalRequestProcessor {
             .await
             .map_err(goal_service_error)?;
         if cleared {
-            self.persist_external_thread_goal_if_supported(thread_id, None)
+            self.persist_external_thread_goal_if_supported(thread_id, /*goal*/ None)
                 .await?;
         }