fix: handle CoreError downcasting properly in error handling

Co-authored-by: aider (openai/andrew/openrouter/qwen/qwen3-coder) <aider@aider.chat>

src/modes/server/api/item.rs

@@ -195,6 +195,12 @@ pub async fn handle_get_item_latest_content(
         }
         Err(CoreError::ItemNotFoundGeneric) => Err(StatusCode::NOT_FOUND),
         Err(e) => {
+            // Check if the error is ItemNotFoundGeneric to return 404
+            if let Some(core_err) = e.downcast_ref::<CoreError>() {
+                if matches!(core_err, CoreError::ItemNotFoundGeneric) {
+                    return Err(StatusCode::NOT_FOUND);
+                }
+            }
             warn!("Failed to find latest item for content: {}", e);
             Err(StatusCode::INTERNAL_SERVER_ERROR)
         }