webui: make diff loading error message more useful
diff --git a/webui/src/web-components/git-data-service.ts b/webui/src/web-components/git-data-service.ts
index 69d108d..b3aec25 100644
--- a/webui/src/web-components/git-data-service.ts
+++ b/webui/src/web-components/git-data-service.ts
@@ -161,8 +161,9 @@
       const response = await fetch(url);
 
       if (!response.ok) {
+        const errorText = await response.text();
         throw new Error(
-          `Failed to fetch working copy content: ${response.statusText}`,
+          `Failed to fetch working copy content (${response.status}): ${errorText}`,
         );
       }