new error state, tests to cover

__tests__/saveCache.test.ts

@@ -237,7 +237,8 @@ test('save with server error should fail', async () => {
     .mockReturnValue(
       Promise.resolve({
         ok: true,
-        signedUploadUrl: 'https://blob-storage.local?signed=true'
+        signedUploadUrl: 'https://blob-storage.local?signed=true',
+        message: ""
       })
     )