Create updating page

packages/builder/src/api.js

@@ -46,8 +46,12 @@ export const API = createAPIClient({
     }
   },
   onMigrationDetected: appId => {
-    window.location = `/builder/updating/${appId}?returnUrl=${encodeURI(
-      window.location
-    )}`
+    const updatingUrl = `/builder/updating/${appId}`
+
+    if (window.location.pathname === updatingUrl) {
+      return
+    }
+
+    window.location = `${updatingUrl}?returnUrl=${encodeURI(window.location)}`
   },
 })

packages/builder/src/pages/builder/updating/[appId].svelte

@@ -0,0 +1,14 @@
+<script>
+  import Spinner from "components/common/Spinner.svelte"
+</script>
+
+<div class="loading">
+  <Spinner size="20" />
+</div>
+
+<style>
+  .loading {
+    display: flex;
+    justify-content: center;
+  }
+</style>