fix(playwright): fix flaky tests (#8319)

tests/utils/helpers.ts

@@ -0,0 +1,25 @@
+import fs from 'fs';
+
+/**
+ * Read and JSON-parse a file, retrying until it has parseable content.
+ *
+ * Reading an exported file immediately after the app writes it can observe a
+ * created-but-not-yet-flushed (empty) file — most often on Windows — which makes
+ * JSON.parse throw "Unexpected end of JSON input". Poll until the file has content
+ * that parses as JSON before returning it.
+ */
+export async function readExportedJson(filePath: string, { tries = 50, interval = 100 } = {}) {
+  let lastError: unknown;
+  for (let attempt = 0; attempt < tries; attempt++) {
+    try {
+      const raw = fs.readFileSync(filePath, 'utf8');
+      if (raw.trim().length > 0) {
+        return JSON.parse(raw);
+      }
+    } catch (err) {
+      lastError = err;
+    }
+    await new Promise((resolve) => setTimeout(resolve, interval));
+  }
+  throw lastError ?? new Error(`Timed out waiting for valid JSON at ${filePath}`);
+}