fix(tests): reduce flakiness in simple mcp server test (#8583)

integration-tests/simple-mcp-server.test.ts

@@ -189,6 +189,25 @@ describe('simple-mcp-server', () => {
       const { chmodSync } = await import('node:fs');
       chmodSync(testServerPath, 0o755);
     }
+
+    // Poll for script for up to 5s
+    const { accessSync, constants } = await import('node:fs');
+    const isReady = await rig.poll(
+      () => {
+        try {
+          accessSync(testServerPath, constants.F_OK);
+          return true;
+        } catch {
+          return false;
+        }
+      },
+      5000, // Max wait 5 seconds
+      100, // Poll every 100ms
+    );
+
+    if (!isReady) {
+      throw new Error('MCP server script was not ready in time.');
+    }
   });
 
   it('should add two numbers', async () => {