test(platform-server): fix race condition in incremental hydration test

The test was using a brittle fixed timeout of 10ms to wait for change detection to run in Zoneless mode. This failed in CI sometimes presumably because CI can execute slower based on resource constraints. This commit replaces it with a polling approach which checks until the expected content is rendered.

Author: dgp1130

packages/platform-server/test/incremental_hydration_spec.ts

@@ -29,6 +29,7 @@ import {
 } from '@angular/core';
 
 import {
+  DOCUMENT,
   isPlatformServer,
   Location,
   ɵPLATFORM_BROWSER_ID as PLATFORM_BROWSER_ID,
@@ -2131,6 +2132,12 @@ describe('platform-server partial hydration integration', () => {
   });
 
   describe('control flow', () => {
+    let pollingInterval: ReturnType<typeof setInterval>;
+
+    afterEach(() => {
+      if (pollingInterval !== undefined) clearInterval(pollingInterval);
+    });
+
     it('should support hydration for all items in a for loop', async () => {
       @Component({
         selector: 'app',
@@ -2164,13 +2171,31 @@ describe('platform-server partial hydration integration', () => {
           this.value.set('end');
         }
         registry = inject(DEHYDRATED_BLOCK_REGISTRY);
+        private readonly doc = inject(DOCUMENT);
 
         constructor() {
           // TODO: Understand why this is needed to get the full rendering of the HTML
           // Without it, bindings aren't properly rendered in SSR and the test fails.
           // There was no issue with the zone based scheduler.
-          const remove = inject(PendingTasks).add();
-          setTimeout(() => remove(), 10);
+          const pendingTasks = inject(PendingTasks);
+          pendingTasks.run(
+            () =>
+              new Promise<void>((resolve) => {
+                pollingInterval = setInterval(() => {
+                  const el = this.doc.getElementById('item-1');
+                  if (el && el.textContent?.includes('defer block 1 rendered')) {
+                    clearInterval(pollingInterval);
+                    resolve();
+                  }
+                }, 10);
+
+                // Fallback timeout to prevent indefinite hanging
+                setTimeout(() => {
+                  clearInterval(pollingInterval);
+                  resolve();
+                }, 1000);
+              }),
+          );
         }
       }