test(examples-chat): pin no-nav-loop invariant

examples/chat/angular/src/app/shell/demo-shell.component.spec.ts

@@ -1,7 +1,7 @@
 import { signal } from '@angular/core';
 import { describe, it, expect, beforeEach } from 'vitest';
 import { TestBed } from '@angular/core/testing';
-import { provideRouter, Router } from '@angular/router';
+import { provideRouter, Router, NavigationEnd } from '@angular/router';
 import { LangGraphThreadsAdapter } from '@ngaf/langgraph';
 import { DemoShell } from './demo-shell.component';
 
@@ -215,6 +215,38 @@ describe('DemoShell — URL thread sync', () => {
     };
     expect(cmp.threadIdSignal()).toBe('url-thread');
   });
+
+  it('does not re-navigate when hydrating from URL (no nav-loop)', async () => {
+    // Regression guard for the URL↔signal sync invariant that every PR
+    // in the routing chain (#500/#504/#514/#518/#527) was dancing
+    // around: when the URL→signal effect hydrates `threadIdSignal`
+    // from `/embed/<id>`, the subsequent signal→URL effect must see
+    // signal === urlId and short-circuit (compare-and-set guard).
+    // Without that guard we'd loop: URL → signal → router.navigate →
+    // URL again, observable as extra NavigationEnd events.
+    const router = TestBed.inject(Router);
+    await router.navigateByUrl('/embed/no-loop-thread');
+
+    // Subscribe BEFORE createComponent so we capture any NavigationEnd
+    // events the component's effects might emit. The initial nav above
+    // already fired before we subscribed, so it doesn't count.
+    const navEnds: string[] = [];
+    const sub = router.events.subscribe((e) => {
+      if (e instanceof NavigationEnd) navEnds.push(e.urlAfterRedirects);
+    });
+
+    const fx = TestBed.createComponent(DemoShell);
+    fx.detectChanges();
+    sub.unsubscribe();
+
+    const cmp = fx.componentInstance as unknown as {
+      threadIdSignal: { (): string | null };
+    };
+    expect(cmp.threadIdSignal()).toBe('no-loop-thread');
+    // Zero NavigationEnd events — the signal→URL effect short-circuited
+    // because signal already matched urlState (compare-and-set guard).
+    expect(navEnds).toEqual([]);
+  });
 });
 
 describe('DemoShell — URL knob hydration', () => {