fix(@angular/build): ensure @angular/compiler is loaded for Vitest TestBed initialization

Explicitly import '@angular/compiler' at the top of the Vitest TestBed initialization virtual file. This ensures the compiler facade is published before any modules or providers (such as those configured via 'providersFile') are evaluated, avoiding JIT compilation errors when injectable dependencies are resolved during test initialization.

Author: clydin

packages/angular/build/src/builders/unit-test/runners/vitest/build-options.ts

@@ -47,6 +47,7 @@ function createTestBedInitVirtualFile(
   // when running Vitest in non-isolated mode with JSDOM. It looks up the
   // document dynamically on every operation instead of caching it.
   return `
+    import '@angular/compiler';
     ${hasLocalize ? "import '@angular/localize/init';" : ''}
     // Initialize the Angular testing environment
     import { NgModule, provideZoneChangeDetection } from '@angular/core';

packages/angular/build/src/builders/unit-test/tests/options/providers-file_spec.ts

@@ -60,5 +60,59 @@ describeBuilder(execute, UNIT_TEST_BUILDER_INFO, (harness) => {
       const { result } = await harness.executeOnce();
       expect(result?.success).toBeTrue();
     });
+
+    it('should work with providers that inject services requiring JIT compilation', async () => {
+      await harness.writeFiles({
+        'src/test.service.ts': `
+          import { Injectable, inject } from '@angular/core';
+          import { Router } from '@angular/router';
+
+          @Injectable({ providedIn: 'root' })
+          export class TestService {
+            router = inject(Router);
+          }
+        `,
+        'src/test.providers.ts': `
+          import { TestService } from './test.service';
+          export default [TestService];
+        `,
+        'src/app/app.component.spec.ts': `
+          import { TestBed } from '@angular/core/testing';
+          import { AppComponent } from './app.component';
+          import { TestService } from '../test.service';
+          import { describe, expect, it } from 'vitest';
+
+          describe('AppComponent', () => {
+            it('should create the app and inject TestService', () => {
+              TestBed.configureTestingModule({
+                declarations: [AppComponent],
+              });
+              const fixture = TestBed.createComponent(AppComponent);
+              const app = fixture.componentInstance;
+              const testService = TestBed.inject(TestService);
+              expect(app).toBeTruthy();
+              expect(testService).toBeTruthy();
+              expect(testService.router).toBeTruthy();
+            });
+          });
+        `,
+      });
+
+      await harness.modifyFile('src/tsconfig.spec.json', (content) => {
+        const tsConfig = JSON.parse(content);
+        tsConfig.files ??= [];
+        tsConfig.files.push('test.service.ts', 'test.providers.ts');
+
+        return JSON.stringify(tsConfig);
+      });
+
+      harness.useTarget('test', {
+        ...BASE_OPTIONS,
+        providersFile: 'src/test.providers.ts',
+      });
+
+      const { result } = await harness.executeOnce();
+      expect(result?.success).toBeTrue();
+    });
   });
 });