@@ -14,6 +14,7 @@ import type * as Vite from 'vite' with {
   'resolution-mode': 'import',
 };
 import type { Vitest } from 'vitest/node';
+import { JavaScriptTransformer } from '../../../../tools/javascript-transformer/javascript-transformer';
 import {
   DevServerExternalResultMetadata,
   updateExternalMetadata,
@@ -25,6 +26,11 @@ import {
   type ResultFile,
   ResultKind,
 } from '../../../application/results';
+import {
+  getSupportedBrowsers,
+  isZonelessApp,
+  transformSupportedBrowsersToTargets,
+} from '../../../dev-server/internal';
 import { NormalizedUnitTestBuilderOptions } from '../../options';
 import type { TestExecutor } from '../api';
 import { setupBrowserConfiguration } from './browser-provider';
@@ -57,6 +63,12 @@ export class VitestExecutor implements TestExecutor {
   // Example: `Map<'/path/to/src/app.spec.ts', 'spec-src-app-spec'>`
   private readonly testFileToEntryPoint = new Map<string, string>();
   private readonly entryPointToTestFile = new Map<string, string>();
+  private readonly prebundleTransformer = new JavaScriptTransformer({
+    sourcemap: true,
+    jit: true,
+    thirdPartySourcemaps: false,
+    maxConcurrency: 1,
+  });
 
   constructor(
     projectName: string,
@@ -193,7 +205,7 @@ export class VitestExecutor implements TestExecutor {
     // Vitest does not return a failure result when coverage thresholds are not met.
     // Instead, it sets the process exit code to 1.
     // We check this exit code to determine if the test run should be considered a failure.
-    if (success && process.exitCode === 1) {
+    if (success && this.options.coverage?.enabled && process.exitCode === 1) {
       success = false;
       finalResultReason = 'Test run failed due to unmet coverage thresholds.';
       // Reset the exit code to prevent it from carrying over to subsequent runs/builds
@@ -218,17 +230,20 @@ export class VitestExecutor implements TestExecutor {
     const timeoutMs = 10_000;
 
     try {
-      await Promise.race([
-        this.vitest.close(),
-        setTimeout(timeoutMs, undefined, { signal: controller.signal, ref: false })
-          .then(() => {
-            this.logger.warn(
-              `Vitest instance failed to close cleanly within ${timeoutMs}ms. Continuing teardown...`,
-            );
-          })
-          .catch(() => {
-            // Suppress AbortError triggered by controller.abort() when close() resolves first
-          }),
+      await Promise.all([
+        this.prebundleTransformer.close(),
+        Promise.race([
+          this.vitest.close(),
+          setTimeout(timeoutMs, undefined, { signal: controller.signal, ref: false })
+            .then(() => {
+              this.logger.warn(
+                `Vitest instance failed to close cleanly within ${timeoutMs}ms. Continuing teardown...`,
+              );
+            })
+            .catch(() => {
+              // Suppress AbortError triggered by controller.abort() when close() resolves first
+            }),
+        ]),
       ]);
     } catch (error: unknown) {
       assertIsError(error);
@@ -334,6 +349,7 @@ export class VitestExecutor implements TestExecutor {
       buildResultFiles: this.buildResultFiles,
       testFileToEntryPoint: this.testFileToEntryPoint,
       setupFiles: testSetupFiles,
+      prebundleTransformer: this.prebundleTransformer,
     });
 
     const debugOptions = debug
@@ -379,6 +395,13 @@ export class VitestExecutor implements TestExecutor {
     });
     this.debugLog(DebugLogLevel.Verbose, 'Included test files (after filtering):', include);
 
+    const supportedBrowsers = getSupportedBrowsers(projectRoot, this.logger);
+    const target = transformSupportedBrowsersToTargets(supportedBrowsers);
+    if (!isZonelessApp(this.options.polyfills)) {
+      // Rolldown doesn't have an option to support Zone.js/async-await, so we need to support es2016.
+      target.push('es2016');
+    }
+
     const vitestConfig = {
       config: externalConfigPath,
       root: workspaceRoot,
@@ -412,6 +435,8 @@ export class VitestExecutor implements TestExecutor {
           watch,
           isolate: this.options.isolate,
           preserveSymlinks: this.options.preserveSymlinks,
+          prebundleTransformer: this.prebundleTransformer,
+          target,
         }),
       ],
     };
 
@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.dev/license
  */
 
+import { needsLinking } from '@angular/compiler-cli/linker';
 import assert from 'node:assert';
 import { readFile } from 'node:fs/promises';
 import { platform } from 'node:os';
@@ -18,7 +19,9 @@ import type {
   Vite,
   VitestPluginContext,
 } from 'vitest/node';
+import type { JavaScriptTransformer } from '../../../../tools/javascript-transformer/javascript-transformer';
 import { createBuildAssetsMiddleware } from '../../../../tools/vite/middlewares/assets-middleware';
+import { getDepOptimizationConfig } from '../../../../tools/vite/utils';
 import { toPosixPath } from '../../../../utils/path';
 import { createProjectResolver } from '../../../../utils/resolve-project';
 import type { ResultFile } from '../../../application/results';
@@ -37,6 +40,7 @@ interface PluginOptions {
   projectName: string;
   buildResultFiles: ReadonlyMap<string, ResultFile>;
   testFileToEntryPoint: ReadonlyMap<string, string>;
+  prebundleTransformer: JavaScriptTransformer;
   setupFiles: readonly string[];
 }
 
@@ -55,6 +59,8 @@ interface VitestConfigPluginOptions {
   watch: boolean;
   isolate: boolean | undefined;
   preserveSymlinks?: boolean;
+  prebundleTransformer: JavaScriptTransformer;
+  target: string[];
 }
 
 async function findTestEnvironment(
@@ -253,11 +259,21 @@ export async function createVitestConfigPlugin(
           // Default to `false` to align with the Karma/Jasmine experience.
           isolate: false,
           sequence: { setupFiles: 'list' },
+          server: {
+            deps: {
+              inline: options.optimizeDepsInclude.filter((dep) => !dep.startsWith('@angular/')),
+            },
+          },
         },
-        optimizeDeps: {
-          noDiscovery: true,
+        optimizeDeps: getDepOptimizationConfig({
+          target: options.target,
+          disabled: false,
+          exclude: [],
           include: options.optimizeDepsInclude,
-        },
+          prebundleTransformer: options.prebundleTransformer,
+          thirdPartySourcemaps: false,
+          define: undefined,
+        }),
         resolve: {
           mainFields: ['es2020', 'module', 'main'],
           conditions: ['es2015', 'es2020', 'module', ...(browser ? ['browser'] : [])],
@@ -314,7 +330,13 @@ async function loadResultFile(file: ResultFile): Promise<string> {
 }
 
 export function createVitestPlugins(pluginOptions: PluginOptions): Vite.Plugin[] {
-  const { workspaceRoot, buildResultFiles, testFileToEntryPoint, setupFiles } = pluginOptions;
+  const {
+    workspaceRoot,
+    buildResultFiles,
+    testFileToEntryPoint,
+    setupFiles,
+    prebundleTransformer,
+  } = pluginOptions;
   const isWindows = platform() === 'win32';
   const setupFileSet = new Set(
     setupFiles.map((file) =>
@@ -324,6 +346,19 @@ export function createVitestPlugins(pluginOptions: PluginOptions): Vite.Plugin[]
   let vitestConfig: ResolvedConfig;
 
   return [
+    {
+      name: 'angular:linker',
+      enforce: 'pre',
+      async transform(code: string, id: string) {
+        if (!needsLinking(id, code)) {
+          return null;
+        }
+
+        const transformedData = await prebundleTransformer.transformData(id, code);
+
+        return Buffer.from(transformedData).toString('utf-8');
+      },
+    },
     {
       name: 'angular:test-in-memory-provider',
       enforce: 'pre',
 
@@ -0,0 +1,89 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+import { execute } from '../../index';
+import {
+  BASE_OPTIONS,
+  describeBuilder,
+  UNIT_TEST_BUILDER_INFO,
+  setupApplicationTarget,
+} from '../setup';
+
+describeBuilder(execute, UNIT_TEST_BUILDER_INFO, (harness) => {
+  describe('Behavior: "Vitest Angular Linker"', () => {
+    it('should link partially-compiled packages with cross-class references', async () => {
+      setupApplicationTarget(harness);
+
+      harness.useTarget('test', {
+        ...BASE_OPTIONS,
+      });
+
+      await harness.writeFile(
+        'node_modules/test-lib/package.json',
+        JSON.stringify({
+          name: 'test-lib',
+          version: '1.0.0',
+          type: 'module',
+          main: './fesm2022/test-lib.mjs',
+          types: './index.d.ts',
+          exports: {
+            '.': {
+              types: './index.d.ts',
+              default: './fesm2022/test-lib.mjs',
+            },
+          },
+        }),
+      );
+
+      await harness.writeFile(
+        'node_modules/test-lib/index.d.ts',
+        `
+        export declare class CascadeSelectSub {}
+        export declare class CascadeSelect {}
+        `,
+      );
+
+      await harness.writeFile(
+        'node_modules/test-lib/fesm2022/test-lib.mjs',
+        `
+        import * as i0 from "@angular/core";
+        export class CascadeSelectSub {
+          static ɵfac = i0.ɵɵngDeclareFactory({
+            minVersion: "12.0.0",
+            version: "14.0.0",
+            ngImport: i0,
+            type: CascadeSelectSub,
+            deps: [{ token: CascadeSelect }],
+            target: i0.ɵɵFactoryTarget.Component
+          });
+        }
+        export class CascadeSelect {}
+        `,
+      );
+
+      await harness.writeFile(
+        'src/app/app.component.spec.ts',
+        `
+        import { describe, it, expect } from 'vitest';
+        import { CascadeSelectSub, CascadeSelect } from 'test-lib';
+
+        describe('CascadeSelect test', () => {
+          it('loads without ReferenceError', () => {
+            expect(CascadeSelectSub).toBeDefined();
+            expect(CascadeSelect).toBeDefined();
+          });
+        });
+        `,
+      );
+
+      const { result } = await harness.executeOnce();
+
+      expect(result?.success).toBeTrue();
+    });
+  });
+});