diff --git a/core/test/sessions/vertex_ai_session_service_test.ts b/core/test/sessions/vertex_ai_session_service_test.ts
index 4a15053c4..2a6afc43f 100644
--- a/core/test/sessions/vertex_ai_session_service_test.ts
+++ b/core/test/sessions/vertex_ai_session_service_test.ts
@@ -5,8 +5,8 @@
  */
 
 import {Sessions} from '@google-cloud/vertexai/build/src/genai/sessions.js';
+import type {Session} from '@google/adk';
 import {createEvent, State, VertexAiSessionService} from '@google/adk';
-import {Session} from '@google/adk/sessions/session.js';
 import {ApiError} from '@google/genai';
 import {beforeEach, describe, expect, it, vi} from 'vitest';
 
@@ -24,8 +24,8 @@ vi.mock('nodejs-vertexai', () => ({
 import {
   isVertexAiConnectionString,
   quoteFilterLiteral,
-} from '@google/adk/sessions/vertex_ai_session_service.js';
-import {logger} from '@google/adk/utils/logger.js';
+} from '../../src/sessions/vertex_ai_session_service.js';
+import {logger} from '../../src/utils/logger.js';
 
 describe('isVertexAiConnectionString', () => {
   it('returns true for vertexai://', () => {
diff --git a/tests/integration/agents/agent_with_sandbox_executor_test.ts b/tests/integration/agents/agent_with_sandbox_executor_test.ts
index 17f952ba0..539e8b75c 100644
--- a/tests/integration/agents/agent_with_sandbox_executor_test.ts
+++ b/tests/integration/agents/agent_with_sandbox_executor_test.ts
@@ -6,9 +6,9 @@
 
 import {Client} from '@google-cloud/vertexai';
 import {AgentEngineSandboxCodeExecutor, LlmAgent} from '@google/adk';
-import {responseProcessor} from '@google/adk/agents/processors/code_execution_request_processor.js';
 import {FinishReason} from '@google/genai';
 import {describe, expect, it, vi} from 'vitest';
+import {responseProcessor} from '../../../core/src/agents/processors/code_execution_request_processor.js';
 import {
   createRunner,
   GeminiWithMockResponses,
diff --git a/tests/integration/vitest_alias_test.ts b/tests/integration/vitest_alias_test.ts
new file mode 100644
index 000000000..ba763f717
--- /dev/null
+++ b/tests/integration/vitest_alias_test.ts
@@ -0,0 +1,57 @@
+/**
+ * @license
+ * Copyright 2026 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import path from 'node:path';
+import {fileURLToPath} from 'node:url';
+import {describe, expect, it} from 'vitest';
+import {workspaceAliases} from '../../vitest.config.js';
+
+const REPO_ROOT = path.resolve(
+  path.dirname(fileURLToPath(import.meta.url)),
+  '../..',
+);
+
+/**
+ * Applies the alias entries the way `@rollup/plugin-alias` does for a `RegExp`
+ * `find`, so a silent revert to the prefix-matching string form matches nothing
+ * and fails these tests.
+ */
+function matchingAliases(specifier: string) {
+  return workspaceAliases.filter(
+    (entry) => entry.find instanceof RegExp && entry.find.test(specifier),
+  );
+}
+
+describe('workspaceAliases', () => {
+  it('matches only the bare package specifiers', () => {
+    expect(matchingAliases('@google/adk')).toHaveLength(1);
+    expect(matchingAliases('@google/adk-integrations')).toHaveLength(1);
+
+    for (const deepSpecifier of [
+      '@google/adk/sessions/session.js',
+      '@google/adk/agents/processors/code_execution_request_processor.js',
+      '@google/adk-integrations/foo.js',
+      '@google/adk-devtools',
+    ]) {
+      expect(matchingAliases(deepSpecifier)).toEqual([]);
+    }
+  });
+
+  it('resolves each package to its source root', () => {
+    expect(matchingAliases('@google/adk')).toEqual([
+      {
+        find: expect.any(RegExp),
+        replacement: path.resolve(REPO_ROOT, 'core/src'),
+      },
+    ]);
+    expect(matchingAliases('@google/adk-integrations')).toEqual([
+      {
+        find: expect.any(RegExp),
+        replacement: path.resolve(REPO_ROOT, 'integrations/src'),
+      },
+    ]);
+  });
+});
diff --git a/vitest.config.ts b/vitest.config.ts
index 1b7eaee63..c4bfba0ec 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -20,6 +20,28 @@ const INTEGRATION_HOOK_TIMEOUT_MS = 120000;
  */
 const INTEGRATION_TEST_TIMEOUT_MS = 60000;
 
+/**
+ * Maps the workspace package names onto their source trees, shared by every
+ * test project.
+ *
+ * The patterns are anchored regexes rather than plain strings: a string `find`
+ * matches the package root *and every subpath under it*, so `'@google/adk'`
+ * also rewrote `@google/adk/sessions/session.js` to
+ * `core/src/sessions/session.js`. `core/package.json` and
+ * `integrations/package.json` export only `"."`, so that subpath resolves for
+ * nobody outside vitest: the alias made the harness accept imports that `tsc`
+ * (`moduleResolution: nodenext`) and Node both reject.
+ *
+ * Import an internal symbol through a relative `../src/...` path instead.
+ */
+export const workspaceAliases = [
+  {find: /^@google\/adk$/, replacement: path.resolve(__dirname, './core/src')},
+  {
+    find: /^@google\/adk-integrations$/,
+    replacement: path.resolve(__dirname, './integrations/src'),
+  },
+];
+
 export default defineConfig({
   test: {
     poolOptions: {
@@ -35,13 +57,7 @@ export default defineConfig({
         test: {
           name: 'unit:core',
           environment: 'node',
-          alias: {
-            '@google/adk': path.resolve(__dirname, './core/src'),
-            '@google/adk-integrations': path.resolve(
-              __dirname,
-              './integrations/src',
-            ),
-          },
+          alias: workspaceAliases,
           include: ['core/test/**/*_test.ts'],
         },
       },
@@ -49,13 +65,7 @@ export default defineConfig({
         test: {
           name: 'unit:dev',
           environment: 'node',
-          alias: {
-            '@google/adk': path.resolve(__dirname, './core/src'),
-            '@google/adk-integrations': path.resolve(
-              __dirname,
-              './integrations/src',
-            ),
-          },
+          alias: workspaceAliases,
           include: ['dev/test/**/*_test.ts'],
         },
       },
@@ -63,13 +73,7 @@ export default defineConfig({
         test: {
           name: 'unit:integrations',
           environment: 'node',
-          alias: {
-            '@google/adk': path.resolve(__dirname, './core/src'),
-            '@google/adk-integrations': path.resolve(
-              __dirname,
-              './integrations/src',
-            ),
-          },
+          alias: workspaceAliases,
           include: ['integrations/test/**/*_test.ts'],
         },
       },
@@ -79,13 +83,7 @@ export default defineConfig({
           environment: 'node',
           hookTimeout: INTEGRATION_HOOK_TIMEOUT_MS,
           testTimeout: INTEGRATION_TEST_TIMEOUT_MS,
-          alias: {
-            '@google/adk': path.resolve(__dirname, './core/src'),
-            '@google/adk-integrations': path.resolve(
-              __dirname,
-              './integrations/src',
-            ),
-          },
+          alias: workspaceAliases,
           include: ['tests/integration/**/*_test.ts'],
         },
       },
@@ -93,13 +91,7 @@ export default defineConfig({
         test: {
           name: 'e2e',
           environment: 'node',
-          alias: {
-            '@google/adk': path.resolve(__dirname, './core/src'),
-            '@google/adk-integrations': path.resolve(
-              __dirname,
-              './integrations/src',
-            ),
-          },
+          alias: workspaceAliases,
           include: ['tests/e2e/**/*_test.ts'],
         },
       },
@@ -107,13 +99,7 @@ export default defineConfig({
         test: {
           name: 'cross-language',
           environment: 'node',
-          alias: {
-            '@google/adk': path.resolve(__dirname, './core/src'),
-            '@google/adk-integrations': path.resolve(
-              __dirname,
-              './integrations/src',
-            ),
-          },
+          alias: workspaceAliases,
           include: ['tests/cross_language/**/*_test.ts'],
         },
       },