diff --git a/tests/integration/app_loader/app_loader_test.ts b/tests/integration/app_loader/app_loader_test.ts
index 7d06a3fd8..6fc556c54 100644
--- a/tests/integration/app_loader/app_loader_test.ts
+++ b/tests/integration/app_loader/app_loader_test.ts
@@ -77,6 +77,8 @@ describe('AgentLoader discovery and loading integration', () => {
   beforeAll(async () => {
     await execAsync('npm install', {cwd: projectPath});
     loader = new AgentLoader(projectPath);
+    // Warm the loader so its one-off bundling cost lands in the hook budget.
+    await loader.preloadAgents();
   });
 
   it(
diff --git a/vitest.config.ts b/vitest.config.ts
index 5ec0393a7..9351c3158 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -29,6 +29,15 @@ const INTEGRATION_HOOK_TIMEOUT_MS = 120000;
  */
 const INTEGRATION_TEST_TIMEOUT_MS = 60000;
 
+/**
+ * Compiled-agent-bundle paths to keep out of Vite's SSR transform in the
+ * `integration` project. AgentLoader esbuilds each agent into a throwaway
+ * multi-MB bundle under `<tmpdir>/adk_agent_loader/<uuid>/`; Vitest inlines it
+ * because it is outside the project root with no `node_modules` segment.
+ * Externalizing drops app_loader_test.ts's transform total from 38.1s to 1.1s.
+ */
+const AGENT_LOADER_BUNDLE_PATTERN = /[\\/]adk_agent_loader[\\/]/;
+
 export default defineConfig({
   test: {
     poolOptions: {
@@ -88,6 +97,7 @@ export default defineConfig({
           environment: 'node',
           hookTimeout: INTEGRATION_HOOK_TIMEOUT_MS,
           testTimeout: INTEGRATION_TEST_TIMEOUT_MS,
+          server: {deps: {external: [AGENT_LOADER_BUNDLE_PATTERN]}},
           alias: {
             '@google/adk': path.resolve(__dirname, './core/src'),
             '@google/adk-integrations': path.resolve(