fix: resolve @babel/traverse CJS interop for both native and vite contexts

The ssr.external approach only works for single-file runs, not the full
suite with isolate: false. Use runtime typeof check to handle both
native CJS resolution and vite's SSR transform.

Author: jdalton

.config/vitest.config.mts

@@ -24,10 +24,6 @@ if (isCoverageEnabled) {
 
 export default defineConfig({
   cacheDir: './.cache/vitest',
-  ssr: {
-    // Don't transpile CJS packages — let Node handle them natively
-    external: ['@babel/traverse'],
-  },
   test: {
     deps: {
       interopDefault: false,

test/unit/bundle-validation.test.mts

@@ -8,7 +8,10 @@ import path from 'node:path'
 import { fileURLToPath } from 'node:url'
 
 import { parse } from '@babel/parser'
-import traverse from '@babel/traverse'
+import _traverse from '@babel/traverse'
+
+// @babel/traverse CJS exports { default: fn } — resolve for both native and vite contexts
+const traverse = typeof _traverse === 'function' ? _traverse : _traverse.default
 import { describe, expect, it } from 'vitest'
 
 const __dirname = path.dirname(fileURLToPath(import.meta.url))