fix(builders): skip Node.js builtins in esbuild alias fallback

.changeset/fix-builtin-externalization.md

@@ -0,0 +1,5 @@
+---
+"@workflow/builders": patch
+---
+
+Skip Node.js builtins in esbuild alias fallback to prevent them from being relativized

packages/builders/src/swc-esbuild-plugin.test.ts

@@ -122,6 +122,42 @@ describe('createSwcPlugin externalizeNonSteps', () => {
     expect(output).not.toContain('@/lib/config');
   });
 
+  it('keeps Node.js builtins as bare specifiers when enhanced-resolve fails', async () => {
+    const outdir = join(testRoot, 'out');
+    const srcDir = join(testRoot, 'src');
+    const stepFile = join(srcDir, 'step.ts');
+
+    writeFile(
+      stepFile,
+      `import { randomUUID } from 'crypto';\nimport { join } from 'node:path';\nconsole.log(randomUUID(), join('a', 'b'));`
+    );
+
+    const result = await esbuild.build({
+      entryPoints: [stepFile],
+      absWorkingDir: testRoot,
+      outdir,
+      bundle: true,
+      format: 'esm',
+      platform: 'node',
+      write: false,
+      plugins: [
+        createSwcPlugin({
+          mode: 'step',
+          entriesToBundle: [stepFile],
+          outdir,
+        }),
+      ],
+    });
+
+    expect(result.errors).toHaveLength(0);
+    const output = result.outputFiles[0].text;
+    // Builtins must stay as bare specifiers, not be relativized
+    expect(output).toMatch(/from\s+["']crypto["']/);
+    expect(output).toMatch(/from\s+["']node:path["']/);
+    expect(output).not.toMatch(/from\s+["']\..*crypto/);
+    expect(output).not.toMatch(/from\s+["']\..*node:path/);
+  });
+
   it('does not externalize aliased imports that resolve into node_modules', async () => {
     const outdir = join(testRoot, 'out');
     const srcDir = join(testRoot, 'src');

packages/builders/src/swc-esbuild-plugin.ts

@@ -1,4 +1,5 @@
 import { readFile } from 'node:fs/promises';
+import { isBuiltin } from 'node:module';
 import { relative } from 'node:path';
 import { promisify } from 'node:util';
 import enhancedResolveOrig from 'enhanced-resolve';
@@ -142,6 +143,13 @@ export function createSwcPlugin(options: SwcPluginOptions): Plugin {
               specifier
             ).catch(() => undefined); // swallow so esbuild fallback below can try
 
+            // Node.js builtins (e.g. "crypto", "node:path") aren't resolvable
+            // by enhanced-resolve either, but must stay as bare specifiers —
+            // not be handed to esbuild's resolver which would relativize them.
+            if (!resolvedPath && isBuiltin(specifier)) {
+              return null;
+            }
+
             // Fall back to esbuild for aliases/tsconfig paths,
             // but only accept project-local results
             if (!resolvedPath) {