fix(builders): remove external option from workflow bundle to fix require() errors

[technopahadi]

Problem

When using packages like ai (Vercel AI SDK) in workflow code, users encounter a runtime error:

  ReferenceError: require is not defined
      at anonymous (../../node_modules/ai/src/telemetry/assemble-operation-name.ts:19:4)
      at Script.runInContext (node:vm:149:12)
      at runInContext (node:vm:301:6)

This regression was introduced in beta.40 when the external option was added to the workflow bundle esbuild config.

Root Cause

The workflow bundle is configured with:

• format: 'cjs' - because the VM expects CommonJS
• platform: 'neutral' - because it's neither Node.js nor browser
• external: this.config.externalPackages || [] - to externalize packages from serverExternalPackages

When a package is marked as external with format: 'cjs', esbuild generates require() calls for those packages:

  var import_api = require("@opentelemetry/api");
  var import_anthropic = require("@ai-sdk/anthropic");

However, the workflow VM created via vm.runInContext() does not have require() defined. Looking at packages/core/src/vm/index.ts, the VM context only provides:

  g.exports = {};
  g.module = { exports: g.exports };

There is no require function, so any externalized package fails at runtime.

Solution

Remove the external option from the workflow bundle esbuild config in createWorkflowsBundle(). This restores the behavior from before beta.40.

Instead of externalizing packages (which generates broken require() calls), we:

1. Bundle everything into the workflow bundle
2. Rely on createNodeModuleErrorPlugin() to catch Node.js builtin imports at build time with helpful error messages

Verification

Before fix (beta.40+):

  // In bundled workflow output
  var import_api = require("@opentelemetry/api");  // ❌ Fails at runtime

After fix:

  // In bundled workflow output - package is inlined, no require() call
  // ✅ Works at runtime

Breaking Change?

No. This restores the original behavior from beta.39 and earlier. Users who were affected by the require is not defined error will now have working workflows.

Test Case

1. Create a workflow that imports from ai package:

  import { convertToModelMessages } from 'ai';

  export async function myWorkflow() {
    'use workflow';
    // ... use convertToModelMessages
  }

2. Add ai to serverExternalPackages in Next.js config
3. Run next dev --turbopack -p 3001 or next build and trigger the workflow
4. Before fix: ReferenceError: require is not defined
5. After fix: Workflow executes successfully

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[vercel]

@technopahadi is attempting to deploy a commit to the Vercel Labs Team on Vercel.

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[pranaygp]

@technopahadi thanks for finding this and fixing it. Could you please resolve the DCO check and include a changeset?

Also it would be awesome to add an e2e test that ensures this doesn't regress again

[pranaygp]

also this change might in turn cause a regression to #731 (@TooTallNate)?

[Copilot]

Pull request overview

This PR fixes a workflow bundling regression where externalized packages caused require is not defined errors inside the workflow VM.

Changes:

• Remove the external option from the workflow esbuild config so that all dependencies are bundled into the workflow bundle.
• Add detailed inline comments explaining why external is not used for workflows and how createNodeModuleErrorPlugin() is relied on to catch Node.js builtin imports.

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[technopahadi]

@pranaygp Can you review the test?

[vercel]

Removal of external option breaks bundling of pseudo-packages like 'server-only' and 'client-only' in workflow bundles

[technopahadi]

@pranaygp @TooTallNate ?

[karthikscale3]

Thanks for submitting a PR. This needed a bit more handling and has been fixed with this change