fix(builders): Inline Next.js pseudo‑packages and strip server-only/client-only requires in workflow bundles (#911)

* Fix bundling behavior for dynamic imports and server-only, client-only imports

* Generate changeset

* Filter tsconfig to only pull in code from within the current working directory(workflow dir)

* Rewrite server-only and client-only

* add additional pseudo directives

* upmerge

* fix failing unit test

Author: karthikscale3

.changeset/fix-pseudo-package-bundling.md

@@ -0,0 +1,5 @@
+---
+"@workflow/builders": patch
+---
+
+Fix workflow bundle to inline pseudo-packages instead of marking them external

packages/builders/src/base-builder.ts

@@ -14,6 +14,7 @@ import {
 } from './apply-swc-transform.js';
 import { createDiscoverEntriesPlugin } from './discover-entries-esbuild-plugin.js';
 import { createNodeModuleErrorPlugin } from './node-module-esbuild-plugin.js';
+import { createPseudoPackagePlugin } from './pseudo-package-esbuild-plugin.js';
 import { createSwcPlugin } from './swc-esbuild-plugin.js';
 import type { WorkflowConfig } from './types.js';
 import { extractWorkflowGraphs } from './workflows-extractor.js';
@@ -371,6 +372,9 @@ export abstract class BaseBuilder {
       // occur in deeply nested function calls across multiple files.
       sourcemap: 'inline',
       plugins: [
+        // Handle pseudo-packages like 'server-only' and 'client-only' by providing
+        // empty modules. Must run first to intercept these before other resolution.
+        createPseudoPackagePlugin(),
         createSwcPlugin({
           mode: 'step',
           entriesToBundle: externalizeNonSteps
@@ -539,6 +543,9 @@ export abstract class BaseBuilder {
         '.cjs',
       ],
       plugins: [
+        // Handle pseudo-packages like 'server-only' and 'client-only' by providing
+        // empty modules. Must run first to intercept these before other resolution.
+        createPseudoPackagePlugin(),
         createSwcPlugin({
           mode: 'workflow',
           workflowManifest,
@@ -547,8 +554,14 @@ export abstract class BaseBuilder {
         // happens first, preventing false positives on Node.js imports in unused code paths
         createNodeModuleErrorPlugin(),
       ],
-      // External packages that should not be bundled (e.g., server-only, client-only for Next.js)
-      external: this.config.externalPackages || [],
+      // NOTE: We intentionally do NOT use the external option here for workflow bundles.
+      // When packages are marked external with format: 'cjs', esbuild generates require() calls.
+      // However, the workflow VM (vm.runInContext) does not have require() defined - it only
+      // provides module.exports and exports. External packages would fail at runtime with:
+      //   ReferenceError: require is not defined
+      // Instead, we bundle everything and rely on:
+      // - createPseudoPackagePlugin() to handle server-only/client-only with empty modules
+      // - createNodeModuleErrorPlugin() to catch Node.js builtin imports at build time
     });
     const interimBundle = await interimBundleCtx.rebuild();
 

packages/builders/src/index.ts

@@ -10,6 +10,10 @@ export {
 export { STEP_QUEUE_TRIGGER, WORKFLOW_QUEUE_TRIGGER } from './constants.js';
 export { createDiscoverEntriesPlugin } from './discover-entries-esbuild-plugin.js';
 export { createNodeModuleErrorPlugin } from './node-module-esbuild-plugin.js';
+export {
+  createPseudoPackagePlugin,
+  PSEUDO_PACKAGES,
+} from './pseudo-package-esbuild-plugin.js';
 export { NORMALIZE_REQUEST_CODE } from './request-converter.js';
 export { StandaloneBuilder } from './standalone.js';
 export { createSwcPlugin } from './swc-esbuild-plugin.js';