Scripts: Log error cause for generate task

[huang-julien]

Closes #

What I did

When Aa generate task fails, there's no information on what error caused the task to fail;

This PR adds source errors to throwned errors

Checklist for Contributors

Testing

The changes in this PR are covered in the following automated tests:

• stories
• unit tests
• integration tests
• end-to-end tests

Manual testing

Caution

This section is mandatory for all contributions. If you believe no manual test is necessary, please state so explicitly. Thanks!

Documentation

• Add or update documentation reflecting your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Checklist for Maintainers

• When this PR is ready for testing, make sure to add ci:normal, ci:merged or ci:daily GH label to it to run a specific set of sandboxes. The particular set of sandboxes can be found in code/lib/cli-storybook/src/sandbox-templates.ts

• Make sure this PR contains one of the labels below:

  Available labels

  • bug: Internal changes that fixes incorrect behavior.
  • maintenance: User-facing maintenance tasks.
  • dependencies: Upgrading (sometimes downgrading) dependencies.
  • build: Internal-facing build tooling & test updates. Will not show up in release changelog.
  • cleanup: Minor cleanup style change. Will not show up in release changelog.
  • documentation: Documentation only changes. Will not show up in release changelog.
  • feature request: Introducing a new feature.
  • BREAKING CHANGE: Changes that break compatibility in some way with current major version.
  • other: Changes that don't fit in the above categories.

🦋 Canary release

This PR does not have a canary release associated. You can request a canary release of this pull request by mentioning the @storybookjs/core team here.

core team members can create a canary release here or locally with gh workflow run --repo storybookjs/storybook publish.yml --field pr=<PR_NUMBER>

Summary by CodeRabbit

• Chores
  • Improved error handling in sandbox generation with enhanced error cause tracking, providing better diagnostics when yarn setup or generation failures occur.

[coderabbitai]

📝 Walkthrough

Walkthrough

The pull request improves error propagation in the sandbox generation script by adding Error cause objects to thrown errors. Yarn setup failures and sandbox generation failures now preserve and attach underlying error objects, enabling better error context and debugging information throughout the failure chain.

Changes

Error Cause Propagation

Layer / File(s)	Summary
Yarn Setup Error Cause scripts/sandbox/generate.ts	When yarn setup fails, the thrown error now includes the underlying caught error as a cause property instead of discarding it.
Generation Failure Error Propagation scripts/sandbox/generate.ts	When sandbox generation fails (both in the immediate throw for non-CI/STORYBOOK_SANDBOX_GENERATE environments and the deferred throw after GitHub Actions summary), aggregated "Some sandboxes failed to generate" errors now include a cause containing rejected generation results' underlying error objects.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

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[coderabbitai]

🧹 Nitpick comments (1)

scripts/sandbox/generate.ts (1)

334-341: ⚡ Quick win

Consider using AggregateError instead of an array in cause.

Passing an array of errors as the cause property is non-standard. Error monitoring and logging tools typically expect Error.cause to be a single Error object, not an array. Node.js provides AggregateError (available since v15.0.0) specifically for representing multiple errors.

♻️ Refactor to use AggregateError

-      throw new Error(`Some sandboxes failed to generate`, {
-        cause: generationResults
-          .filter((result) => result.status === 'rejected')
-          .map((result) => {
-            const generationError = (result as PromiseRejectedResult).reason as Error;
-            return generationError;
-          }),
-      });
+      throw new AggregateError(
+        generationResults
+          .filter((result) => result.status === 'rejected')
+          .map((result) => (result as PromiseRejectedResult).reason),
+        'Some sandboxes failed to generate'
+      );

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@scripts/sandbox/generate.ts` around lines 334 - 341, Replace the thrown Error
that uses an array in its cause with an AggregateError: collect the rejected
promises from generationResults (the current .filter/.map that produces
generationError from PromiseRejectedResult) into an array of Error objects and
throw new AggregateError(errorsArray, 'Some sandboxes failed to generate')
instead of throw new Error(...); ensure you remove the array-as-cause usage and
reference the existing generationResults and generationError variables when
building the AggregateError.

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@scripts/sandbox/generate.ts`:
- Around line 334-341: Replace the thrown Error that uses an array in its cause
with an AggregateError: collect the rejected promises from generationResults
(the current .filter/.map that produces generationError from
PromiseRejectedResult) into an array of Error objects and throw new
AggregateError(errorsArray, 'Some sandboxes failed to generate') instead of
throw new Error(...); ensure you remove the array-as-cause usage and reference
the existing generationResults and generationError variables when building the
AggregateError.

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 7602194f-caf2-4e83-a29d-b40ab69a5549

📥 Commits

Reviewing files that changed from the base of the PR and between b2167d6 and f8ad130.

📒 Files selected for processing (1)

• scripts/sandbox/generate.ts

[storybook-app-bot]

Package Benchmarks

^{Commit: f8ad130, ran on 9 May 2026 at 11:59:33 UTC}

The following packages have significant changes to their size or dependencies:

@storybook/cli

	Before	After	Difference
Dependency count	194	194	0
Self size	906 KB	890 KB	🎉 -16 KB 🎉
Dependency size	84.49 MB	84.49 MB	🚨 +1 KB 🚨
Bundle Size Analyzer	Link	Link