Docs: Add 9 -> 10 migration guide

[kylegach]

What I did

• Add 9 -> 10 migration guide
• "From older version" is now 8 -> 9

Checklist for Contributors

Testing

Manual testing

1. Sync this branch with locally running docs site

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.

Greptile Summary

Updated On: 2025-09-03 16:25:58 UTC

This PR restructures Storybook's migration guide documentation to accommodate the upcoming Storybook 10 release. The changes involve shifting the migration guide hierarchy:

1. Updated primary migration guide (migration-guide.mdx): Now covers Storybook 9 → 10 migration, focusing on the key breaking changes in v10 which are primarily ESM-only distribution, updated Node.js requirements (20.19+ or 22.12+), and new features like CSF Next. The extensive package consolidation section from the previous v8→v9 guide has been removed since it's no longer relevant for v10.

2. Updated legacy migration guide (migration-guide-from-older-version.mdx): Now covers Storybook 8 → 9 migration (previously covered 7→8). This includes comprehensive documentation of the major package consolidation where many separate packages were merged into the main storybook package, breaking changes like dropped Vite 4 support, and framework-based configuration updates.

This restructuring follows Storybook's documentation pattern where the primary migration guide covers the latest version transition, while older migration paths are preserved as "from older version" guides. The changes ensure users have accurate migration information whether they're upgrading from v8 to v9 or v9 to v10, with appropriate level of detail for each transition's complexity.

Confidence score: 5/5

• This PR is safe to merge with minimal risk as it only updates documentation content
• Score reflects straightforward documentation restructuring with no code changes or functional modifications
• No files require special attention - both migration guides are well-structured and appropriately updated

[nx-cloud]

View your CI Pipeline Execution ↗ for commit d72eb3c

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☁️ Nx Cloud last updated this comment at 2025-09-03 16:57:47 UTC

[greptile-apps]

_{2 files reviewed, 2 comments}

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[shilman]

Looks good. Was going to comment on the Greptile suggestion, but you beat me to the punch! 🙌