Docs: Update SB11 migration notes for CSF tools

[valentinpalkovic]

Closes #

What I did

• Audited all pull requests merged between 2026-09-13 08:00 UTC and 2026-09-15 08:00 UTC. Nine landed on next; one landed on an experimental side branch.
• Documented the migration from the removed ConfigFile helpers in CSF: Add shared mutation API for stories and config files #36248 to the unified CsfObject API.
• Added the internal tooling change to the Storybook 11 migration guide. The remaining audited merges are fixes, tests, CI cleanup, documentation restructuring, or internal moves with no user migration step.

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!

1. Run yarn docs:check from the repository root and expect Docs check: no errors found.
2. Open docs/releases/migration-guide.mdx and follow the new Update custom CSF tooling to the unified mutation API link. Confirm it reaches the matching section in MIGRATION.md.
3. Compare the replacement table with code/core/src/csf-tools/ConfigFile.ts. Confirm that each Storybook 11 method and type exists and that the removed Storybook 10 names do not.

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

• Declare whether manual QA will be needed for this PR during the next release, through qa:needed or qa:skip

• 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.

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In-repo PRs: add the ci:canary label. Later pushes republish while the label remains.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Essentials

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📥 Commits

Reviewing files that changed from the base of the PR and between 06dc54c and c17f439.

📒 Files selected for processing (2)

• MIGRATION.md
• docs/releases/migration-guide.mdx

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Walkthrough

The migration documentation adds Storybook 11 guidance for custom CSF tooling. It describes replacing ConfigFile helpers with CsfObject methods and handling resolution results, mutation diagnostics, and writeConfig validation.

Changes

CSF tooling migration

Layer / File(s)	Summary
Unified mutation API guidance MIGRATION.md, docs/releases/migration-guide.mdx	The documentation lists the migration entry and describes replacing legacy helpers with getValue, set, and callArguments. It also documents mutation results, diagnostics, unresolved values, and writeConfig validation.

Priority: ⬇️ Low

Merge Risk: ⚪ Minimal · up to c17f4

The migration guidance changes do not introduce an identified production or user-facing risk and are ready to merge.

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