Core: Various fixes

[ghengeveld]

What I did

Added some missing ARIA labels and prevented accessing a property of undefined.

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

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 canary-release-pr.yml --field pr=<PR_NUMBER>

Greptile Summary

Accessibility and defensive programming improvements in core UI components, focusing on ARIA labels and null handling.

• Added aria-label to Modal close button in code/core/src/components/components/Modal/Modal.styled.tsx for better screen reader support
• Added aria-label to 'Create new story' button in code/core/src/manager/components/sidebar/Sidebar.tsx improving sidebar accessibility
• Fixed potential undefined error in getDescendantIds function by adding null coalescing for entry.children in code/core/src/manager/utils/tree.ts

[greptile-apps]

_{3 files reviewed, 1 comment
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[nx-cloud]

View your CI Pipeline Execution ↗ for commit 0ab7802.

Command	Status	Duration	Result
nx run-many -t check -c production --parallel=7	✅ Succeeded	1m 9s	View ↗
nx run-many -t build -c production --parallel=3	✅ Succeeded	4m 20s	View ↗

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☁️ Nx Cloud last updated this comment at 2025-06-30 13:56:09 UTC

[storybook-app-bot]

Package Benchmarks

^{Commit: 0ab7802, ran on 30 June 2025 at 14:00:23 UTC}

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

storybook

	Before	After	Difference
Dependency count	51	51	0
Self size	31.72 MB	31.73 MB	🚨 +16 KB 🚨
Dependency size	17.43 MB	17.43 MB	0 B
Bundle Size Analyzer	Link	Link

sb

	Before	After	Difference
Dependency count	52	52	0
Self size	1 KB	1 KB	0 B
Dependency size	49.15 MB	49.16 MB	🚨 +16 KB 🚨
Bundle Size Analyzer	Link	Link

@storybook/cli

	Before	After	Difference
Dependency count	217	217	0
Self size	582 KB	582 KB	0 B
Dependency size	94.75 MB	94.77 MB	🚨 +16 KB 🚨
Bundle Size Analyzer	Link	Link

@storybook/codemod

	Before	After	Difference
Dependency count	186	186	0
Self size	31 KB	31 KB	0 B
Dependency size	78.85 MB	78.86 MB	🚨 +16 KB 🚨
Bundle Size Analyzer	Link	Link