Simplify resizable API: use persist: false | 'localStorage' | fn

[Copilot]

Consolidates resizable prop configuration from separate {persist: false} and {save: fn} patterns into unified {persist: false | 'localStorage' | fn} API.

Changelog

Changed

• resizable prop now accepts {persist: false | 'localStorage' | fn} instead of separate {persist: false} and {save: fn} configs
• Renamed CustomPersistConfig → PersistConfig
• Renamed NoPersistConfig → removed (merged into PersistConfig)
• Custom persistence functions now passed via persist property instead of save

Before:

<PageLayout.Pane resizable={{save: (w) => store(w)}} />

After:

<PageLayout.Pane resizable={{persist: (w) => store(w)}} />
// Explicit localStorage now possible:
<PageLayout.Pane resizable={{persist: 'localStorage'}} />

New

• PersistFunction type for custom persistence
• isCustomPersistFunction type guard
• isPersistConfig type guard

Removed

• NoPersistConfig type (merged into PersistConfig)
• CustomPersistConfig type (replaced by PersistConfig)
• isNoPersistConfig type guard
• isCustomPersistConfig type guard

Rollout strategy

• Patch release
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

Note: While this changes the API surface, the original PR hasn't been released yet, so this is effectively a pre-release refinement.

Testing & Reviewing

• Updated 66 unit tests to use new API
• Updated Storybook examples demonstrating all three persist modes
• Type checking passes with new signatures

Merge checklist

• Added/updated tests
• Added/updated documentation
• Added/updated previews (Storybook)
• Changes are SSR compatible
• Tested in Chrome
• Tested in Firefox
• Tested in Safari
• Tested in Edge
• (GitHub staff only) Integration tests pass at github/github (Learn more about how to run integration tests)

---

✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[changeset-bot]

⚠️ No Changeset found

Latest commit: 679e98e

Merging this PR will not cause a version bump for any packages. If these changes should not result in a new version, you're good to go. If these changes should result in a version bump, you need to add a changeset.

This PR includes no changesets

When changesets are added to this PR, you'll see the packages that this PR includes changesets for and the associated semver types

Click here to learn what changesets are, and how to add one.

Click here if you're a maintainer who wants to add a changeset to this PR