Viewport: Prioritize story viewport globals and avoid user-global pollution

[ia319]

Closes #33831

What I did

• prioritize story viewport globals when story viewport globals exist
• remove story-to-user viewport global synchronization
• reset invalid viewport options only when no story viewport global exists

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

1. Copy the preview and stories code from the issue reproduction link into the sandbox.

• After running, switch between stories and observe the viewport.
• Use the button to reset the viewport or select another device, then switch between stories and observe.
• Pass viewport-related query parameters, then switch between stories and observe.

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

• Bug Fixes
  • Improved viewport value resolution to intelligently prioritize story-level configurations, ensuring more consistent and predictable behavior when managing viewport settings and rotation states.

[coderabbitai]

📝 Walkthrough

Walkthrough

This pull request restructures viewport global value resolution in the useViewport hook by implementing a two-tier precedence system that prioritizes story-level globals over user and global values. The reset behavior transitions from automatic to conditional, only resetting to defaults when no story-level viewport exists. Invalid option handling is updated to preserve story-level viewports rather than forcing value updates.

Changes

Cohort / File(s)	Summary
Viewport global resolution logic code/core/src/viewport/useViewport.ts	Reworked global value resolution to introduce story-level viewport priority via storyHasViewport, primaryGlobal, and secondaryGlobal. Replaced automatic URL-defined viewport reset with conditional logic. Changed invalid-option handling to only reset to defaults when no story-level viewport exists. Added defaultIsRotated flag (false) to normalizeGlobal calls across all sources.
Dependency updates package.json	Updated dependencies and/or scripts with 15 additions and 17 deletions.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• Viewport: Skip viewport validation before parameters load #33794 — Modifies useViewport.ts's validation and reset logic within the same useEffect that applies viewport globals.
• Core: Fix viewport args handling and reset option #33560 — Modifies useViewport.ts to restructure how viewport globals are normalized and updated, directly related to normalizeGlobal behavior changes.

✨ Finishing touches

• 📝 Generate docstrings

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