Banner: Fix types to restrict leadingVisual to variants info and upsell

[siddharthkp]

Summary

The leadingVisual and deprecated icon props on Banner are only rendered when variant is info or upsell. For every other variant (critical, success, warning), the Banner ignores a custom visual and always renders its built-in variant icon.

Until now the types allowed leadingVisual/icon to be passed alongside any variant, so this compiled even though it does nothing at runtime:

<Banner variant="critical" leadingVisual={<SomeIcon />} title="Critical" />

This PR narrows BannerProps into a discriminated union so custom visuals are only accepted for the variants that actually render them. The type surface now matches the runtime behavior.

Rollout strategy

• Patch release (debatable but this is a type-only narrowing; runtime behavior is unchanged)
• Minor release
• Major release; if selected, include a written rollout or migration plan
• None; if selected, include a brief description as to why

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-ui

[changeset-bot]

🦋 Changeset detected

Latest commit: 9f72c79

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

Name	Type
@primer/react	Major
@primer/mcp	Patch

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

[github-actions]

⚠️ Action required

👋 Hi, this pull request contains changes to the source code that github/github-ui depends on. If you are GitHub staff, test these changes with github/github-ui using the integration workflow. If this doesn't work, you can also use the original workflow here. Check the integration testing docs for step-by-step instructions. Or, apply the integration-tests: skipped manually label to skip these checks.

To publish a canary release for integration testing, apply the Canary Release label to this PR.

[Copilot]

Pull request overview

This PR aligns @primer/react’s Banner TypeScript API with its existing runtime behavior by restricting custom visuals (leadingVisual and deprecated icon) to the info and upsell variants.

Changes:

• Refactored BannerProps into a discriminated union so leadingVisual/icon are only accepted for info/upsell.
• Updated unit tests and Storybook/Figma examples to comply with the new type restrictions (including @ts-expect-error cases to validate runtime fallback).
• Added a changeset documenting the breaking type change.

Show a summary per file

File	Description
packages/react/src/Banner/Banner.tsx	Converts BannerProps to a discriminated union restricting custom visuals to info/upsell.
packages/react/src/Banner/Banner.test.tsx	Adds @ts-expect-error coverage for disallowed prop combinations while asserting runtime fallback behavior.
packages/react/src/Banner/Banner.stories.tsx	Adjusts Playground rendering to only pass leadingVisual for info/upsell to satisfy the new types.
packages/react/src/Banner/Banner.figma.tsx	Updates Figma code-connect example to conditionally pass icon only for supported variants.
.changeset/banner-leading-visual-types.md	Adds a changeset for the type-surface change (currently marked as major).

Review details

• Files reviewed: 5/5 changed files
• Comments generated: 1
• Review effort level: Low

[primer-integration]

Integration test results from github/github-ui PR:

  CI Passed
  VRT Passed
  Projects Passed

All checks passed!