RuntimeDefinitions: Add and use asAlpha

[anthony-murphy]

This pull request introduces a new utility function, asAlpha, to safely cast IContainerRuntimeBase to ContainerRuntimeBaseAlpha and exposes it throughout the codebase. This change simplifies and standardizes how alpha functionality is accessed in both production and test code, replacing direct type assertions with the new function. Several test files are updated to use asAlpha, improving type safety and clarity.

[Copilot]

Pull Request Overview

This pull request introduces a new utility function asAlpha to safely cast IContainerRuntimeBase to ContainerRuntimeBaseAlpha, standardizing how alpha functionality is accessed throughout the codebase. The change replaces direct type assertions with a centralized function, improving type safety and code clarity.

Key changes:

• Added asAlpha utility function in runtime-definitions package
• Updated multiple test files to use the new function instead of direct type casting
• Exported the function through the public API for broader usage

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/runtime/runtime-definitions/src/stagingMode.ts	Added the new asAlpha utility function
packages/runtime/runtime-definitions/src/index.ts	Exported the new function in the public API
packages/runtime/runtime-definitions/api-report/runtime-definitions.legacy.alpha.api.md	Updated API report to reflect the new export
packages/test/test-end-to-end-tests/src/test/stagingMode.spec.ts	Replaced direct type assertion with asAlpha function
packages/test/local-server-tests/src/test/stagingMode.spec.ts	Updated to use asAlpha instead of direct casting
packages/test/local-server-tests/src/test/documentDirty.spec.ts	Simplified casting logic using the new utility function
packages/test/local-server-stress-tests/src/stressDataObject.ts	Replaced manual type assertion with asAlpha

[github-actions]

🔗 No broken links found! ✅

Your attention to detail is admirable.

linkcheck output

> fluid-framework-docs-site@0.0.0 ci:check-links /home/runner/work/FluidFramework/FluidFramework/docs
> start-server-and-test "npm run serve -- --no-open" 3000 check-links

1: starting server using command "npm run serve -- --no-open"
and when url "[ 'http://127.0.0.1:3000' ]" is responding with HTTP status code 200
running tests using command "npm run check-links"


> fluid-framework-docs-site@0.0.0 serve
> docusaurus serve --no-open

[SUCCESS] Serving "build" directory at: http://localhost:3000/

> fluid-framework-docs-site@0.0.0 check-links
> linkcheck http://localhost:3000 --skip-file skipped-urls.txt

Crawling...

Stats:
  235713 links
    1720 destination URLs
    1953 URLs ignored
       0 warnings
       0 errors