Add beta entry point to core-utils

[CraigMacomber]

Description

Add beta entry point to core-utils: it has a beta API now (as ofd #27282), and the changeset for that API documents using it via this previously non existent entry point.

Reviewer Guidance

The review process is outlined on this wiki page.

[github-actions]

Hi! Thank you for opening this PR. Want me to review it?

Based on the diff (26 lines, 5 files), I've queued these reviewers:

• Correctness — logic errors, race conditions, lifecycle issues
• Security — vulnerabilities, secret exposure, injection
• API Compatibility — breaking changes, release tags, type design
• Performance — algorithmic regressions, memory leaks
• Testing — coverage gaps, hollow tests

How this works

• Adjust the reviewer set by ticking/unticking boxes above. Reviewer toggles alone don't trigger anything.

• Tick Start review below to dispatch the review fleet.

• After review finishes, tick Start review again to request another run — it auto-resets after each dispatch.

• This comment updates as new commits land; your reviewer selections are preserved.

• Start review

[Copilot]

Pull request overview

Adds a /beta entrypoint to @fluidframework/core-utils so beta-tagged APIs can be consumed via exports-based subpath imports, aligning it with other packages that already support public/alpha/beta/legacy entrypoints.

Changes:

• Add ./beta to @fluidframework/core-utils package.json#exports and wire up export-lint scripts for beta.
• Document the new beta import path in @fluidframework/core-utils README.
• Add API Extractor lint configs for the new beta entrypoint.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
packages/framework/fluid-framework/src/index.ts	Removes an explanatory comment around the onAssertionFailure re-export.
packages/common/core-utils/README.md	Documents importing beta APIs from @fluidframework/core-utils/beta.
packages/common/core-utils/package.json	Adds ./beta export mapping and beta export-lint scripts.
packages/common/core-utils/api-extractor/api-extractor-lint-beta.esm.json	Adds API Extractor lint config for ESM beta entrypoint.
packages/common/core-utils/api-extractor/api-extractor-lint-beta.cjs.json	Adds API Extractor lint config for CJS beta entrypoint.

[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:
  288859 links
    1925 destination URLs
    2175 URLs ignored
       0 warnings
       0 errors