chore: automate Rust crate versioning in publish-ci

[janechu]

Pull Request

📖 Description

When npm run publish-ci runs, it now also handles the microsoft-fast-build Rust crate automatically via a new build/publish-rust.mjs script.

This is a revised version of #7373 that addresses all review comments.

Changes

build/publish-rust.mjs (new)

A Node.js script that:

1. Finds the latest Beachball-generated tag matching microsoft-fast-build_v* using git tag --list --sort=-version:refname, falling back to all history if none exists
2. Inspects git commits touching crates/microsoft-fast-build/ since that tag
3. Determines the version bump type using conventional commits:
   • BREAKING CHANGE / feat!: / fix!: / refactor!: / chore!: → major
   • feat: → minor
   • anything else → patch
4. Updates the version in crates/microsoft-fast-build/Cargo.toml
5. Runs cargo package and copies the .crate file to publish_artifacts/cargo/
6. Exits cleanly (no-op) if no relevant commits are found since the last release

package.json

Updated publish-ci to run the Rust script before beachball:

node build/publish-rust.mjs && beachball publish -y --no-publish

build/README.md and build/DESIGN.md (new)

Added documentation for the build utilities workspace.

Behavior

Scenario	Result
Commits touch crates/microsoft-fast-build/	Version bumped, crate packaged to publish_artifacts/cargo/
No commits to crate since last tag	Script exits cleanly, no changes

This mirrors the existing pattern: beachball → publish_artifacts/ (npm), new script → publish_artifacts/cargo/ (Rust).

Review comments addressed from #7373

• Header comment mismatch: Updated doc comment to document all major bump triggers (refactor!:, chore!:)
• Output directory: Changed from publish_artifacts_cargo/ to publish_artifacts/cargo/ (covered by existing .gitignore entry for publish_artifacts/)
• Tag format alignment: Consistent use of {package-name}_v{version} (underscore) format throughout
• Script ordering: Rust script runs before beachball so the Cargo.toml version bump is captured in the commit
• Tag lookup: Uses git tag --list --sort=-version:refname instead of constructing tag from Cargo.toml version

🎫 Issues

Supersedes #7373

👩‍💻 Reviewer Notes

No .gitignore changes are needed because publish_artifacts/ is already ignored and publish_artifacts/cargo/ falls under that pattern.

The script runs before beachball in publish-ci so the Cargo.toml version bump is included in the beachball commit.

📑 Test Plan

• All existing tests pass (10917 pass, 0 fail)
• npm run build succeeds
• Biome formatting/linting passes
• No change files required (this is a build tooling change, not a package change)

✅ Checklist

General

• I have included a change request file using $ npm run change
• I have added tests for my changes.
• I have tested my changes.
• I have updated the project documentation to reflect my changes.
• I have read the CONTRIBUTING documentation and followed the standards for this project.

⏭ Next Steps

• Close chore: automate Rust crate versioning in publish-ci #7373 once this PR is merged
• Validate the script in a real CI publish run
• Consider adding unit tests for the conventional commit parsing logic