fix(kyaml): make drift exemptions gate-only

[arena-ai-coding-agent]

Summary

• Make the KYAML drift list exempt paths from --check only. use-kyaml and use-yaml now still convert and roll back bot-owned workflow files, matching the pilot's stated scope.
• Qualify the CLI's KYAML.Stats type and add CLI-level coverage for conversion, check exemption, and rollback.
• Exercise all 17 tracked YAML files in the parser corpus. Compare emitted YAML/KYAML values with the production YAML.jl reader for application-consumed files; leave GitHub workflow acceptance to real Actions runs.
• Correct the corpus count and add an upstream architecture / migration-risk audit. No source YAML files are reformatted and no application serializers or runtime behavior are changed.

Review focus

Please review the distinction between migration scope and canonicality-gate exemptions, and whether the semantic comparison boundary for GitHub workflow YAML is appropriate. The new audit maps upstream's defaults, mutable user overlays, generated files, serializer paths, and a staged adoption plan.

Validation

• bash scripts/check-spdx.sh — passed.
• bash scripts/check-format.sh — passed.
• git diff --check — passed.
• Julia tests were not run: Julia is unavailable in this sandbox.
• The PR's CI and Proofs workflows both ended in startup_failure with zero jobs (CI, Proofs). These runs provide no test verdict. Please diagnose the workflow-start failure and obtain an actual passing CI run before merging; this PR is not being represented as green.

[coderabbitai]

Important

Review skipped

Bot user detected.

To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Advanced

Run ID: 4e758418-a293-4288-8032-9e4f07781af8

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands.}