Limit Vale CI to PR diff only

[ctauchen]

Summary

• Vale was scanning the entire repo on every PR, taking ~10 minutes
• Now computes changed .md/.mdx files from the PR diff and passes only those to Vale
• Skips all steps entirely if no markdown files changed

Test plan

• Open a PR that changes a few markdown files — verify Vale runs quickly and only reports on those files
• Open a PR with no markdown changes — verify the job skips gracefully

🤖 Generated with Claude Code

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[Copilot]

Pull request overview

Updates the Vale GitHub Actions workflow to lint only Markdown/MDX files changed in a pull request (instead of scanning the entire repository), aiming to significantly reduce CI runtime.

Changes:

• Fetch full git history and compute changed .md/.mdx files from the PR commit range.
• Gate Node/Yarn/Vale steps behind a “skip” output when no markdown files changed.
• Pass the computed changed-file list to errata-ai/vale-action@reviewdog.

[Copilot]

git diff is comparing ${{ github.event.pull_request.base.sha }} to ${{ github.event.pull_request.head.sha }} with a two-dot range. If the PR branch is behind the base branch, this will include changes that exist only on the base branch (not introduced by the PR), causing Vale to lint unrelated files and potentially report unrelated issues. Use a merge-base comparison (e.g., the three-dot range) so only changes introduced by the PR are included.

Suggested change

	FILES=$(git diff --name-only --diff-filter=d ${{ github.event.pull_request.base.sha }} ${{ github.event.pull_request.head.sha }} -- '*.md' '*.mdx' | tr '\n' ' ')
	FILES=$(git diff --name-only --diff-filter=d ${{ github.event.pull_request.base.sha }}...${{ github.event.pull_request.head.sha }} -- '*.md' '*.mdx' | tr '\n' ' ')

[Copilot]

The "Swap stuff" step still runs rg ... . across the whole repository. This can be a significant portion of the runtime and undermines the goal of limiting Vale CI to the PR diff. Consider restricting the search/replace to the changed markdown files list (and skipping entirely when that list is empty), rather than scanning ..

Suggested change

	rg -l0 '\$\[[^\]]*\]' -g '*.mdx' -g '*.md' . | xargs -0 perl -i -pe 's/\$\[[^\]]*\]/PICKLEVAR/g'
	FILES="${{ steps.changed.outputs.files }}"
	if [ -n "$FILES" ]; then
	rg -l0 '\$\[[^\]]*\]' -g '*.mdx' -g '*.md' -- $FILES | xargs -0 perl -i -pe 's/\$\[[^\]]*\]/PICKLEVAR/g'
	fi