Fix preview links showing unrelated content changes#185
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Diff against the merge commit's first parent (HEAD~1) instead of origin/main. The merge ref can be stale when main moves forward, causing files added to main after the PR was opened to appear in the preview links.
cwickham
requested review from
gregswinehart,
ivelasq and
jeroenjanssens
as code owners
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Summary
HEAD~1) instead oforigin/mainwhen detecting content changes for preview linksContext
The
detect-contentjob checks outrefs/pull/N/mergethen diffs against a freshly fetchedorigin/main. When main has moved ahead since the merge ref was last updated, files added to main show up as "changed" — producing preview links for content the PR didn't touch.For example, PR #173 only changes
/people/hannah-frick/but got a preview link to/blog/2026-03-30_rag-with-raghilda/(added to main after the PR was opened).Since
refs/pull/N/mergeis a merge commit, its first parent (HEAD~1) is the base branch state at merge time. Diffing against that gives exactly the PR's changes.Test plan