[masquare]

Reviews a PR together with its whole stack as one combined diff, so a design problem in a lower PR can surface once upper PRs build on it.

• Finds the stack from open PRs: walks base branches down to the target branch and follows every open PR built on top. One review and one comment per bottom-to-top path.
• Checks out the top branch, points a local base branch at the bottom PR's target, and runs PR-Agent's local provider on that diff. The PR list is passed to the model so findings name the owning PR.
• Posts one sticky comment on the triggering PR, edited in place on reruns. Per-PR inline suggestions stay in pr-agent.yaml (ci: add PR-Agent review workflow using OpenRouter #766).
• The script and config run from the default branch, never from the PR under review. Same-repo, non-draft PRs only.
• Triggers: opened, reopened, ready for review, and manual workflow_dispatch with a PR number.

Status: stack detection checked with a unit-style assertion. A local dry run on the #758/#759 stack built the 23.8k-token combined diff, but deepseek returned a truncated empty answer for it, so end-to-end output is not verified yet.