stacked-pr-review-per-base-diff-and-attach

Stacked PR review: per-base diffs + base-branch attachment

Problem

Reviewing a stack of N dependent PRs (where #B is based on #A, #C is based on #B, etc., rather than each PR being based on main) hits two distinct issues:

1. Diff capture for reviewer agents. If you naively run gh pr diff <N> against every PR in the stack, gh defaults to comparing against the PR's declared base — which is correct. But if you pre-filter via git diff main..pr-branch, you'll include all upstream PRs' changes in the "downstream PR's diff," and reviewers will flag findings against code that actually shipped 2 PRs ago. The reviewer attributes the finding to the wrong PR, and the author of the downstream PR is left confused.

2. Where to commit the review reports. Once 3 reviewer agents have produced reviewer_correctness.md, reviewer_architecture.md, reviewer_security.md, they need to live somewhere reachable by every PR in the stack — but committing them to the top-of-stack PR pollutes that PR's diff (the reports become "changes" the topmost PR is making). The base-of-stack PR is the natural home.

Context / Trigger Conditions

• A stack of 2+ open PRs exists where the head PR's base is another open PR (not main)
• You're dispatching a multi-agent review panel (e.g., roundtable:agent-review-panel) to cover the whole stack
• One of these symptoms:
  • Reviewer flags a "missing feature" in PR #C that was actually added in PR #A
  • Reviewer's diff snapshot shows ~3× as many lines as the PR's actual change
  • You want PR #A's reviewer to see the docs/reviews/ folder but committing it to PR #C's branch means PR #A can't see it
  • The orchestrator wonders "which branch do I commit this report to?"

Solution

Pattern 1: per-PR base-aware diff capture

For each PR in the stack, capture its diff against ITS OWN base, not against main:

mkdir -p /tmp/stack-review
for pr in 57 58 59; do
  # gh pr diff defaults to PR's declared base (the right thing)
  gh pr diff $pr -R <org>/agentic-ai-workshop \
    > /tmp/stack-review/pr${pr}-vs-its-base.diff
  # Also save the body so reviewers have author intent
  gh pr view $pr -R <org>/agentic-ai-workshop --json body -q .body \
    > /tmp/stack-review/pr${pr}-body.md
done
wc -l /tmp/stack-review/*.diff