How do I generate a PR summary?

I have local commits on a feature branch. How do I derive the PR title and the structured body from them?

1. Find the branch point against main:

   merge_base=$(git merge-base HEAD main)
   echo "branch point: ${merge_base}"
   

2. Collect commit messages since the branch point:

   git log --pretty=format:"%s" $(git merge-base HEAD main)..HEAD
   

3. Derive the title. Use the format [COMPONENT] Description. Pick the most representative commit, or combine if the PR spans multiple components (e.g. [trading,sql]).

4. Assemble the body. Use this skeleton:

   ## Summary
   
   One-paragraph summary: what changes, why.
   
   ## Changes
   
   - Bullet per material change, grouped if the PR spans components.
   
   ## Notes / Decisions
   
   - Anything non-obvious about the implementation.
   
   ## Captures
   
   - Captures filed while doing this work — bugs, limitations, or ideas
     noticed in passing and recorded with `compass capture` (they land in
     the product-backlog inbox). One Markdown link per line. Omit the
     section if there were none.
   

   Do not add a "Test plan" section — convention in this repo per CLAUDE.md.

No wrapper — the operations are bare git invocations.

Manual. Reviewers catch any divergence between commit set and PR summary.

• How do I create a PR? — the next step in the lifecycle.
• PR Manager — the skill that indexes the full PR lifecycle.