Recipe E — PR description auto-writer

Outcome: A PR_BODY.md file populated by passing your branch's git diff through Claude Sonnet with a project-specific system prompt. Plug into gh pr create --body-file PR_BODY.md.

Approx cost: ~$0.04 per PR.

Setup — one-time

Create a project system prompt at .github/prompts/pr-description.md:

copyYou are writing a pull request description for the visa-mono monorepo.

Structure the output as:

## Summary
- 2-3 bullets describing what the PR does and why.

## What changed
- file: short rationale per file.

## Test plan
- bulleted checklist of how the reviewer should verify.

Match the existing PR style on the repo. Be specific about the why
(non-obvious constraints, past incidents, drift this prevents). Don't
re-explain what the code already says.

Script

copy#!/bin/bash
set -euo pipefail

BASE="${1:-main}"

git diff "origin/$BASE...HEAD" \
  | visa-cli run-llm --json --yes - \
      --model or-claude-sonnet \
      --system @.github/prompts/pr-description.md \
      --max-tokens 4000 \
  | jq -r '.text' > PR_BODY.md

echo "Wrote PR_BODY.md ($(wc -l < PR_BODY.md) lines)"
echo "Open the PR with: gh pr create --body-file PR_BODY.md"

Cost breakdown

Variations

• Lower-cost — swap or-claude-sonnet for or-claude-haiku (~$0.005).
• Self-review — pipe the PR_BODY through run-llm again with a system prompt asking it to flag missing test plans, ambiguous wording, or missing context.
• Stacked PRs — feed git diff origin/main...HEAD for the full stack vs git diff origin/PREV_PR...HEAD for the incremental.