Pi: The Safe Diff Reviewer

The Stack

Tested Against

Prerequisites

• Pi (MIT): `npm install -g --ignore-scripts @earendil-works/pi-coding-agent`
• A model key/subscription — Pi auto-detects the provider (e.g. `export ANTHROPIC_API_KEY=…`), only needed to run the review
• git (the diff source)

Steps

1. 1

   Scaffold a staged diff and prove the allowlist is read-only

   CI installs Pi, builds a repo with a real staged change, and asserts the exact allowlist from the workflow (`read,grep,find,ls`) genuinely excludes write/edit/bash — the structural guarantee that makes the reviewer safe, not a prompt asking nicely.

   export PI_CODING_AGENT_DIR="$PWD/.pi"
   pi --version >/dev/null || { echo "pi missing"; exit 1; }
   git init -q && git config user.email ci@flowstacks.xyz && git config user.name ci
   printf 'def add(a, b):\n    return a+b\n' > calc.py && git add calc.py && git commit -qm init
   printf 'def add(a, b):\n    return a + b\n' > calc.py && git add calc.py
   test -n "$(git diff --staged)" && echo "staged diff: non-empty"
   ALLOW="read,grep,find,ls"
   if echo "$ALLOW" | grep -qE '(^|,)(write|edit|bash)(,|$)'; then echo "ALLOWLIST NOT READ-ONLY"; exit 1; fi
   echo "allowlist read-only: $ALLOW (write,edit,bash excluded)"
   pi --help 2>&1 | grep -q -- "--tools" && echo "pi supports --tools allowlist"

2. 2

   Run the review (the model step, not checked by CI)

   Pipe the diff in: `git diff --staged | pi --tools read,grep,find,ls -p "Review this diff for bugs, security issues, and missing tests. Be concise."`. The allowlist means write/edit/bash are off, so it physically can't change your code. The review itself calls a model, so CI doesn't run it.