prepare-branch-context

name	prepare-branch-context
description	Build read-only context for the current branch or pull request before follow-up work. Use when the user asks what a branch does, asks for PR context, inherits an unclear branch, or wants to continue work from an existing branch.

Prepare Branch Context

Use this before changing an inherited branch. The skill is read-only.

Precedence

User instructions and docs/canon.md are authoritative. If worktree discovery applies, inspect worktrees before assuming the current checkout is the whole state.

Workflow

1. Identify the branch and repository:

git status -sb
git branch --show-current
git remote -v

2. Detect the base branch in this order:

• PR base from gh pr view --json baseRefName,headRefName,url,state;
• remote default from git symbolic-ref -q refs/remotes/origin/HEAD;
• main;
• master.

3. Inspect branch changes:

BASE_BRANCH="$(gh pr view --json baseRefName --jq .baseRefName 2>/dev/null || true)"
if [ -z "$BASE_BRANCH" ]; then
  ORIGIN_HEAD="$(git symbolic-ref -q --short refs/remotes/origin/HEAD 2>/dev/null || true)"
  BASE_BRANCH="${ORIGIN_HEAD#origin/}"
fi
if [ -z "$BASE_BRANCH" ]; then
  if git rev-parse --verify origin/main >/dev/null 2>&1; then
    BASE_BRANCH="main"
  elif git rev-parse --verify origin/master >/dev/null 2>&1; then
    BASE_BRANCH="master"
  elif git rev-parse --verify main >/dev/null 2>&1; then
    BASE_BRANCH="main"
  else
    BASE_BRANCH="master"
  fi
fi
if git rev-parse --verify "origin/$BASE_BRANCH" >/dev/null 2>&1; then
  BASE="origin/$BASE_BRANCH"
else
  BASE="$BASE_BRANCH"
fi

git diff "$BASE"...HEAD --stat
git diff "$BASE"...HEAD
git log --oneline "$BASE"..HEAD

4. Inspect PR context when available:

if PR_DATA="$(gh pr view --json number,title,body,url,state,comments,reviews,reviewDecision,statusCheckRollup 2>/dev/null)"; then
  printf '%s\n' "$PR_DATA"
  NUMBER="$(printf '%s\n' "$PR_DATA" | jq -r .number)"
  REPO="$(gh repo view --json nameWithOwner --jq .nameWithOwner)"
  gh api "repos/$REPO/pulls/$NUMBER/comments"
fi

5. Report:

• purpose of the branch,
• base branch used and how it was detected,
• key files and areas affected,
• notable decisions or patterns,
• open comments or review findings,
• tracked changes, staged changes, untracked files, and unpushed commits.

Rules

• Do not edit files.
• Do not assume main when PR metadata or remote default says otherwise.
• Do not collapse dirty worktree state and unpushed commits into one status.
• If the diff is large, read the full structure first, then inspect the highest-impact files in detail.