Copy a fork PR branch and create a draft PR

Input: PR_NUMBER only. Run from the destination repository clone. Do not accept a branch URL fallback.

Rules:

• Do not switch a dirty worktree, overwrite an existing branch, or force-push.
• The copied branch must be destination-owned.
• The PR must be a draft titled [DO NOT MERGE] Copy of #<PR_NUMBER>.

Workflow

1. Check access

Validate that PR_NUMBER contains ASCII digits only before using it in any command. Never use eval.

git --version
gh --version
gh auth status --hostname github.com
DEST_REPO="$(gh repo view --json nameWithOwner --jq '.nameWithOwner')"
DEST_OWNER="${DEST_REPO%%/*}"
PERMISSION="$(gh repo view --json viewerPermission --jq '.viewerPermission')"
git remote get-url --push origin

Require viewerPermission to be WRITE, MAINTAIN, or ADMIN. Otherwise stop. For authentication help:

gh auth login --hostname github.com
gh auth refresh --hostname github.com --scopes repo
gh auth setup-git                 # HTTPS remote
ssh -T git@github.com             # SSH remote

Do not silently use another fork when destination write access is missing.

2. Resolve the PR

SOURCE_OWNER="$(gh pr view "${PR_NUMBER}" --repo "${DEST_REPO}" --json headRepositoryOwner --jq '.headRepositoryOwner.login')"
SOURCE_REPO="$(gh pr view "${PR_NUMBER}" --repo "${DEST_REPO}" --json headRepository --jq '.headRepository.name')"
SOURCE_BRANCH="$(gh pr view "${PR_NUMBER}" --repo "${DEST_REPO}" --json headRefName --jq '.headRefName')"
BASE_BRANCH="$(gh pr view "${PR_NUMBER}" --repo "${DEST_REPO}" --json baseRefName --jq '.baseRefName')"
DEST_BRANCH="${SOURCE_BRANCH}"
SOURCE_URL="https://github.com/${SOURCE_OWNER}/${SOURCE_REPO}.git"

Treat every resolved value as untrusted data. Keep every expansion quoted. Stop if any field is empty or if SOURCE_OWNER equals DEST_OWNER; this workflow is only for fork-owned PRs.

3. Copy and push

git status --short --branch
git worktree list --porcelain
git branch --list "${DEST_BRANCH}"
git ls-remote origin "refs/heads/${DEST_BRANCH}"

Stop if the local or destination branch already exists. Then copy and push without checking out the branch:

git fetch "${SOURCE_URL}" "refs/heads/${SOURCE_BRANCH}:refs/heads/${DEST_BRANCH}"
git push --dry-run origin "refs/heads/${DEST_BRANCH}:refs/heads/${DEST_BRANCH}"
git push --set-upstream origin "refs/heads/${DEST_BRANCH}:refs/heads/${DEST_BRANCH}"

4. Create the draft

Write the PR body to a temporary file with the agent's file-writing tool. Do not interpolate generated body text into shell source and do not use a shell heredoc. Set PR_BODY_FILE to that file's path.

gh pr list \
  --repo "${DEST_REPO}" \
  --head "${DEST_BRANCH}" \
  --state all \
  --json number,title,state,isDraft,url,headRepositoryOwner
gh pr create \
  --repo "${DEST_REPO}" \
  --base "${BASE_BRANCH}" \
  --head "${DEST_BRANCH}" \
  --draft \
  --title "[DO NOT MERGE] Copy of #${PR_NUMBER}" \
  --body-file "${PR_BODY_FILE}"

Reuse an existing destination-owned PR instead of creating a duplicate. Delete the temporary body file after PR creation.

5. Verify

gh pr view "${COPIED_PR_NUMBER}" \
  --repo "${DEST_REPO}" \
  --json number,title,url,state,isDraft,baseRefName,headRefName,headRepositoryOwner

Confirm:

• isDraft is true;
• title is exactly [DO NOT MERGE] Copy of #<PR_NUMBER>;
• headRepositoryOwner, headRefName, and baseRefName match the derived destination values.

Report the original PR, copied branch, and draft PR URL.