Apply Renovate PRs Locally

Collect every open pull request raised by Renovate in the target GitHub repository and apply their changes to the local working tree, so all dependency upgrades can be built and tested together.

Hard constraints

• Never run git commit, git push, git merge, git cherry-pick, git rebase, gh pr merge, gh pr close, or gh pr review.
• Do not create branches, tags, or worktrees unless the user asks.
• Do not modify anything on GitHub. Read-only gh commands only (gh pr list, gh pr view, gh pr diff, gh api GET).
• Leave the result as uncommitted changes in the working tree and report what was applied, so the user decides what to do next.

1. Check preconditions