Rebases a stacked-branch chain onto an updated base branch using gh-stack, guides through conflict resolution if needed, validates each branch, and pushes all updated branches. Creates PRs for any branch that lacks one, with fork-aware targeting. Works on repos with or without Stacked PRs enabled. Use when rebasing stacked stories or PRs onto main or another updated branch. Activated by commands: /start, /continue, /validate, /push.