Refactor pipeline

Some refactors matter a lot and nobody wants to do them: splitting a crate that has grown to half a million lines, extracting modules, migrating every caller of an API. The work is mechanical but long. It's too big to review as one PR, and too tedious to babysit for a week.

This skill runs it as three lanes that never talk to each other. Each lane has one job and its own cadence. Git is the message bus, and the PR stack is the shared state.

PRODUCER  ──push every commit──▶  source branch  ──▶  PACKAGER  ──adds PRs──▶  PR stack  ◀──  SHEPHERD
(one split per commit,                               (rebase, test,                        (conflicts, CI,
 reports vs a fixed baseline)                         reviewable PRs)                       review threads)
                    ▲                                                                           │
                    └──────── daily: rebase onto what landed, drop merged commits ◀─────────────┘

You set the target, merge what's green, and route context between lanes when one of them needs to know something the others learned. The lanes do the rest.

When to use