Restructure code that other people depend on without breaking them. Use when planning a large refactor or rewrite, splitting a monolith into packages, renaming or moving public symbols, changing internal architecture behind a stable API, or when the user says "I want to rewrite this" or "this code needs to be cleaned up". Covers strangler-fig migration, compatibility shims, codemods, feature flags, sequencing a refactor into reviewable PRs, and deciding when not to rewrite at all.
