Author or scope a first-party Nx migration. Use whenever code removes, renames, or deprecates an option/flag/executor/generator-schema field, changes a default, or bumps a dependency, and someone asks whether existing workspaces need a migration so they don't break on `nx migrate`/upgrade. Covers writing the colocated update-VER/NAME.{ts,spec.ts,md} set, the migrations.json entry (version, requires, implementation, prompt, documentation) or packageJsonUpdates group, and the AI-agent prompt/runbook .md for prompt-only or hybrid (generator + prompt) migrations. Also covers porting an upstream framework's own migrations into Nx. Invoke BEFORE writing, fixing, or editing any migration, migration prompt/runbook, or packageJsonUpdates group, and before concluding a breaking change needs no migration at all.