Migration Engineering

A migration is a controlled transition, not just the target design.

Workflow

Describe current state, target state, invariants that must survive, and the populations/versions that may coexist.
Identify additive/compatible expansion that allows old and new behavior to operate safely.
Define data movement/backfill, dual-read/write or translation behavior only when necessary.
Define verification and reconciliation before cutover.
Bound the cutover: entry conditions, success signal, abort/recovery path, and operator responsibility when relevant.
Delay destructive contraction until evidence shows old consumers/state are gone.
Mark irreversible steps explicitly. Do not promise rollback where only roll-forward or restore is credible.
Route schema/query implementation to database-engineering, contract semantics to api-design, platform mechanics to platform-engineering, and recovery evidence to reliability-engineering as needed.