An implementation that stands up in a day: table, switch class, stable assignment. Where the switch sits, how it fits the database, and how it disappears again.
Turning twelve thousand messages into an order of work: three kinds of deprecation, the bottom-up route, and the rebuilds that never announce themselves.
The schema outlives every modernization of the code. The four legacy traits that are almost always there, what to measure first, and in what order to change.
