The Command pattern

Undo and redo in a notes app, and a queue of payout jobs: why a bolted-on undo stops scaling, how Command turns a request into an object with execute and undo, what undo needs (an inverse or stored state), two stacks, macros and failed commands, queueing, logging and retrying a request safely with an id, dead letters, compensation instead of undo, and how Command differs from Strategy, callbacks, Memento and events.