Status: IN
Command's undo mechanism requires engineering discipline along three independent concerns: hysteresis prevention (using Memento to avoid state drift from repeated undo/redo cycles), meaningless-undo filtering (Reversible() method to skip trivial operations like font-color changes to current color), and state-varying copy management (copying commands before history insertion when state differs across invocations).
Three independent engineering concerns form a complete undo discipline
Depends on (SL): command-hysteresis-use-memento, command-reversible-prevents-meaningless-undo, command-undo-requires-copy-if-state-varies