Interface CommandCallback<STATE, CONTEXT, ARGS>

The action a command runs. ARGS is the per-invocation input (execute(args)) — deliberately a separate type from STATE (the current model value the command reflects, read via getState()). They flow in opposite directions — STATE is output (command → UI, for display/enablement), args is input (UI → command) — and only coincidentally share a type (a font picker is STATE = string and ARGS = string). A toggle is STATE = boolean, ARGS = void (it just toggles). See design/COMMAND-DESIGN.md "arg vs state".