ARC0003: External command handler

What

An undecorated class declares handle(command: DecoratedCommand). Rule: arc-core/arc0003 (requires type information).

Why

Arc executes handle() on the command instance, not an external handler class. This rule checks a directly typed @command() class, not indirect aliases.

Bad

export class RegisterHandler { handle(command: Register) {} }

Good

@command()
export class Register { handle() {} }