Interface TwitchSocket

A minimal websocket the client drives — the test seam. The 'message' handler receives the frame text; 'close'/'error' handlers ignore the argument (a single signature keeps the interface trivially implementable by the real ws adapter and the test mock).

interface TwitchSocket {
close(): void;
on(event: "message" | "close" | "error", cb: (data: string) => void): void;
}