Message Envelope - Archer Exchange

All client → server and server → client messages are single JSON objects (or MessagePack with the equivalent shape). There is no streaming framing on top of WebSocket frames — one logical message per frame.

Client → server: tagged by `op`

{ "op": "subscribe", "channels": ["orderbook", "trades"], "market": "<market_pubkey>" }

Server → client operation responses: tagged by `op`

{ "op": "subscribed", "channels": ["orderbook", "trades"], "market": "<market_pubkey>" }

Server → client channel data: tagged by `ch` + `type`

{ "ch": "orderbook", "type": "snapshot", "market": "<market_pubkey>", "...": "..." }

Distinguish the two on the client by checking for op (op response) vs ch (channel data).