ServerEnvelope
ServerEnvelope =
MaelstromResponseMessage|HistoryResponseMessage|AssistantMessageResultMessage|EngineErrorMessage
Defined in: packages/protocol/src/lib/envelope.ts:385
Every message an engine host may send to a client over the duplex stream:
a decision MaelstromResponseMessage, a HistoryResponseMessage,
or an EngineErrorMessage. Discriminated on type.