XPort (Wanchain Message Bridge) messages from OrbitWan's own index: each message's source and destination legs, the apps, the payload, the Storeman group that signed the delivery and any failed delivery attempts. key (a message id or any transaction of the message) answers that message; otherwise the newest messages first, filtered by chain (a captured chain key or XPort chain id), app (0x hex) or delivered, with limit (up to 25) and cursor. A leg OrbitWan does not hold is not_seen or not_indexed, never pending or failed.