Module headers

Gateway-wide envelope header names (oag.*).

Protocol-owned names stay in their crates (stomp.*, agra.*). Bridging adapters stamp HDR_ORIGIN on the way in and call crate::Envelope::is_echo_of on the way out. The engine never reads these.

Constants

• HDR_ID
  Envelope crate::MessageId, written on outbound frames.
• HDR_ORIGIN
  Which adapter last published this envelope onto the engine.
• HDR_TOPIC
  Engine topic, copied onto a native frame when the protocol has a place for it.
• HDR_TYPE_HINT
  Engine type hint, copied onto a native frame when present.