Module wire 

The PEX wire — the four type-tagged JSON messages (SPEC §4) and their framing.

The four messages

type	Purpose
pex_handshake	first message each direction: version + network + declared interval + own flags (§4.2)
pex_snapshot	the first data message: a capped picture of the sender’s first-hand set (§4.3)
pex_delta	the periodic message: added / dropped relative to what this link was told (§4.4)
pex_error	the advisory error envelope (§4.5)

Framing (SPEC §4.1)

• Byte stream (node↔node, §10.1): PexMessage::encode / PexMessage::decode frame each message as a u32 big-endian length prefix + JSON body — byte-identical to the dig-nat / dig-dht wires. A length prefix over crate::caps::PEX_MAX_FRAME is rejected without allocating the body.
• Relay WebSocket (relay→node, §10.2): PexMessage::to_json / PexMessage::from_json carry the bare JSON object in one WebSocket text frame (the socket already delimits messages).

JSON shapes are frozen: the type tags and field names are the wire contract, and unknown fields are ignored on receive (additive evolution).

Enums

PexMessage

A PEX protocol message — one of the four type-tagged shapes (SPEC §4). The type tag and field names are the frozen wire contract.