MCP over CoAP (custom)

This is an experimental binding, not an MCP-standard transport.

• Endpoint: confirmable POST coap://host:5683/mcp
• Request and response payload: one exact MCP JSON-RPC UTF-8 message
• Content-Format: application/json (CoAP number 50)
• Correlation: JSON-RPC ID; CoAP token and message ID remain transport concerns
• Discovery: GET /.well-known/core advertises </mcp>;ct=50;rt="mcp.server"
• Reliability: normal CoAP CON retransmission
• Large payloads: libcoap-managed Block1 request reassembly and Block2 response
• Maximum size: the MCP request limit and configured CoAP response limit; oversized bodies fail explicitly
• Cancellation/streaming: request/response only; no Observe mapping is claimed

Example:

coap-client -m post -t application/json \
  -e '{"jsonrpc":"2.0","id":1,"method":"server/discover","params":{"_meta":{"io.modelcontextprotocol/protocolVersion":"2026-07-28","io.modelcontextprotocol/clientCapabilities":{}}}}' \
  coap://127.0.0.1:5683/mcp

libcoap remains an optional external dependency. DTLS configuration belongs to libcoap and its TLS backend, not the MCP core.