Add a "Multipart ACK Usage Constraints" subsection making explicit
what upstream enforces in code but the spec previously left implicit:
- MULTIPART-wrapped ACKs MUST only be emitted on direct-routed return
paths. When no direct path is known, the sender MUST fall back to a
plain PAYLOAD_TYPE_ACK via flood. Matches sendAckTo() and
routeDirectRecvAcks() in upstream.
- All MULTIPART and plain copies of the same ACK carry an identical
4-byte ack_crc; receivers MUST dedup by CRC at the application
layer (Section 16 packet-hash dedup does not catch them because the
wrapper byte makes each copy hash-distinct).
- Typical inter-copy delay ~300 ms plus the direct retransmit delay;
exact count via getExtraAckTransmitCount() (reference default 0).
Validated against upstream meshcore-dev/MeshCore @ 1a7b361
(Mesh::routeDirectRecvAcks, BaseChatMesh::sendAckTo).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
swaitsandClaude Opus 4.7
1c2007dcb5