Add a "Sender Behavior (Informational)" section to Section 17 that captures the cross-implementation conventions for how senders should behave above the wire format: - Path Learning: cache the reversed accumulated path from received flood-routed packets; replace only when the new path is at least as good (hash size, SNR threshold implementation-defined). - PATH_RETURN: proactive emission lets the original sender switch to direct routing without waiting for an explicit path probe. - Flood Fallback and Retries: track outstanding DMs by expected ack_crc, increment attempt on each retry, hold timestamp constant, fall back from direct to flood after N unacknowledged direct retries. - Transmission Priority (sender-originated) table: ACK > PATH > direct reply > flood reply > req/resp > group > advert. All of these are informational guidance; numeric tunings remain implementation-defined. Complements the existing forwarding-priority table. Validated against upstream meshcore-dev/MeshCore @ 1a7b361 (BaseChatMesh send/recv flow, Mesh::createPathReturn, handleReturnPathRetry). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>