S5: Compact envelope format for constrained links:
- 16-byte truncated addresses (MeshAddress) instead of 32-byte keys
- 16-byte truncated content ID
- u16 TTL and u32 timestamp (smaller than V1)
- Priority field (Low/Normal/High/Emergency)
- ~30-50 bytes savings per envelope vs V1
Full public keys are exchanged during announce phase and cached in
routing table. Envelope only needs addresses for routing.
Christian Nennemann
9cbf824db6