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87ccfe3f6c
Replay and duplicate detection keyed on a 32-bit contentHashCode over at most the first 64 bytes of the payload. Two packets from the same peer in the same millisecond that agreed on that prefix were the same packet as far as this cache was concerned, and a collision here is a dropped message: the second is discarded and nothing reports it. PacketIdUtil is the identity the rest of the stack already uses for this question — gossip sync membership, and the message IDs MessageHandler assigns — and iOS derives it identically: first 16 bytes of SHA-256 over type, senderID, timestamp and the whole payload. The security path now agrees with the sync path instead of carrying a weaker private notion of "same packet", and the FRAGMENT special case disappears because the full payload is covered either way. Peer scoping is deliberately kept. PacketIdUtil covers the packet's own senderID, which is not the peer it arrived from once relayed.