Constant REPLICATION_PROTOCOL_ID 

pub const REPLICATION_PROTOCOL_ID: &str = "autonomi.ant.replication.v2";

Protocol identifier for replication operations.

Bumped to v2 for the v12 storage-bound audit. That change extends the wire types (NeighborSyncRequest/Response carry an optional trailing StorageCommitment, and the gossip-triggered storage-commitment audit adds the SubtreeAuditChallenge/SubtreeAuditResponse and SubtreeByteChallenge/ SubtreeByteResponse messages). The bump is for SEMANTIC interop, not decode failure: postcard tolerates the appended optional field (an old decoder reads the fields it knows and ignores the trailer — pinned by the old_decoder_tolerates_new_neighbor_sync_* tests in protocol.rs), but tolerating bytes is not interoperating. A v1 node cannot decode the NEW message variants at all (unknown enum discriminant) and never acts on a piggybacked commitment, so mixed-version replication would half-function — audit challenges unanswered, commitments silently dropped — and a v2 node could read that silence as misbehaviour. Rather than reason about each such case, we route v12 replication on a distinct protocol id: a node only delivers messages whose topic matches its own id (see the topic check in mod.rs), so v1 and v2 nodes simply do not exchange replication traffic during a mixed-version window. This is the rollout-safe behaviour: no half-interpreted exchange, no spurious eviction. Replication between matched-version peers is unaffected. (DHT routing/lookups are a separate protocol and continue to span both versions.)