DhtTokens

Write-token generation and verification for an inbound get_peers / announce_peer (and BEP-44 get/put) flow. This is the pure, network-free port of node::generate_token and node::verify_token (src/kademlia/node.cpp).

A write token is the node's promise that a querier really controls the address it announced from: the node hands one out in every get_peers/get reply and only accepts an announce_peer/put that echoes a still-valid token. libtorrent computes

token = SHA1( address_string ‖ secret ‖ info_hash )[0 .. 4)     // write_token_size = 4

and keeps two rolling secrets so a token minted just before a secret rotation is still accepted just after it: verify_token checks the current secret first, then the previous one (node.cpp lines 190-202). rotateSecret performs the same m_secret[1] = m_secret[0]; m_secret[0] = random shuffle that node::tick does every few minutes.

One deliberate deviation from libtorrent. Upstream hashes addr.address().to_string(), the textual form of the IP. commonMain's io.github.yuroyami.kitetorrent.peer.PeerAddress exposes no canonical literal accessor, and a textual form is anyway ambiguous (::1 vs 0:0:…:1). We instead hash the raw address bytes the datagram arrived with. This is strictly an internal, per-node secret hash whose only requirements are determinism and that it bind address to info-hash. The byte form satisfies both at least as well as the string form. Tokens are opaque to every other node, so this never has to interoperate with libtorrent's exact byte layout; it only has to round-trip against this node's own verify.

The token width is fixed at TOKEN_SIZE (4 bytes), matching write_token_size.