net: exchange signed .btf descriptors between peers (#32)

Discovery has depended entirely on the Nostr relays. Two connected nodes never
told each other who else existed, so a relay outage left a running network
unable to grow, and a node that found one stale peer had no way to learn there
was anything better. The old `addr` gossip went out with the IRC seed.

Peers now trade signed descriptors over a new "btfpeers" message: our own
first, then peers that actually answered us. The receiver checks each Schnorr
signature against the key the `.btf` address decodes to, so the sender is
trusted for nothing -- forging an entry needs somebody else's secret key. That
leaves flooding with self-generated keys, which the per-message caps and the
"peers that answered" ordering are there to blunt.

Unknown commands are ignored (main.cpp), so nodes without this just drop the
message; nothing here is a protocol break.

The cache from the peer-cache change now keeps each peer's descriptor verbatim
alongside the parsed fields, because that signature is what makes a peer
relayable. Entries without one -- resolved through Nostr, or written before
this -- stay dialable, just not passed on. A dial never clears a descriptor
already on file.

0 files changed, 0 insertions, 0 deletions