Three additions that together address asymmetric / one-way gossipsub
delivery seen on small (2-3 node) overlay networks where the default
gossipsub mesh sits below its low-watermark and AutoNAT v1 cannot
reach a stable reachability verdict:

  * libp2p AutoNAT v2 is now in defaultLibp2pOptions. v1 needs >=3 peers
    to give a stable answer, leaving 2-peer clusters stuck in Unknown
    reachability and degrading downstream behaviour (relay selection,
    hole punching, identify). v2 produces a verdict from a single peer.

  * Gossipsub now uses FloodPublish + PeerExchange by default. FloodPublish
    has the publisher flood to ALL connected peers rather than just mesh
    peers; in a 2-node network the mesh sits at 1 entry (Dlo=4), well
    below the healthy-mesh threshold, and standard mesh-only delivery
    becomes unreliable. PeerExchange lets peers gossip about each other
    and helps recover from one-way mesh links.

  * When bootstrap peers are configured, they are passed to gossipsub as
    DirectPeers so the router holds a persistent connection and bypasses
    mesh negotiation when delivering to them — guaranteeing publication
    reaches known/seed peers regardless of mesh state.

The hub.NewHub signature gains a variadic Option parameter so callers
can opt in to direct-peer pinning without forcing the dependency into
the hub package's API. node.startNetwork is the only in-tree caller
and wires bootstrap peers through automatically.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>