Scope Discovery: Custom Kad-DHT + Connection Gating

[sunwavesun]

Problems

1. Nodes discover unrelated ecosystems via broad/public discovery, leading to thousands of extra peers and off-namespace PubSub subscriptions.
2. Resource pressure (FDs/CPU/memory) correlates with dial failures like failed to negotiate security protocol: EOF.

Rationale

A custom Kad-DHT protocol prefix isolates our routing table from the public DHT and keeps discovery Harmony-only.

Connection gating blocks or immediately tears down non-Harmony peers at the transport layer (pre-dial/accept and post-identify), preserving capacity for legitimate Harmony traffic.

Changes

• Add config for a Harmony-scoped DHT prefix (default: /harmony/kad/1.0.0) and use only configured Harmony bootnodes.
• Implement connection gating:
  • Pre-dial / inbound-accept policy to allow only vetted peers/addresses (e.g., Harmony bootnodes/validators).
  • Post-identify filter: require advertised Harmony protocol IDs / chain marker; close non-conforming peers and purge their addrs from the peerstore.
  • Basic metrics/logging for gated/closed peers to validate effectiveness.

Notes:
No changes to PubSub topics, scoring, or connmgr here (follow-ups if needed).

Rollout

1. Bootnodes first: enable dual-prefix (old + new) to avoid partitions.
2. Validators/regular nodes: switch to the new prefix; verify peer counts and dial success.
3. Converge (a new PR required): remove the old prefix on bootnodes after majority adoption.
4. Enable connection gating in “observe” or permissive mode (log only), then tighten to enforce close policies once metrics look healthy.

Success criteria

• Peerstore and active connections drop to expected ranges; off-namespace subscriptions materially reduced.
• Non-Harmony peers are rejected at connect or immediately post-identify (visible in gating metrics).
• Dial success rate to Harmony peers improves; handshake EOFs materially reduced.

[mur-me]

Hey, tests are failing with

p2p/host.go:394:31: cannot use disc.GetRawDiscovery() (value of type []"github.com/libp2p/go-libp2p/core/discovery".Discovery) as "github.com/libp2p/go-libp2p/core/discovery".Discovery value in argument to libp2p_pubsub.WithDiscovery: []"github.com/libp2p/go-libp2p/core/discovery".Discovery does not implement "github.com/libp2p/go-libp2p/core/discovery".Discovery (missing method Advertise)