net: add experimental HNS node rendezvous and relay

[denuoweb]

Summary

• limit this draft to the first HNSR layer: outbound-only full nodes receiving ordinary relayed Handshake peer sessions through HNS_NODE_V1
• add a private HNSR envelope, rendezvous and relay capability bits, strict packet/state bounds, and a regtest-only feature gate
• implement iterative rendezvous discovery, replicated unnamed-node routes, two-relay reservation lifecycle and failover, bounded circuits, flow control, and inner Brontide
• exercise ordinary hsd peers, 1,000 pings, and a real mined block over the inner relayed connection

Deliberate split

The earlier version of this PR combined node rendezvous, named-service authorization, a web profile, and later routing hardening. This draft now stops before the named-service commit so the node transport can be reviewed independently.

• review branch and exact commit: https://github.com/denuoweb/hsd/tree/2fc40f1c61ff16a2f39d9514cd950d1560430ced
• retained named-service/web checkpoint, not submitted for upstream review: hnsr: retain named-service and web checkpoint denuoweb/hsd#2
• retained full Phase 2 research stack, not submitted for upstream review: hnsr: retain Phase 2 routing hardening checkpoint denuoweb/hsd#3
• protocol discussion: HIP: Handshake P2P Rendezvous and Authenticated Service Relay HIPs#78

Named-service authorization and browser/web transport will be proposed separately only after the node-rendezvous layer receives review.

Scope and safety

The experiment is opt-in, disabled outside regtest, and does not forward to a requester-selected host or port. A circuit terminates only at the live peer connection bound to its signed reservation. Private values 0x04000000, 0x08000000, and 0xf3 are collision-prone test values, not requests for permanent assignments.

Validation

NODE_BACKEND=js npm run test-file -- \
  test/hnsr-test.js test/brontide-test.js test/net-test.js

NODE_BACKEND=js node scripts/run-hnsr-regtest-trial.js \
  docs/hnsr-regtest-phase1.json

• focused HNSR, Brontide, and network suites: 65 passing
• eight independently keyed FullNodes on regtest
• four-copy publication with recovery after rendezvous loss
• reservation renewal, withdrawal, disconnect invalidation, and stale-ticket rejection
• automatic first-relay failure fallback
• an ordinary inner hsd peer session carrying 1,000 pings and a real block
• bounded admission and relay queues with zero drops in the checked trial

Program relationship

See the canonical program architecture and review order.

[denuoweb]

@nodech — requesting review of the node-rendezvous layer, especially route admission, reservation lifecycle, circuit flow control, and interaction with ordinary peer traffic. Named-service and web layers have been removed from this PR.