feat(relay): rendezvous-relay service — 7 packages + plans (contracts/transport/agent/control-plane/e2e/auth/web)

Multi-tenant reverse-tunnel service ("ngrok for Claude Code" with E2E): a
host-agent dials OUT to an operator-run relay; external devices reach the host
THROUGH the relay, routed by per-tenant subdomain, forwarding ciphertext only
(the relay never sees plaintext). Lets a customer reach their own self-hosted
web-terminal from anywhere with zero networking setup.

Packages — all tsc-strict + vitest green (656 tests), cross-package integration verified:
- relay-contracts: frozen shared contracts (mux frame codec, data model,
  capability token, E2E envelope, pairing) — the src/types.ts analog
- term-relay:   native WS mux + stateless data plane (subdomain routing, ciphertext forward)
- agent:        host-agent (pairing, per-host Ed25519 + mTLS dial-out, forwards to 127.0.0.1:3000)
- control-plane: accounts/hosts registry, pairing-code flow, routing table, provisioning
- relay-e2e:    browser<->agent E2E (X25519 ECDH through relay, AEAD, anti-replay, recoverable replay key)
- relay-auth:   Passkey/WebAuthn, capability tokens, per-host certs, deny-by-default tenant isolation
- relay-web:    browser login + Web Crypto E2E + client-side preview rendering

Security invariants INV1-15 enforced; cross-tenant isolation CI tripwire live
(.github/workflows/relay-tripwire.yml). Design + implementation-level plans in
docs/PLAN_RELAY_*.md and docs/EXPLORE_RELAY_SERVICE.md.

NOTE: generated autonomously per the reviewed plans. The security-critical
packages (relay-e2e, relay-auth) REQUIRE expert security audit before any real
deployment — passing tests prove self-consistency, not resistance to attackers.
Base app (src/, public/) unchanged; concurrent desktop work left uncommitted.

agent/test/heartbeat.test.ts

@@ -0,0 +1,58 @@
+import { describe, expect, it } from 'vitest'
+import { decodeMuxFrame } from 'relay-contracts'
+import { holdTunnel } from '../src/transport/tunnel.js'
+import { createHeartbeat, HEARTBEAT_INTERVAL_MS } from '../src/transport/heartbeat.js'
+import { FakeWs, FakeTimer } from './fixtures/fakes.js'
+
+describe('Heartbeat (T9, §4.1)', () => {
+  it('replies PONG echoing the inbound PING token byte-exact', () => {
+    const ws = new FakeWs()
+    const tunnel = holdTunnel(ws)
+    const hb = createHeartbeat(tunnel, { timer: new FakeTimer() })
+    const token = new Uint8Array([1, 2, 3, 4, 5, 6, 7, 8])
+    hb.onPing(token)
+    const frame = decodeMuxFrame(ws.sent.at(-1)!)
+    expect(frame.header.type).toBe('pong')
+    expect(Buffer.from(frame.payload).equals(Buffer.from(token))).toBe(true)
+  })
+
+  it('fires onDead when no PONG arrives within the interval', () => {
+    const ws = new FakeWs()
+    const tunnel = holdTunnel(ws)
+    const timer = new FakeTimer()
+    const hb = createHeartbeat(tunnel, { timer, intervalMs: 1000 })
+    let dead = false
+    hb.onDead(() => {
+      dead = true
+    })
+    hb.start() // sends first ping, arms deadline
+    timer.advance(1000) // deadline fires, no pong seen
+    expect(dead).toBe(true)
+  })
+
+  it('does not fire onDead when PONG arrives in time', () => {
+    const ws = new FakeWs()
+    const tunnel = holdTunnel(ws)
+    const timer = new FakeTimer()
+    const hb = createHeartbeat(tunnel, { timer, intervalMs: 1000, genToken: () => new Uint8Array(8) })
+    let dead = false
+    hb.onDead(() => {
+      dead = true
+    })
+    hb.start()
+    hb.onPong(new Uint8Array(8)) // clears pending before the deadline
+    timer.advance(1000)
+    expect(dead).toBe(false)
+  })
+
+  it('exposes the frozen 15s interval', () => {
+    expect(HEARTBEAT_INTERVAL_MS).toBe(15_000)
+  })
+
+  it('stop() cancels timers (no leak)', () => {
+    const ws = new FakeWs()
+    const hb = createHeartbeat(holdTunnel(ws), { timer: new FakeTimer(), intervalMs: 1000 })
+    hb.start()
+    expect(() => hb.stop()).not.toThrow()
+  })
+})