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.

term-relay/test/heartbeat.test.ts

@@ -0,0 +1,74 @@
+import { describe, test, expect, vi } from 'vitest'
+import {
+  createHeartbeat,
+  HEARTBEAT_INTERVAL_MS,
+  HEARTBEAT_MISS_LIMIT,
+  type ScheduleHandle,
+} from '../mux/heartbeat.js'
+
+/** A manually-driven fake scheduler: `tick()` fires the scheduled callback; cancel stops it. */
+function fakeScheduler() {
+  let scheduled: (() => void) | null = null
+  const schedule = (fn: () => void): ScheduleHandle => {
+    scheduled = fn
+    return { cancel: () => (scheduled = null) }
+  }
+  return { schedule, tick: () => scheduled?.() }
+}
+
+describe('heartbeat (T5, §4.1 15s PING/PONG)', () => {
+  test('start sends a PING immediately with a fresh 8-byte token', () => {
+    const { schedule } = fakeScheduler()
+    const pings: Uint8Array[] = []
+    const hb = createHeartbeat({ schedule, sendPing: (t) => pings.push(t), onDead: () => {} })
+    hb.start()
+    expect(pings).toHaveLength(1)
+    expect(pings[0]!.length).toBe(8)
+  })
+
+  test('a matching onPong resets the miss counter; 3 misses ⇒ onDead exactly once', () => {
+    const sched = fakeScheduler()
+    const pings: Uint8Array[] = []
+    const onDead = vi.fn()
+    const hb = createHeartbeat({ schedule: sched.schedule, sendPing: (t) => pings.push(t), onDead })
+    hb.start() // ping #1, outstanding set
+    hb.onPong(pings[0]!) // matched → miss counter reset
+    sched.tick() // outstanding was cleared → no miss, ping #2
+    sched.tick() // miss 1, ping #3
+    sched.tick() // miss 2, ping #4
+    sched.tick() // miss 3 → dead
+    expect(onDead).toHaveBeenCalledTimes(1)
+    const pingsAfterDead = pings.length
+    sched.tick() // no further pings after dead
+    expect(pings.length).toBe(pingsAfterDead)
+  })
+
+  test('a stale/unknown PONG token does NOT reset the miss counter (anti-replay)', () => {
+    const sched = fakeScheduler()
+    const onDead = vi.fn()
+    const hb = createHeartbeat({ schedule: sched.schedule, sendPing: () => {}, onDead })
+    hb.start()
+    hb.onPong(new Uint8Array([9, 9, 9, 9, 9, 9, 9, 9])) // wrong token — ignored
+    sched.tick() // miss 1
+    sched.tick() // miss 2
+    sched.tick() // miss 3 → dead despite the spoofed PONG
+    expect(onDead).toHaveBeenCalledTimes(1)
+  })
+
+  test('stop cancels cleanly (no onDead after stop)', () => {
+    const sched = fakeScheduler()
+    const onDead = vi.fn()
+    const hb = createHeartbeat({ schedule: sched.schedule, sendPing: () => {}, onDead })
+    hb.start()
+    hb.stop()
+    sched.tick() // scheduler cancelled → no-op
+    sched.tick()
+    sched.tick()
+    expect(onDead).not.toHaveBeenCalled()
+  })
+
+  test('exposes the §4.1 constants', () => {
+    expect(HEARTBEAT_INTERVAL_MS).toBe(15_000)
+    expect(HEARTBEAT_MISS_LIMIT).toBe(3)
+  })
+})