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.

relay-auth/test/device-proof.test.ts

@@ -0,0 +1,59 @@
+import { describe, it, expect, beforeEach } from 'vitest'
+import {
+  signDeviceAuthProof,
+  verifyDeviceProof,
+  deviceProofAccount,
+} from '../src/capability/device-proof.js'
+import { setupP5SigningKey, makeEphemeral, principal } from './_helpers.js'
+import { randomBytes } from 'node:crypto'
+
+const NOW = 1_700_000_000
+
+async function bindingA() {
+  return {
+    clientEphPub: new Uint8Array(randomBytes(32)),
+    clientNonce: new Uint8Array(randomBytes(24)),
+  }
+}
+
+describe('device-auth proof (§4.4 / §6b)', () => {
+  let signingKey: CryptoKey
+  beforeEach(async () => {
+    ;({ signingKey } = await setupP5SigningKey())
+  })
+
+  it('verifies a proof bound to THIS handshake (accountId asserted)', async () => {
+    const binding = await bindingA()
+    const proof = await signDeviceAuthProof(principal('acct-A'), binding, signingKey, NOW)
+    expect(await verifyDeviceProof(proof, binding, NOW)).toBe(true)
+    expect(deviceProofAccount(proof)).toBe('acct-A')
+  })
+
+  it('rejects a proof replayed into a DIFFERENT handshake (different clientEphPub)', async () => {
+    const bindingA1 = await bindingA()
+    const proof = await signDeviceAuthProof(principal('acct-A'), bindingA1, signingKey, NOW)
+    const bindingB = await bindingA() // fresh ephemeral / nonce
+    expect(await verifyDeviceProof(proof, bindingB, NOW)).toBe(false)
+  })
+
+  it('rejects a proof signed by a non-P5 key (unbound/forged bearer)', async () => {
+    const binding = await bindingA()
+    const other = await makeEphemeral()
+    const proof = await signDeviceAuthProof(principal('acct-A'), binding, other.privateKey, NOW)
+    // verify key is still P5's key from setup; other.privateKey is not P5's signer
+    expect(await verifyDeviceProof(proof, binding, NOW)).toBe(false)
+  })
+
+  it('rejects a tampered proof', async () => {
+    const binding = await bindingA()
+    const proof = await signDeviceAuthProof(principal('acct-A'), binding, signingKey, NOW)
+    const tampered = proof.slice(0, -2) + (proof.endsWith('AA') ? 'BB' : 'AA')
+    expect(await verifyDeviceProof(tampered, binding, NOW)).toBe(false)
+  })
+
+  it('rejects a stale proof (outside freshness window)', async () => {
+    const binding = await bindingA()
+    const proof = await signDeviceAuthProof(principal('acct-A'), binding, signingKey, NOW)
+    expect(await verifyDeviceProof(proof, binding, NOW + 10_000)).toBe(false)
+  })
+})