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-contracts/test/e2e-envelope.test.ts

@@ -0,0 +1,81 @@
+import { describe, expect, it } from 'vitest'
+import {
+  ContractDecodeError,
+  NONCE_BYTES,
+  decodeEnvelope,
+  encodeEnvelope,
+  nonceForSeq,
+  type E2EEnvelope,
+} from '../src/index.js'
+
+const sample = (over: Partial<E2EEnvelope> = {}): E2EEnvelope => ({
+  seq: 1n,
+  nonce: nonceForSeq(1n, 'aes-256-gcm'),
+  ciphertext: Uint8Array.of(0xde, 0xad, 0xbe, 0xef),
+  tag: new Uint8Array(16).fill(0x11),
+  ...over,
+})
+
+describe('§4.4 deterministic nonce = f(seq)', () => {
+  it('KAT: seq 0x0102 in the last 8 bytes of a 12-byte GCM nonce', () => {
+    expect([...nonceForSeq(0x0102n, 'aes-256-gcm')]).toEqual([
+      0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0x01, 0x02,
+    ])
+  })
+
+  it('produces the correct width per alg', () => {
+    expect(nonceForSeq(1n, 'aes-256-gcm').length).toBe(NONCE_BYTES['aes-256-gcm'])
+    expect(nonceForSeq(1n, 'xchacha20-poly1305').length).toBe(NONCE_BYTES['xchacha20-poly1305'])
+  })
+
+  it('is deterministic and collision-free across distinct seq', () => {
+    const a = nonceForSeq(5n, 'xchacha20-poly1305')
+    const b = nonceForSeq(5n, 'xchacha20-poly1305')
+    const c = nonceForSeq(6n, 'xchacha20-poly1305')
+    expect([...a]).toEqual([...b])
+    expect([...a]).not.toEqual([...c])
+  })
+})
+
+describe('§4.4 E2EEnvelope binary codec', () => {
+  it('KAT: encodes a known small envelope to a fixed byte vector', () => {
+    const env: E2EEnvelope = {
+      seq: 1n,
+      nonce: Uint8Array.of(1, 2, 3),
+      ciphertext: Uint8Array.of(0xaa),
+      tag: Uint8Array.of(0xbb),
+    }
+    expect([...encodeEnvelope(env)]).toEqual([
+      0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, // seq
+      0x03, // nonceLen
+      0x00, 0x00, 0x00, 0x01, // ciphertextLen
+      0x01, // tagLen
+      0x01, 0x02, 0x03, // nonce
+      0xaa, // ciphertext
+      0xbb, // tag
+    ])
+  })
+
+  it('round-trips a realistic envelope (identity)', () => {
+    const env = sample()
+    const decoded = decodeEnvelope(encodeEnvelope(env))
+    expect(decoded.seq).toBe(env.seq)
+    expect([...decoded.nonce]).toEqual([...env.nonce])
+    expect([...decoded.ciphertext]).toEqual([...env.ciphertext])
+    expect([...decoded.tag]).toEqual([...env.tag])
+  })
+
+  it('preserves a large 64-bit seq', () => {
+    const env = sample({ seq: 0xfffffffffffffff0n })
+    expect(decodeEnvelope(encodeEnvelope(env)).seq).toBe(0xfffffffffffffff0n)
+  })
+
+  it('rejects a truncated envelope header', () => {
+    expect(() => decodeEnvelope(Uint8Array.of(0, 1, 2))).toThrow(ContractDecodeError)
+  })
+
+  it('rejects a length mismatch (trailing/short bytes)', () => {
+    const bytes = encodeEnvelope(sample())
+    expect(() => decodeEnvelope(bytes.subarray(0, bytes.length - 1))).toThrow(/length mismatch/)
+  })
+})