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-e2e/test/envelope.test.ts

@@ -0,0 +1,60 @@
+import { describe, expect, it } from 'vitest'
+import type { AeadAlg, E2EEnvelope } from 'relay-contracts'
+import { importAeadKey } from '../src/aead.js'
+import { MAX_FRAME_BYTES, decodeEnvelope, encodeEnvelope, nonceForSeq } from '../src/envelope.js'
+import { EnvelopeFormatError } from '../src/errors.js'
+import { sealFrame } from '../src/session.js'
+import { bytesToHex, hexToBytes } from './helpers.js'
+import envVector from './vectors/envelope.json' with { type: 'json' }
+
+function sample(seq: bigint): E2EEnvelope {
+  return {
+    seq,
+    nonce: new Uint8Array([1, 2, 3, 4]),
+    ciphertext: new Uint8Array([9, 8, 7]),
+    tag: new Uint8Array(16).fill(0xbb),
+  }
+}
+
+describe('T3 envelope codec (frozen relay-contracts shape, re-exported)', () => {
+  it('KAT: frozen vector encodes to exact wire bytes and decodes back', () => {
+    const key = importAeadKey(new Uint8Array(32).fill(5), 'aes-256-gcm', 'c2h')
+    const env = sealFrame(key, BigInt(envVector.seq), new TextEncoder().encode('wire codec vector'))
+    expect(bytesToHex(encodeEnvelope(env))).toBe(envVector.wire)
+    const decoded = decodeEnvelope(hexToBytes(envVector.wire))
+    expect(bytesToHex(decoded.nonce)).toBe(envVector.nonce)
+    expect(bytesToHex(decoded.ciphertext)).toBe(envVector.ciphertext)
+    expect(bytesToHex(decoded.tag)).toBe(envVector.tag)
+  })
+
+  it('round-trips and preserves seq as bigint past 2^53 (no float truncation)', () => {
+    const env = sample(2n ** 63n - 1n)
+    const decoded = decodeEnvelope(encodeEnvelope(env))
+    expect(decoded.seq).toBe(2n ** 63n - 1n)
+    expect(decoded).toEqual(env)
+  })
+
+  it('deterministic nonce = left-zero-padded big-endian seq', () => {
+    const gcm = nonceForSeq(1n, 'aes-256-gcm' as AeadAlg)
+    expect(gcm.length).toBe(12)
+    expect(gcm[11]).toBe(1)
+    expect(gcm.slice(0, 11).every((b) => b === 0)).toBe(true)
+    const xchacha = nonceForSeq(258n, 'xchacha20-poly1305' as AeadAlg)
+    expect(xchacha.length).toBe(24)
+    expect(xchacha[23]).toBe(2)
+    expect(xchacha[22]).toBe(1)
+  })
+
+  it('negative: truncated buffer / length mismatch → EnvelopeFormatError', () => {
+    expect(() => decodeEnvelope(new Uint8Array(5))).toThrow(EnvelopeFormatError)
+    const wire = encodeEnvelope(sample(0n))
+    expect(() => decodeEnvelope(wire.slice(0, wire.length - 1))).toThrow(EnvelopeFormatError)
+    const trailing = new Uint8Array(wire.length + 1)
+    trailing.set(wire)
+    expect(() => decodeEnvelope(trailing)).toThrow(EnvelopeFormatError)
+  })
+
+  it('security: a frame larger than the hard cap is rejected before allocation', () => {
+    expect(() => decodeEnvelope(new Uint8Array(MAX_FRAME_BYTES + 1))).toThrow(EnvelopeFormatError)
+  })
+})