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/src/aead-key.ts

@@ -0,0 +1,38 @@
+/**
+ * Internal opaque-key registry (P4 impl detail; NOT a re-declared contract shape).
+ *
+ * The frozen §4.4 `AeadKey` is a nominal phantom type (`{ readonly __aeadKey: unique symbol }`).
+ * At runtime we return an opaque, frozen handle and keep the real key material in a module-private
+ * WeakMap — the handle itself exposes NO bytes (supports INV5: no secret sitting on a passed object).
+ * `aadLabel` binds the direction/purpose into every frame's AEAD `aad = aadLabel‖seq`.
+ */
+import type { AeadAlg, AeadKey } from 'relay-contracts'
+import { AEAD_KEY_BYTES } from 'relay-contracts'
+import { E2EError } from './errors.js'
+
+export interface AeadKeyMaterial {
+  readonly raw: Uint8Array
+  readonly alg: AeadAlg
+  readonly aadLabel: string
+}
+
+const REGISTRY = new WeakMap<object, AeadKeyMaterial>()
+
+/** Wrap 32 raw key bytes + alg + aad label into the frozen opaque `AeadKey`. */
+export function wrapAeadKey(raw: Uint8Array, alg: AeadAlg, aadLabel: string): AeadKey {
+  if (raw.length !== AEAD_KEY_BYTES) {
+    throw new E2EError('E2E_KEY_LENGTH', `AEAD key must be ${AEAD_KEY_BYTES} bytes; got ${raw.length}`)
+  }
+  const handle = Object.freeze({})
+  REGISTRY.set(handle, { raw: raw.slice(), alg, aadLabel })
+  return handle as unknown as AeadKey
+}
+
+/** Recover the key material for a handle previously produced by {@link wrapAeadKey}. */
+export function unwrapAeadKey(key: AeadKey): AeadKeyMaterial {
+  const material = REGISTRY.get(key as unknown as object)
+  if (!material) {
+    throw new E2EError('E2E_BAD_KEY_HANDLE', 'value is not a relay-e2e AeadKey handle')
+  }
+  return material
+}