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.

agent/test/replaySeal.test.ts

@@ -0,0 +1,72 @@
+import { describe, expect, it, vi } from 'vitest'
+import type { AeadKey, E2EEnvelope, ReplayKeyParams } from 'relay-contracts'
+import { createReplaySealer, type ReplayCrypto } from '../src/e2e/replaySeal.js'
+
+/** Fake AEAD: key = tagged secret‖sessionId; ciphertext = plaintext XOR keyByte (marker hidden). */
+function fakeCrypto(): ReplayCrypto & { derivations: ReplayKeyParams[] } {
+  const derivations: ReplayKeyParams[] = []
+  return {
+    derivations,
+    deriveContentKey(params: ReplayKeyParams): AeadKey {
+      derivations.push(params)
+      const tag = new TextEncoder().encode(`${Buffer.from(params.hostContentSecret).toString('hex')}:${params.sessionId}`)
+      return tag as unknown as AeadKey
+    },
+    sealReplayFrame(key: AeadKey, seq: bigint, plaintext: Uint8Array): E2EEnvelope {
+      const kb = (key as unknown as Uint8Array)[0] ?? 0x5a
+      const ciphertext = plaintext.map((b) => b ^ kb)
+      return { seq, nonce: new Uint8Array([Number(seq & 0xffn)]), ciphertext, tag: new Uint8Array([0xaa]) }
+    },
+  }
+}
+
+const SECRET = new Uint8Array([1, 2, 3, 4])
+
+describe('createReplaySealer (T19, FIX 3)', () => {
+  it('derives K_content deterministically from (secret, sessionId, alg)', () => {
+    const c1 = fakeCrypto()
+    createReplaySealer(SECRET, 'sess-1', 'aes-256-gcm', c1)
+    const c2 = fakeCrypto()
+    createReplaySealer(SECRET, 'sess-1', 'aes-256-gcm', c2)
+    expect(c1.derivations[0]).toEqual(c2.derivations[0])
+  })
+
+  it('a different sessionId → a different key (per-session separation)', () => {
+    const c = fakeCrypto()
+    createReplaySealer(SECRET, 'sess-1', 'aes-256-gcm', c)
+    createReplaySealer(SECRET, 'sess-2', 'aes-256-gcm', c)
+    expect(c.derivations[0]!.sessionId).not.toBe(c.derivations[1]!.sessionId)
+  })
+
+  it('emits a monotonic seq (INV13) and never leaks the plaintext marker (INV2)', () => {
+    const sealer = createReplaySealer(SECRET, 'sess-1', 'aes-256-gcm', fakeCrypto())
+    const marker = new TextEncoder().encode('SECRET-MARKER')
+    const e0 = sealer.seal(marker)
+    const e1 = sealer.seal(marker)
+    expect(e0.seq).toBe(0n)
+    expect(e1.seq).toBe(1n)
+    expect(Buffer.from(e0.ciphertext).includes(Buffer.from(marker))).toBe(false)
+  })
+
+  it('replay seal is DISTINCT from a live h2c seal for the same plaintext (FIX 3)', () => {
+    const replay = createReplaySealer(SECRET, 'sess-1', 'aes-256-gcm', fakeCrypto())
+    // model a live seal with a different key byte
+    const liveKey = new Uint8Array([0x11]) as unknown as AeadKey
+    const live = fakeCrypto().sealReplayFrame(liveKey, 0n, new Uint8Array([0x41, 0x42]))
+    const rep = replay.seal(new Uint8Array([0x41, 0x42]))
+    expect(Buffer.from(rep.ciphertext).equals(Buffer.from(live.ciphertext))).toBe(false)
+  })
+
+  it('the hostContentSecret is never mutated', () => {
+    const secret = new Uint8Array([9, 9, 9])
+    const spy = vi.fn()
+    createReplaySealer(secret, 's', 'aes-256-gcm', {
+      deriveContentKey: (p) => {
+        spy(p.hostContentSecret)
+        return new Uint8Array([1]) as unknown as AeadKey
+      },
+      sealReplayFrame: (_k, seq, pt) => ({ seq, nonce: new Uint8Array(), ciphertext: pt, tag: new Uint8Array() }),
+    })
+    expect([...secret]).toEqual([9, 9, 9])
+  })
+})