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-web/test/preview-client.test.ts

@@ -0,0 +1,100 @@
+import { describe, expect, it, vi } from 'vitest'
+import { deriveContentKey, openReplayCiphertext, sealReplayFrame } from 'relay-e2e'
+import { randomBytes } from 'relay-e2e'
+import {
+  mountPreviewClient,
+  type PreviewDeps,
+  type ReadonlyTerminalLike,
+  type ReplaySource,
+} from '../src/preview-client'
+
+const HOST_SECRET = randomBytes(32)
+const SESSION_ID = 'sess-1'
+const ALG = 'aes-256-gcm' as const
+
+/** Seal a screen (as a P2 agent stub would) under K_content with sealReplayFrame. */
+function sealedReplay(lines: readonly string[], secret = HOST_SECRET): ReplaySource {
+  const k = deriveContentKey({ hostContentSecret: secret, sessionId: SESSION_ID, alg: ALG })
+  const frames = lines.map((line, i) =>
+    // sealReplayFrame → E2EEnvelope, encoded to a DATA payload the browser opens.
+    // openReplayCiphertext decodes+opens; we mirror the encode via the session envelope codec.
+    encodeReplayFrame(sealReplayFrame(k, BigInt(i), new TextEncoder().encode(line))),
+  )
+  return { sessionId: SESSION_ID, alg: ALG, frames }
+}
+
+// The replay codec: relay-e2e's openReplayCiphertext expects the encoded envelope bytes.
+import { encodeEnvelope } from 'relay-e2e'
+function encodeReplayFrame(env: ReturnType<typeof sealReplayFrame>): Uint8Array {
+  return encodeEnvelope(env)
+}
+
+const realDeps: PreviewDeps = { deriveContentKey, openReplayCiphertext }
+
+function mockTerminal(): ReadonlyTerminalLike & { written: string[] } {
+  const written: string[] = []
+  return { written, open: () => {}, write: (d) => written.push(d), dispose: () => {} }
+}
+
+describe('mountPreviewClient (T9)', () => {
+  it('recoverable-key decrypt: sealReplayFrame frames render into the read-only xterm (FIX 3)', async () => {
+    const card = document.createElement('div')
+    const term = mockTerminal()
+    const client = mountPreviewClient(
+      card,
+      sealedReplay(['line-A', 'line-B']),
+      HOST_SECRET,
+      { cols: 80, rows: 24 },
+      { ...realDeps, createTerminal: () => term },
+    )
+    await client.render()
+    expect(term.written).toEqual(['line-A', 'line-B'])
+  })
+
+  it('wrong/host-mismatched secret → openReplayCiphertext throws → "unavailable", never garbled', async () => {
+    const card = document.createElement('div')
+    const term = mockTerminal()
+    const replay = sealedReplay(['secret-screen']) // sealed under HOST_SECRET
+    const client = mountPreviewClient(
+      card,
+      replay,
+      randomBytes(32), // a DIFFERENT host secret → derives a different K_content
+      { cols: 80, rows: 24 },
+      { ...realDeps, createTerminal: () => term },
+    )
+    await client.render()
+    expect(card.querySelector('.preview-unavailable')?.textContent).toBe('unavailable')
+    expect(term.written).toEqual([]) // never wrote a torn screen
+  })
+
+  it('read-only: the preview terminal exposes NO input path (no onData/send)', async () => {
+    const card = document.createElement('div')
+    const term = mockTerminal()
+    mountPreviewClient(
+      card,
+      sealedReplay(['x']),
+      HOST_SECRET,
+      { cols: 80, rows: 24 },
+      { ...realDeps, createTerminal: () => term },
+    ).render()
+    expect('onData' in term).toBe(false)
+    expect('send' in term).toBe(false)
+  })
+
+  it('never writes hostContentSecret to localStorage/console', async () => {
+    const spy = vi.spyOn(console, 'log').mockImplementation(() => {})
+    const card = document.createElement('div')
+    await mountPreviewClient(
+      card,
+      sealedReplay(['x']),
+      HOST_SECRET,
+      { cols: 80, rows: 24 },
+      { ...realDeps, createTerminal: () => mockTerminal() },
+    ).render()
+    expect(spy).not.toHaveBeenCalled()
+    expect(JSON.stringify(localStorage)).not.toContain(
+      Array.from(HOST_SECRET.slice(0, 4)).join(','),
+    )
+    spy.mockRestore()
+  })
+})