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-auth/src/audit/alert.ts

@@ -0,0 +1,19 @@
+/**
+ * T14 · Audit-alert wiring. Turns the INV1 tripwire into a RUNTIME detector: a
+ * `cross-tenant-attempt` audit event fires an operator alert immediately (EXPLORE §4e HIGH). Alert
+ * payload carries metadata only (no terminal bytes, INV10).
+ */
+import type { AuditEvent } from '../types.js'
+
+export type AlertKind = 'cross-tenant' | 'revocation' | 'auth-anomaly'
+
+export interface Alerter {
+  fire(kind: AlertKind, e: AuditEvent): Promise<void>
+}
+
+/** Fires a `cross-tenant` alert on `action === 'cross-tenant-attempt'`; no-op otherwise. */
+export async function onAuditEvent(e: AuditEvent, alerter: Alerter): Promise<void> {
+  if (e.action === 'cross-tenant-attempt') {
+    await alerter.fire('cross-tenant', e)
+  }
+}

relay-auth/src/audit/log.ts

@@ -0,0 +1,43 @@
+/**
+ * T4 · Immutable, append-only, ZERO-payload audit log (INV10). Entries are metadata only —
+ * principal, host_id, action, ts, outcome, reason, salted remoteAddrHash. Terminal payload is
+ * structurally excluded (no field carries it; `assertZeroPayload` enforces it before every append).
+ */
+import type { AuditAction, AuditEvent, AuditOutcome, AuthenticatedPrincipal, AuditSink } from '../types.js'
+import { AuditEventSchema } from '../types.js'
+import { assertZeroPayload } from './redact.js'
+
+export interface BuildAuditArgs {
+  readonly action: AuditAction
+  readonly principal: AuthenticatedPrincipal | null
+  readonly hostId: string | null
+  readonly sessionId: string | null
+  readonly jti: string | null
+  readonly outcome: AuditOutcome
+  readonly reason: string
+  readonly remoteAddrHash: string
+  readonly now: number
+}
+
+export function buildAuditEvent(p: BuildAuditArgs): AuditEvent {
+  const event: AuditEvent = {
+    ts: new Date(p.now * 1000).toISOString(),
+    action: p.action,
+    principalId: p.principal?.principalId ?? '',
+    accountId: p.principal?.accountId ?? '',
+    hostId: p.hostId,
+    sessionId: p.sessionId,
+    jti: p.jti,
+    outcome: p.outcome,
+    reason: p.reason,
+    remoteAddrHash: p.remoteAddrHash,
+  }
+  AuditEventSchema.parse(event) // strict schema rejects any smuggled extra key (INV10)
+  return event
+}
+
+/** Append-only (never update/delete). Guarded by `assertZeroPayload` (INV10). */
+export async function audit(sink: AuditSink, e: AuditEvent): Promise<void> {
+  assertZeroPayload(e)
+  await sink.append(e)
+}

relay-auth/src/audit/redact.ts

@@ -0,0 +1,42 @@
+/**
+ * T4 · INV10 zero-payload guard. Audit events are metadata ONLY; no field may carry terminal
+ * keystrokes/output. This rejects any string value that contains control/ESC bytes (a redraw
+ * sequence starts with `\x1b`) or exceeds a metadata length cap — a structural tripwire so a
+ * payload blob can never be smuggled through a `reason`/`hostId` field.
+ */
+import type { AuditEvent } from '../types.js'
+
+export const MAX_METADATA_LEN = 256 as const
+
+export class ZeroPayloadViolation extends Error {
+  constructor(message: string) {
+    super(message)
+    this.name = 'ZeroPayloadViolation'
+  }
+}
+
+/** Any C0 control char (incl. ESC \x1b), DEL, or C1 range → looks like terminal bytes. */
+const CONTROL_CHARS = /[\u0000-\u001F\u007F-\u009F]/
+
+function checkField(name: string, value: string): void {
+  if (value.length > MAX_METADATA_LEN) {
+    throw new ZeroPayloadViolation(`audit field '${name}' exceeds ${MAX_METADATA_LEN} chars`)
+  }
+  if (CONTROL_CHARS.test(value)) {
+    throw new ZeroPayloadViolation(`audit field '${name}' contains control/ESC bytes`)
+  }
+}
+
+/** Throws if any value looks like terminal bytes (INV10). */
+export function assertZeroPayload(e: AuditEvent): void {
+  checkField('ts', e.ts)
+  checkField('action', e.action)
+  checkField('principalId', e.principalId)
+  checkField('accountId', e.accountId)
+  checkField('outcome', e.outcome)
+  checkField('reason', e.reason)
+  checkField('remoteAddrHash', e.remoteAddrHash)
+  if (e.hostId !== null) checkField('hostId', e.hostId)
+  if (e.sessionId !== null) checkField('sessionId', e.sessionId)
+  if (e.jti !== null) checkField('jti', e.jti)
+}