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/src/service/install.ts

@@ -0,0 +1,78 @@
+/**
+ * Service install dispatcher — PLAN_RELAY_AGENT T17. Detects the platform, writes the unit, and
+ * loads it. REFUSES to install as root (EXPLORE §4d least privilege). All IO is injected so the
+ * logic is unit-testable without touching the real system.
+ */
+import type { AgentConfig } from '../config/agentConfig.js'
+import {
+  buildLaunchdPlist,
+  launchdLoadCommand,
+  launchdPlistPath,
+  launchdUnloadCommand,
+} from './launchd.js'
+import {
+  buildSystemdUnit,
+  systemdDisableCommand,
+  systemdEnableCommand,
+  systemdUnitPath,
+} from './systemd.js'
+
+export type ServicePlatform = 'launchd' | 'systemd'
+
+export class RootRefusedError extends Error {
+  constructor() {
+    super('refusing to install the agent service as root — run as the logged-in user (least privilege)')
+    this.name = 'RootRefusedError'
+  }
+}
+
+export interface InstallDeps {
+  writeFile(path: string, content: string): void
+  runCommand(cmd: string, args: readonly string[]): Promise<void>
+  getuid(): number
+  homedir(): string
+  username(): string
+  binPath(): string
+}
+
+/** Map a Node platform to its service manager, or null if unsupported. */
+export function detectPlatform(os: NodeJS.Platform): ServicePlatform | null {
+  if (os === 'darwin') return 'launchd'
+  if (os === 'linux') return 'systemd'
+  return null
+}
+
+/** Write + load the service unit for `platform`. Throws RootRefusedError if running as root. */
+export async function installService(
+  _cfg: AgentConfig,
+  platform: ServicePlatform,
+  deps: InstallDeps,
+): Promise<void> {
+  if (deps.getuid() === 0) throw new RootRefusedError()
+  const bin = deps.binPath()
+  if (platform === 'launchd') {
+    const path = launchdPlistPath(deps.homedir())
+    deps.writeFile(path, buildLaunchdPlist(bin))
+    const { cmd, args } = launchdLoadCommand(path)
+    await deps.runCommand(cmd, args)
+    return
+  }
+  const path = systemdUnitPath(deps.homedir())
+  deps.writeFile(path, buildSystemdUnit(bin, deps.username()))
+  const { cmd, args } = systemdEnableCommand()
+  await deps.runCommand(cmd, args)
+}
+
+/** Unload the service unit for `platform`. */
+export async function uninstallService(
+  platform: ServicePlatform,
+  deps: Pick<InstallDeps, 'runCommand' | 'homedir'>,
+): Promise<void> {
+  if (platform === 'launchd') {
+    const { cmd, args } = launchdUnloadCommand(launchdPlistPath(deps.homedir()))
+    await deps.runCommand(cmd, args)
+    return
+  }
+  const { cmd, args } = systemdDisableCommand()
+  await deps.runCommand(cmd, args)
+}