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/originConfig.test.ts

@@ -0,0 +1,43 @@
+import { describe, expect, it } from 'vitest'
+import { ensureAllowedOrigin, subdomainOrigin, type OriginFsDeps } from '../src/service/originConfig.js'
+
+function memFs(initial: string | null): { fs: OriginFsDeps; get(): string } {
+  const store = { content: initial }
+  const fs: OriginFsDeps = {
+    exists: () => store.content !== null,
+    read: () => store.content ?? '',
+    write: (_p, c) => {
+      store.content = c
+    },
+  }
+  return { fs, get: () => store.content ?? '' }
+}
+
+const PATH = '/etc/web-terminal.env'
+
+describe('ensureAllowedOrigin (T17, EXPLORE §3)', () => {
+  it('composes https://<subdomain>.term.<domain>', () => {
+    expect(subdomainOrigin('host-42', 'example.com')).toBe('https://host-42.term.example.com')
+  })
+
+  it('appends the origin when the file has none', () => {
+    const { fs, get } = memFs('PORT=3000\n')
+    ensureAllowedOrigin(PATH, 'host-42', 'example.com', fs)
+    expect(get()).toContain('ALLOWED_ORIGINS=https://host-42.term.example.com')
+    expect(get()).toContain('PORT=3000')
+  })
+
+  it('is idempotent (no duplicate on a second run)', () => {
+    const { fs, get } = memFs('ALLOWED_ORIGINS=https://host-42.term.example.com\n')
+    ensureAllowedOrigin(PATH, 'host-42', 'example.com', fs)
+    const matches = get().match(/host-42\.term\.example\.com/g) ?? []
+    expect(matches).toHaveLength(1)
+  })
+
+  it('preserves existing origins (never weakens the Origin check)', () => {
+    const { fs, get } = memFs('ALLOWED_ORIGINS=https://existing.example.com\n')
+    ensureAllowedOrigin(PATH, 'host-42', 'example.com', fs)
+    expect(get()).toContain('https://existing.example.com')
+    expect(get()).toContain('https://host-42.term.example.com')
+  })
+})