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-e2e/test/sequence.test.ts

@@ -0,0 +1,61 @@
+import { describe, expect, it } from 'vitest'
+import { ReplayError } from '../src/errors.js'
+import { SequenceGuard } from '../src/sequence.js'
+
+describe('T7 SequenceGuard (INV13)', () => {
+  it('send: next() yields 0,1,2… strictly increasing', () => {
+    const g = new SequenceGuard('send')
+    expect(g.next()).toBe(0n)
+    expect(g.next()).toBe(1n)
+    expect(g.next()).toBe(2n)
+  })
+
+  it('two guards never share state', () => {
+    const a = new SequenceGuard('send')
+    const b = new SequenceGuard('send')
+    a.next()
+    a.next()
+    expect(b.next()).toBe(0n)
+  })
+
+  it('recv: in-order 0,1,2 accepted; lastAccepted tracks', () => {
+    const g = new SequenceGuard('recv')
+    g.accept(0n)
+    g.accept(1n)
+    g.accept(2n)
+    expect(g.lastAccepted).toBe(2n)
+  })
+
+  it('recv: replay of an accepted seq → ReplayError', () => {
+    const g = new SequenceGuard('recv')
+    g.accept(0n)
+    expect(() => g.accept(0n)).toThrow(ReplayError)
+  })
+
+  it('recv: reorder / gap / rewind all → ReplayError', () => {
+    const g1 = new SequenceGuard('recv')
+    expect(() => g1.accept(2n)).toThrow(ReplayError) // gap from start
+    const g2 = new SequenceGuard('recv')
+    g2.accept(0n)
+    expect(() => g2.accept(2n)).toThrow(ReplayError) // reorder/gap
+    const g3 = new SequenceGuard('recv')
+    g3.accept(0n)
+    g3.accept(1n)
+    g3.accept(2n)
+    g3.accept(3n)
+    g3.accept(4n)
+    expect(() => g3.accept(3n)).toThrow(ReplayError) // rewind (5 then 4-style)
+  })
+
+  it('bigint boundary: accepts near-u64-max without float error', () => {
+    const g = new SequenceGuard('recv')
+    // seed just below the boundary by direct successor stepping is impractical; assert range guard.
+    expect(() => g.accept(-1n)).toThrow(ReplayError)
+    expect(() => g.accept(2n ** 64n)).toThrow(ReplayError)
+  })
+
+  it('role misuse is rejected', () => {
+    expect(() => new SequenceGuard('recv').next()).toThrow(ReplayError)
+    expect(() => new SequenceGuard('send').accept(0n)).toThrow(ReplayError)
+  })
+})