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/backoff.test.ts

@@ -0,0 +1,62 @@
+import { describe, expect, it, vi } from 'vitest'
+import { createBackoff, reconnectLoop, BACKOFF_CAP_MS } from '../src/transport/backoff.js'
+import type { Tunnel } from '../src/transport/tunnel.js'
+
+describe('createBackoff (T10)', () => {
+  it('follows 1s,2s,4s…cap 30s', () => {
+    const b = createBackoff()
+    const seq = [b.nextDelayMs(), b.nextDelayMs(), b.nextDelayMs(), b.nextDelayMs(), b.nextDelayMs(), b.nextDelayMs(), b.nextDelayMs()]
+    expect(seq).toEqual([1000, 2000, 4000, 8000, 16000, 30000, 30000])
+    expect(BACKOFF_CAP_MS).toBe(30_000)
+  })
+
+  it('reset() returns to 1s', () => {
+    const b = createBackoff()
+    b.nextDelayMs()
+    b.nextDelayMs()
+    b.reset()
+    expect(b.nextDelayMs()).toBe(1000)
+  })
+
+  it('jitter stays within [0.5×, 1×]', () => {
+    const b = createBackoff({ jitter: true, rng: () => 0 })
+    expect(b.nextDelayMs()).toBe(500) // 1000 * 0.5
+    const b2 = createBackoff({ jitter: true, rng: () => 1 })
+    expect(b2.nextDelayMs()).toBe(1000) // 1000 * 1.0
+  })
+})
+
+describe('reconnectLoop (T10, INV12)', () => {
+  const fakeTunnel = {} as Tunnel
+
+  it('resolves on the first successful dial and resets backoff', async () => {
+    const dial = vi.fn().mockRejectedValueOnce(new Error('down')).mockResolvedValueOnce(fakeTunnel)
+    const backoff = createBackoff()
+    const reset = vi.spyOn(backoff, 'reset')
+    const sleeps: number[] = []
+    const result = await reconnectLoop(dial, backoff, () => false, async (ms) => {
+      sleeps.push(ms)
+    })
+    expect(result).toBe(fakeTunnel)
+    expect(sleeps).toEqual([1000])
+    expect(reset).toHaveBeenCalled()
+  })
+
+  it('a revoked host does not reconnect (INV12)', async () => {
+    const dial = vi.fn().mockResolvedValue(fakeTunnel)
+    const result = await reconnectLoop(dial, createBackoff(), () => true, async () => {})
+    expect(dial).not.toHaveBeenCalled()
+    expect(result).toBeNull()
+  })
+
+  it('stops retrying once revoked mid-loop', async () => {
+    let revoked = false
+    const dial = vi.fn(async () => {
+      revoked = true
+      throw new Error('down')
+    })
+    const result = await reconnectLoop(dial, createBackoff(), () => revoked, async () => {})
+    expect(result).toBeNull()
+    expect(dial).toHaveBeenCalledTimes(1)
+  })
+})