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.

term-relay/mux/frame-guards.ts

@@ -0,0 +1,22 @@
+/**
+ * T2 · Boundary Zod validation of control-frame payloads (OPEN / WINDOW_UPDATE / GOAWAY).
+ *
+ * The decode+validate functions live in `relay-contracts` (they CBOR/int-decode then Zod-guard,
+ * throwing `ContractDecodeError` on a bad shape — never a partial value, INV boundary validation).
+ * P1 re-exports them plus a small `assertWithinFrameCeiling` helper the mux session uses to reject
+ * an oversized `payloadLen` before allocating (kills the OOM footgun, T6 frame-ceiling case).
+ *
+ * Security: NEVER validates DATA content (INV2) — DATA is opaque bytes.
+ */
+import { ContractDecodeError } from 'relay-contracts'
+
+export { decodeOpen, decodeWindowUpdate, decodeGoaway } from 'relay-contracts'
+
+/** Throw if a decoded `payloadLen` exceeds the configured ceiling (caller RSTs the stream). */
+export function assertWithinFrameCeiling(payloadLen: number, maxFrameBytes: number): void {
+  if (payloadLen > maxFrameBytes) {
+    throw new ContractDecodeError(
+      `frame payloadLen ${payloadLen} exceeds ceiling ${maxFrameBytes}`,
+    )
+  }
+}