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-web/src/host-pin-store.ts

@@ -0,0 +1,57 @@
+/**
+ * T8 (v0.10) — `HostPinStore`: a CACHE / AUDIT TRAIL of the API-sourced host fingerprint per
+ * `host_id`, NOT an independent trust root.
+ *
+ * It never establishes trust from a relay-forwarded handshake — `record` only ever stores a value
+ * the caller already verified against the authenticated `HostRecord.enrollFpr` (§4.2, fetched
+ * out-of-band of the relay over the P5-authenticated HTTPS API). Drift between a freshly-sourced
+ * API fingerprint and the cached one is surfaced for review, but the API value is authoritative.
+ *
+ * Only the PUBLIC fingerprint (`enroll_fpr`) is persisted — never a key, secret, or plaintext
+ * (INV5/INV9): a fingerprint is safe at rest and is exactly what enables first-connect MITM defense.
+ */
+
+const KEY_PREFIX = 'relay-web:hostpin:'
+
+export interface HostPinStore {
+  /** last cached API-sourced enroll_fpr for this host, or null if none cached yet */
+  get(hostId: string): string | null
+  /** cache an API-VERIFIED fingerprint (audit/drift detection) — caller must have verified it */
+  record(hostId: string, apiSourcedFpr: string): void
+}
+
+/**
+ * In-memory fallback for non-DOM/test contexts (keeps the store usable everywhere). The store only
+ * ever calls `getItem`/`setItem`, so only those are implemented (cast to the Storage interface).
+ */
+function memoryStorage(): Storage {
+  const map = new Map<string, string>()
+  return {
+    getItem: (k: string) => map.get(k) ?? null,
+    setItem: (k: string, v: string) => {
+      map.set(k, v)
+    },
+  } as unknown as Storage
+}
+
+function defaultStorage(): Storage {
+  try {
+    if (typeof localStorage !== 'undefined') return localStorage
+  } catch {
+    // localStorage can throw in sandboxed contexts; fall back to memory.
+  }
+  return memoryStorage()
+}
+
+export function createHostPinStore(storage: Storage = defaultStorage()): HostPinStore {
+  const keyFor = (hostId: string): string => `${KEY_PREFIX}${hostId}`
+  return {
+    get(hostId: string): string | null {
+      return storage.getItem(keyFor(hostId))
+    },
+    record(hostId: string, apiSourcedFpr: string): void {
+      // Store only the API-verified value; this method never derives trust from a handshake.
+      storage.setItem(keyFor(hostId), apiSourcedFpr)
+    },
+  }
+}