feat: add private relay for end-to-end-encrypted remote access (#2087)

Adds OpenChamber Relay — an opt-in way to reach an instance from a phone,
browser, or another desktop from anywhere, with no open inbound ports, no
tunnel, and no shared LAN. The instance dials outbound to a relay; all app
traffic (HTTP, the event stream, terminal, dictation) is multiplexed and
encrypted through a single connection per client, so the relay only ever
forwards opaque ciphertext.

Transport
- End-to-end-encrypted channel over WebCrypto (ECDH P-256 -> HKDF ->
  AES-256-GCM) with a capability-negotiated handshake and a small
  HTTP/SSE/WebSocket multiplexing protocol. A byte-compatible JS host mirror
  is cross-checked by tests.
- Host: outbound connection manager, per-client tunnel dispatcher to the local
  server over loopback, reuse of the existing instance identity key, and
  management routes. Disabled by default; explicit opt-in.
- Client: plugs into the existing runtime layer (runtime-fetch/-url/-switch/
  -auth, event pipeline, terminal, dictation) so features work over the relay
  unchanged; direct-URL and Electron realtime-proxy paths are untouched.

Pairing & UX
- Relay section in Settings -> Remote Instances (live status, QR/link pairing,
  revocation via the existing client-token list) and the mobile connect flow.
- Frame batching and idle-gated keepalive keep tunnel message volume low
  without affecting streaming smoothness.

Security
- The tunnel is transport only; the server authenticates every tunneled
  request exactly as for a direct remote client.
  fragments only. The relay stores no keys, tokens, or payloads.

Operability
- The endpoint can be pinned to a self-hosted rel
  paired clients inherit it from the offer automatically.
- Relay module DOCUMENTATION.md and a relay-trans
  invariants that future WebSocket/streaming changes must follow.

The relay transport is complete and tested; the UI for enabling and pairing
is gated behind openchamber_relay_gate and stays

packages/web/server/index.js

@@ -89,6 +89,7 @@ import { createProjectConfigRuntime } from './lib/projects/project-config.js';
 import { createRemoteClientAuthRuntime } from './lib/client-auth/remote-clients.js';
 import { createPreviewProxyRuntime } from './lib/preview/proxy-runtime.js';
 import { attachRealtimeProxy } from './lib/realtime-proxy.js';
+import { createRelayService } from './lib/relay/service.js';
 import { createProxyMiddleware, responseInterceptor } from 'http-proxy-middleware';
 import webPush from 'web-push';
 
@@ -1286,6 +1287,19 @@ async function main(options = {}) {
   const tunnelRuntimeContext = tunnelWiringRuntime.initialize(app, port);
   const { tunnelService, startTunnelWithNormalizedRequest } = tunnelRuntimeContext;
 
+  // Private relay host service: config + management routes + host client
+  // lifecycle. Loopback port comes from the same source the tunnel uses so
+  // relay-tunneled requests hit the local Express app on 127.0.0.1.
+  const relayService = createRelayService({
+    crypto,
+    os,
+    readSettingsFromDiskMigrated,
+    writeSettingsToDisk,
+    remoteClientAuthRuntime,
+    getLocalPort: () => tunnelRuntimeContext.getActivePort(),
+  });
+  relayService.registerRoutes(app);
+
   await featureRoutesRuntime.registerRoutes(app, {
     crypto,
     fs,
@@ -1395,6 +1409,9 @@ async function main(options = {}) {
     console.warn('[ScheduledTasks] Failed to start runtime:', error?.message || error);
   }
 
+  // Only opens a relay control socket when the user opted in (config enabled).
+  void relayService.startIfEnabled();
+
   return {
     expressApp: app,
     httpServer: server,
@@ -1425,6 +1442,11 @@ async function main(options = {}) {
     },
     stop: (shutdownOptions = {}) => {
       realtimeProxyRuntime.stop();
+      try {
+        relayService.stop();
+      } catch {
+        // best-effort teardown of the relay host client
+      }
       try {
         dictationRuntime?.stop?.();
       } catch {