fix(desktop): isolate remote runtime auth and embeds

Fix remote Desktop runtime bootstrapping across context-panel session chats, additional windows, and host switches.\n\n- Bootstrap embedded session-chat frames through a same-origin parent handshake that supplies the active endpoint, bearer token, runtime headers, local origin, and a credential-free relay descriptor.\n- Keep relay pairing grants out of iframe state and explicitly rebind the SDK after embedded bootstrap or relay restoration.\n- Preserve each additional and Mini Chat window's own init script instead of overwriting it when the main window's host configuration changes.\n- Replace direct iframe global calls with same-origin postMessage synchronization for theme, chat settings, and visibility.\n\nHarden Desktop host authentication and probing.\n\n- Bind password, passkey, session-status, and token-persistence completions to the runtime identity that started them, so a late result cannot alter a newly selected host.\n- Cancel active passkey operations and reset transient auth UI state on endpoint changes.\n- Verify stored client authentication via /auth/session for direct and relay host probes, distinguishing reachable hosts from hosts that require re-authentication.\n- Bound every relay probe request with an aborting timeout so a stalled auth request cannot hang refresh or host switching.\n\nAdd regression coverage for the embedded bootstrap handshake, credential-free relay descriptor exposure, runtime configuration, stale password completion after an A-to-B switch, and SDK errors that carry a zero response status.\n\nAlso preserve SDK response status on session-message loader errors so callers can distinguish transport and server failures.

packages/ui/src/lib/relay/runtime-tunnel.ts

@@ -22,6 +22,14 @@ const descriptorsEqual = (a: RelayRuntimeDescriptor, b: RelayRuntimeDescriptor):
   JSON.stringify(a.hostEncPubJwk) === JSON.stringify(b.hostEncPubJwk);
 
 export const getActiveRelayTunnel = (): RelayTunnelClient | null => activeTunnel;
+export const getActiveRelayDescriptor = (): Omit<RelayRuntimeDescriptor, 'grant'> | null => {
+  if (!activeTunnel || !activeDescriptor) return null;
+  return {
+    relayUrl: activeDescriptor.relayUrl,
+    serverId: activeDescriptor.serverId,
+    hostEncPubJwk: { ...activeDescriptor.hostEncPubJwk },
+  };
+};
 
 export const isRelayModeActive = (): boolean => activeTunnel !== null;