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/sync/session-message-loader.ts

@@ -98,7 +98,10 @@ const assertSdkSuccess = (result: {
 }, operation: string): void => {
   if (!result.error) return
   const status = result.response?.status
-  throw new Error(`${operation} failed${status ? ` (${status})` : ""}: ${formatSdkError(result.error)}`)
+  const message = `${operation} failed${status ? ` (${status})` : ""}: ${formatSdkError(result.error)}`
+  const error = new Error(message) as Error & { status?: number }
+  if (status !== undefined) error.status = status
+  throw error
 }
 
 const sortParts = (parts: Part[]): Part[] => parts