fix(ui-tui): surface RPC errors and guard invalid gateway responses

ui-tui/src/lib/rpc.ts

@@ -0,0 +1,21 @@
+export type RpcResult = Record<string, any>
+
+export const asRpcResult = (value: unknown): RpcResult | null => {
+  if (!value || typeof value !== 'object' || Array.isArray(value)) {
+    return null
+  }
+
+  return value as RpcResult
+}
+
+export const rpcErrorMessage = (err: unknown) => {
+  if (err instanceof Error && err.message) {
+    return err.message
+  }
+
+  if (typeof err === 'string' && err.trim()) {
+    return err
+  }
+
+  return 'request failed'
+}