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

ui-tui/src/__tests__/rpc.test.ts

@@ -0,0 +1,27 @@
+import { describe, expect, it } from 'vitest'
+
+import { asRpcResult, rpcErrorMessage } from '../lib/rpc.js'
+
+describe('asRpcResult', () => {
+  it('keeps plain object payloads', () => {
+    expect(asRpcResult({ ok: true, value: 'x' })).toEqual({ ok: true, value: 'x' })
+  })
+
+  it('rejects missing or non-object payloads', () => {
+    expect(asRpcResult(undefined)).toBeNull()
+    expect(asRpcResult(null)).toBeNull()
+    expect(asRpcResult('oops')).toBeNull()
+    expect(asRpcResult(['bad'])).toBeNull()
+  })
+})
+
+describe('rpcErrorMessage', () => {
+  it('prefers Error messages', () => {
+    expect(rpcErrorMessage(new Error('boom'))).toBe('boom')
+  })
+
+  it('falls back for unknown errors', () => {
+    expect(rpcErrorMessage('broken')).toBe('broken')
+    expect(rpcErrorMessage({ code: 500 })).toBe('request failed')
+  })
+})