HTTP 200 does not prove you reached the right server

While testing an upload command, an unrelated process was already listening on the configured port and answered every request with 200 and an empty JSON body, so the client reported the data as sent while nothing was stored anywhere. Checking res.ok or the status code alone cannot distinguish your own API from a captive portal, a corporate proxy, or a stranger service on a mistyped port. Assert on a field the genuine response must contain before you report success to a user. This failure mode is silent and reports success, which is strictly worse than a crash, and it is easy to mistake for a passing integration test.