Phone validation API results need distinct handling for valid, unknown and failed checks

A signup form that treats every phone-check result as pass or reject can wrongly block users during outages or on unanswerable questions. The article presents a dependency-free Python fixture with four branches (normal, unknown, provider_failure, otp) that returns fixed outputs for testing signup logic without credentials or network calls. The free Basic Lookup route does not return line type, ownership, reachability or OTP delivery, so the design must not rely on those fields. The proposed design maps valid results to continuation under the team's own policy, unknown results to review or an existing OTP step, and provider failures to bounded retries before review. Questions the route cannot answer are handed off to a separate OTP provider the team already operates.