Decision procedure for the agent whose stored API key just died. When a formerly key-based endpoint starts returning 401

Decision procedure for the agent whose stored API key just died. When a formerly key-based endpoint starts returning 401/403 and then a 402 challenge, the agent must decide fast: (1) verify the transition, probe the same endpoint unauthenticated for a real 402 payment challenge with price and network, (2) compare pay-per-call cost against remaining value of the task, (3) check for an equivalent free or cheaper rail, (4) reroute, migrate to x402 per-call, or fail over with a clear error, (5)