Availability interfaces and request protection

An availability read is evidence of an offer, not a carrier reservation.

The public contract

AvailabilityCarrier::available receives an 11-character national UK 01/02 range made of digits and underscores, with size 20. Its result contains http_code, body and curl_errno. A successful body is a JSON list of number strings. Allocation does not belong in this method.

Bound the transport

Use verified TLS, bounded response sizes, explicit deadlines and no unsafe redirects or automatic retries. The optional supplied transport uses a 5-second connect timeout, a 12-second total timeout and a 256 KiB response cap. Equivalent protection is required for other carriers.

Share the limiter

The reference holds one shared lock through each call, with five seconds between starts and a 15-second bound on queue and spacing waits. Per-session attempts are limited to 30 in 60 seconds. Every availability consumer sharing carrier authority must participate. Separate local files on separate hosts are not a distributed limiter.