httpx client with injectable clock/sleep/rng for testability. Successful
responses cached under data/bgg_cache/ keyed by endpoint+params; 202
retries follow the spec schedule (2/5/10/30s, give up after 5); 429/503
get jittered exponential backoff; consecutive requests are spaced
rate_limit_seconds apart. Parsers (via defusedxml, per security hook)
cover search, thing (+stats/+versions), and collection, including the
Not Ranked and error-document cases.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>