kiosk-pow-cuckoo is an optional Cuckatoo-Cycle (Cuckoo Cycle variant) proof-of-work backend for the Kiosk framework. Ships the provider-side Ruby VERIFIER only. The verifier is cheap (a handful of hash evaluations; no wall-clock figure is benchmarked), security-critical, and validated against Grin's Cuckatoo29 CI test vector. A reference Python solver (solve_cuckoo.py) ships alongside for parity testing; production solving is the client's concern. The implementation is clean-room from Tromp's public-domain algorithm spec (doc/spec, doc/mathspec) — no GPL/FAIR-MINING code is included. BLAKE2b-256 comes from kiosk-pow, the base of every Kiosk PoW backend. SipHash-2-4 is pure Ruby from the public-domain SipHash spec with Cuckatoo's non-standard initialization (keys feed directly into v0..v3 without XOR-ing the 0x736f6d65... magic constants). Does not depend on kiosk-core or Rails — pure Ruby, no native extensions.