This is a submission for Weekend Challenge: Dog Days Edition TL;DR — A walker records the walk on their phone, the route is hashed in the browser, and a 147-byte attestation signed by the walker's own key lands on Solana devnet. The owner checks the trace they were handed against the chain, and the app tells a tampered route apart from a corrupted file. Move one GPS fix eleven metres and the hash changes completely. That's the whole product. What I Built My ...