Verification has to reject forgeries - a wrong leaf or a tampered sibling must not recompute the root. Today you pin those failures.
Show that a wrong leaf or an altered sibling makes VerifyProof return false.
A proof system that only ever says “yes” is worthless; the value is that it says “no”
to anything false. Swap in a leaf that is not there (mallory) and the fold starts
from a different leaf hash, so the recomputed root misses. Keep the right leaf but
nudge a single sibling hash by one bit (0x6bfe63ee to 0x6bfe63ef) and the very
first HashNode diverges, cascading to a wrong root.
There is no way to patch up a bad input partway - the hash of the leaf and every sibling all funnel into one root, so a single wrong ingredient anywhere breaks the match. That is the tamper-evidence of a Merkle proof: an attacker who wants a forged proof to verify would need to find a hash collision, which a real cryptographic hash makes infeasible.
ok1 := VerifyProof(0xfd610c23, []byte("mallory"), proof0) // falsebad := []ProofStep{{0x6bfe63ef, true}, {0x1cde9a86, true}}ok2 := VerifyProof(0xfd610c23, []byte("alice"), bad) // false