# M01-L03 — Lab contract

**Build:** Build 5-leaf tree, generate inclusion proof for leaf 3 and verify.

**Pass:** Valid proof passes; modified leaf or sibling fails.

**Failure injection:** A forged or wrongly ordered sibling can produce an invalid proof.

**Review question:** How does proof size scale with transactions?

Status: specification; only count as executable when source and tests are present and verified.