# M01-L04 — Lab contract

**Build:** Mine toy blocks at two difficulties and verify target.

**Pass:** Mined blocks pass; mutated nonce fails; harder target needs more trials on average.

**Failure injection:** Comparing only block counts ignores accumulated work.

**Review question:** Why is this toy PoW not real network consensus?

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