# M03-L01 — Lab contract

**Build:** Call eth_chainId, eth_blockNumber, eth_getBlockByNumber on Anvil.

**Pass:** Returned chain ID and block height match local node.

**Failure injection:** Treating one RPC response as authoritative creates stale reads.

**Review question:** How do you detect provider lag?

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