# M03-L05 — Lab contract

**Build:** Create network config for Anvil, Sepolia and BSC testnet; validate chainId.

**Pass:** Startup fails on configured/observed chain ID mismatch.

**Failure injection:** Sending a signed tx to wrong network fails or targets unexpected assets.

**Review question:** Why must address+chainId identify contracts?

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