# M08-L01 — Lab contract

**Build:** Compute x*y=k swap output including fee and price impact.

**Pass:** Output positive and less than reserve; invariant nondecreasing after fee.

**Failure injection:** Using spot price without slippage limits invites poor execution.

**Review question:** Why does large trade cause price impact?

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