Port to Rust

A port is a behaviour-preserving move, and nothing else

The one rule this skill exists to enforce: during a port, behaviour changes and code improvements are separate commits, separate reviews, and preferably separate weeks. A port that also fixes bugs cannot be validated — every difference is ambiguous between the fix and the regression, and the differential harness reports both identically. Improvements are written down as a follow-up list and shipped after parity is proven.

Start from the parity contract, not from the code