Taku Build - Auditable Implementation

Build implements the approved contract and leaves Review enough evidence to decide whether the work can ship.

Rule labels: [IRON LAW] means a non-negotiable correctness constraint. [GUIDANCE] means a strong default that may adapt when context justifies it.

[IRON LAW] No production code without a failing test, reproduction, or explicit verification anchor first. If the repo lacks a test harness, create the smallest reproducible check and say why.