ml::validation is gated behind validation-mod, but dqn/config.rs:177 references crate::validation::RegimeMetrics unconditionally. Both services pull in dqn::config via the trainer pipeline, so they need the gate opened to compile. Cheaper than refactoring 700+ refs. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>