Two colleagues disagree: one wants to always retrieve b...

Building a confidence-gated router is an expensive and unsolved problem, as it requires highly reliable uncertainty estimates. Given the one-month constraint, you should reject this binary choice and focus on reranking-to-front and ranked-list truncation. These techniques directly address the root cause of the failure—the ‘trough’ in the context window—at a fraction of the engineering cost.

Evidence that would flip this recommendation would be a finding that truncation alone cannot pull the worst-position accuracy above the closed-book baseline (A0). If truncation fails to close this gap, then the complexity of building a router becomes a necessary investment.