C3R Controls Cross-Domain Contamination in Multi-Domain Retrieval

Retrieval systems operating over mixed-domain corpora often return relevant but domain-inappropriate evidence, a problem that standard ranking metrics and conformal risk control methods struggle to address effectively. This issue can lead to under-coverage in critical domains. A novel control layer called C3R (Certified Domain Consistency for Multi-Domain Retrieval) has been introduced to tackle this. C3R provides a certified per-domain contamination budget without requiring query-time labels. It employs a two-split scheme based on risk-controlling prediction sets, offering finite-sample transfer bounds and supporting heterogeneous budgets. The method guarantees a reduction in wrong-domain evidence, particularly in the hardest domains, and maintains higher recall than strong calibrated cascades at equivalent certified contamination levels. Its effectiveness has been replicated across multiple testbeds, including federal regulations, and an LLM-judged probe indicates that C3R reduces wrong-authority grounding.