Mapping Legal Instability: Retrieval-Based Detection of Adjudicative Interference Zones

The promise of equal treatment under law fractures whenever a court rules on materially identical facts in opposite ways. Aggregate disparity statistics register the breakage but cannot tell us when, where, or to whom it happens. We introduce adjudicative interference zones: regions of a legal corpus where materially comparable cases get routed through different procedural, evidentiary, or doctrinal gates and emerge with opposite outcomes. A facts-only retrieval pipeline detects them at scale by embedding the factual sections of public rulings and flagging high-similarity pairs whose operative dispositions diverge. Applied to 40,002 rulings from a Mexican federal administrative court (TFJA), the pipeline surfaces 6,613 candidates and a cleaned catalogue of 229 contradiction pairs across 112 connected components, each pair audited blind and stress-tested against a hostile second adjudicator. The catalogue resolves into structure rather than noise. At the outcome level, 61% are merits-access contradictions where one ruling adjudicates and a matched ruling sustains a plaintiff-side procedural bar, and 39% are merits-outcome contradictions where both panels clear the procedural threshold but disagree on the substance. At the mechanism level, 57% are procedural-gatekeeping splits and 29% are evidentiary-burden splits, the two regimes' dominant failure modes. Each zone is a concrete, inspectable failure of label consistency in a legal corpus, with direct consequences for facts-only outcome classifiers that ordinary held-out test sets cannot diagnose.