Audit any eval, metric, experiment, or benchmark for leakage — does external ground-truth enter independently, or are the model, scorer, and designer just confirming a result no outside truth ever produced? Use before trusting any 'how we'll know it worked' — an A/B, a holdout, a score, a validation

Audit a validation for leakage: does outside ground truth actually enter, or is everyone confirming a result no one independently produced? Goal The name is the Mandela Effect — a whole population confidently remembers something that never independently happened; a leaky validation is the same shape. Walk the 8 patterns below. mandela checks one thing: whether a validation is independent, or whether the designer, model, and scorer are only confirming each other. Workflow 1. Identify the validation (eval / metric / experiment / holdout / "how we'll know"). Name its components — what plays model, scorer, designer, dataset. 2. Ask the core question : does external ground truth enter independently ? 3. Test the validation against all 8 patterns below (some apply only to certain components — a human subject, a scorer); report only the ones that fire, each by name. 4. Give the independent ground truth fix for each hit. The 8 leakage patterns 1. Recall, not reason — a memorized answer recited instead of one actually derived; the system already knows the result it is supposedly computing. 2. Wrong null hypothesis — an ablation that removes a surface label but not the underlying signal the system actually exploits, so the "control" still leaks. 3. Shared hallucination — two components verifying each other; circularity reported as a number. 4. Tautology — a scorer grading buckets it drew itself. 5. Verifier = designer — a private, unreproducible recipe in a holdout's clothes. 6. Shared pool bias — train and holdout drawn from one labeler pool, so one bias enters both sides. 7. Frame injection — a question that hands the subject the hypothesis. 8. Demand characteristics — measured subjects who know they're being measured. Rules Subtlety that bites twice: you can blind the output value and still leak the collection recipe . Read only — name the leak and the independence fix; don't rewrite the experiment. For a high stakes validation, you may add one independent fresh context auditor ( N=1 ) handed only the validation design, not this session's reasoning, to re run the 8 pattern taxonomy blind; the default remains same session and read only. Verification Turn mandela on this audit: 1. Run patterns 3– 5 on yourself: are you a scorer grading buckets you drew (Tautology, 4)? is the verifier the designer ( 5)? is your verdict a shared hallucination with the design's own claims ( 3)? 2. Could a reader who didn't run the audit reach your verdict from the cited evidence alone — independent ground truth? 3. The report names the root, not a laundry list.