The Cost Architecture of Cognition

Diagnostic categories for neurodivergence treat conditions as discrete kinds distinguished by symptom inventories. This paper rejects that ontology. Neurocognitive variation is characteristic regions in a continuous parameter space whose primitives are the costs, thresholds, gains, and decay-rates of a small set of cognitive operations. Two parameters, compression rate and closure stability, double-dissociate the autistic and ADHD phenotypes; their combination produces the AuDHD presentation as a parameter conflict, not a sum of symptoms. The framework is derived from mechanism and predicts phenomenology forward. The diagnostic manual is a validation floor, not ground truth, and the contribution lies in the regions the parameter space occupies that the nosology does not name and the categories it shows to be mis-sealed. We position the account at Marr's computational level and advance it as a strong hypothesis with explicit falsification conditions, claiming the engagement-and-attention slice of these conditions.