We introduce cognitosymbiosis as a formal framework for human–large reasoning model (LRM) cognitive partnership and propose the Cognitive Emergent Evolutionary Potential (CEEP) construct as its central theoretical contribution. Cognitosymbiosis describes an obligate mutualism in which human semantic intelligence and LRM high-dimensional geometric intelligence combine to produce capabilities that are emergent rather than additive — access to cognitive regions that neither system can navigate alone. We ground this claim mechanistically: LRMs operate in embedding spaces of thousands to tens of thousands of dimensions, performing geometric operations (rotations, projections, similarity computations) that are computationally inaccessible to unaided human cognition; humans provide the semantic anchors, meaning-saturated constraints, and evaluative frameworks that make this geometric navigation humanly significant. The partnership thus expands the humanly accessible frontier of high-dimensional geometric intelligence. The CEEP framework parallels the Evolutionary Emergent Potential (EEP) construct previously introduced by Levinson (2019), which drew on slipped-strand mispairing (Levinson & Gutman, 1987) to explain how iterated molecular variation generates evolutionary novelty. As EEP describes the generation of variation that selection can act upon in biological evolution, CEEP describes the generation of cognitive variation — the exploration of high-dimensional conceptual space — that human judgment selects and directs toward meaningful outcomes. This parallel is extended by Margulis's endosymbiosis: as mitochondrial engulfment produced a genuinely new cellular entity with capabilities neither partner possessed alone, cognitosymbiosis produces a genuinely new cognitive entity with access to frontiers unavailable to either human or LRM operating independently. We present six testable predictions, distinguish CEEP from two alternative accounts, characterize memory, persistence, and compounding CEEP dynamics, address the self-instantiating recursive property of this research program, and conclude with governance implications: specifically, that realizing the benefits of cognitosymbiosis at scale requires institutional structures that treat human expertise as a common-good contribution rather than a labor commodity subject to market displacement.