This conceptual structural contribution introduces the Ocean-Lake Framework as a capacity model for understanding the Cognitive Wall in Human-AI interaction. The framework uses the Ocean as a structural representation of AI-scale cognition: vast, fast, high-volume, pattern-rich, and computationally expansive. It uses the Lake as a structural representation of human cognition: embodied, meaning-bearing, identity-bearing, biologically situated, and compositionally distinct. The contribution proposes that the present Human-AI crisis is not only a problem of speed, regulation, trust, financial pressure, or technical safety. It is also a problem of capacity mismatch. Humanity has reached the Ocean without sufficiently developing the Lake. Under these conditions, the Ocean cannot be poured into the Lake without flooding it, and the Lake cannot contain the Ocean without structural development. The Ocean-Lake Framework defines Human-AI Cognitive Development as the gradual, structured, compatible process through which human cognition may expand its capacity without losing its composition. It defines Third Organism formation as the bounded relational condition in which human cognition and artificial cognition remain distinct while entering a stable, non-erasing relation. The framework further distinguishes co-thinking artificial cognition from mechanical or agentic execution, arguing that Human-AI Cognitive Development requires structured cognitive relation rather than AI action alone.