Vector-quantized motion tokenizers provide a compact discrete interface for text-to-motion generation, but most motion-code priors treat code indices as unordered categorical labels. This view overlooks a key property of motion codes: they are decoder-bound prototypes of physical movement, and their learned codebooks can carry meaningful local kinematic geometry. We verify this property through codebook diagnostics. Distances between learned PartVQ group-specific codes align with local motion-prototype distances, shuffled controls remove this alignment, and replacing codes with progressively farther neighbors induces monotonically larger decoded motion changes. These results show that motion codebooks exhibit measurable, non-random, and decoder-causal geometry. Based on this observation, we propose \textbf{MoGeFlow}, a text-to-motion model that generates through motion codebook geometry. MoGeFlow represents each motion-code frame as a structured set of PartVQ group-specific code embeddings, learns a text-conditioned continuous flow over these frame states, and projects terminal states back to valid motion codes for frozen decoding. This preserves the compactness and validity of discrete tokenization while replacing categorical code prediction with geometry-aware codebook-space generation. Experiments set new state of the art in R-Precision on HumanML3D and KIT-ML, achieve the best HumanML3D MultiModal Distance and KIT-ML FID among generated methods, and obtain the best MotionMillion R@1, R@2, R@3, and FID under the benchmark protocol.

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