Correct Action Timing Is Not Action Fidelity in World Models

World models used for planning must predict how changing an action changes the future. Under non-anticipation and a nonzero response moment, we prove that an external randomized code identifies action timing from its rightmost nonzero code-transition moment. Even with exact timing, a restricted predictor at the population-risk optimum can estimate action effects less accurately than predicting no effect. An exact paired-risk identity gives an architecture-independent sufficient prediction-accuracy condition at the action-effect scale. Controlled visual experiments recover all 18 offset families, while only 7 of 36 aligned models beat zero response after 12 epochs. This distinction persists with longer controlled training and larger models on public Walker/Walk. Response weighting, motivated by the identity, improves eleven of twelve controlled comparisons and both Walker architectures under matched labels.