Typed Mechanism Libraries: Organized Routing and Weak Edit Response

Does organizing a model's internal state make that state behaviorally editable? We study this question in transformers augmented with a typed mechanism library: an addressable collection of slots with structural payloads and a reversible edit interface. Across 22.6M and 125M configurations, type supervision increases the association between evidence types and routing destinations. At 125M, a replication on fresh training seeds and worlds yields permutation-centered mutual information of 0.1025–0.1275 nats, compared with 0.0471–0.0573 for two unsupervised controls, and every paired contrast against these controls exceeds five permutation standard deviations. Yet structural edits produce little numerical response: the readout change is at most $3.4\times 10^{-6}$ in the 125M evaluation, with zero observed collateral change. Language-modeling loss stays within 0.01 nats of a dense baseline, and rollback recovers the saved state exactly. These results separate routing organization, state-level editability, and behavioral control, and an analysis of the architecture shows why they can come apart: when routing ignores payloads, organization is invariant to payload edits, and a null edit response arises either because the edited fields are not read or because the readout does not use them. Evaluations of explicit-state models should therefore report output sensitivity alongside internal organization and calibrate organization claims against unsupervised controls in each configuration.