As agent skill libraries grow toward 100,000 entries, a hub has to decide which skills a given model has already internalized so it can retire them for that model. The prevailing rule compares a run with the skill against a run without it and retires when the gain is near zero, but the paper points out that gain is near zero both for a genuinely internalized skill and for a skill no model can use at all, which it calls uncovered. The alternative withholds the skill, scores the model on a task synthesized from it, and trusts a high unaided score only when another model gains from that skill. Applied to four models, the published gain rule removed over half of the uncovered skills; on SkillsBench, 28 of 31 retirements rested on probes no run passed in full, while retiring on the unaided score cost no detectable reward, with Cohen's kappa of 0.42 against 0.23 for the gain rule. The authors release 1,251 skills with tasks and item scores under four models. The limitation is that unaided verdicts differ across models, so a hub has to read them per model rather than trust one global retirement list.
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Two sparse-autoencoder analyses have resisted scaling: matching semantically similar features across layers, and compressing large feature circuits into interpretable supernodes. This paper argues both are the same underlying problem, estimating semantic distances between SAE features that sit on different activation manifolds. Its representation treats each feature not as a single decoder vector but as an activation-weighted distribution over the hidden states expressing it, projects those distributions into a shared reference space, and compares them with Wasserstein distance. The representation is proved invariant to activation rescaling and stable under perturbation, and recovers true matches under finite-sample margin conditions. Empirically it outperformed decoder-vector and LLM-based baselines and captured subtle functional distinctions between related features, and it compressed large feature circuits into interpretable supernodes automatically. The limitation is that this is interpretability tooling: the paper demonstrates better feature matching and circuit compression, not that downstream interpretability claims become more accurate.