Why do I see Model is not allowed and then no reply

If agents.defaults.models is set, it becomes the allowlist for /model and any session overrides. Choosing a model that isn’t in that list returns:
Model "provider/model" is not allowed. Use /model to list available models.
That error is returned instead of a normal reply. Fix: add the model to agents.defaults.models, remove the allowlist, or pick a model from /model list.