What
A guard was added before Claude Code runs any host-provided $.* call originating from a plugin or hooks module. The call is now refused if the caller chain or its environment ID is still marked as not yet admitted, since plugin.register runs once per admitted set of plugins and a call from an unadmitted hooks module means that module isn't part of the built set yet.
Why
This prevents a plugin's hooks module from making host calls before it has actually been admitted into the running set, closing a window where such a call could otherwise slip through.
Names in the bundleplugin.register
Documented inclaude-code/plugins/mods/admin
The entry above is what we published on the day. These lines were added later, as Anthropic's own pages caught up, and they sit beside the original rather than replacing it.
Confirmed since
Anthropic's documentation has since written up plugin.register, on Manage mods for your organization.
Each time another mod is about to load, your mod receives the list that `claude plugin validate` prints, in an event named [`plugin.register`](/docs/en/plugins/mods/reference#other-mods). A mod in `prependPlugins` can read that list and re…plugins/mods/admin see the edit
One source agreesOne thing we can check says the same as this entry.
Anthropic's documentation agrees
Anthropic's documentation has since written up plugin.register, on Manage mods for your organization.