Claude Code has a new system for managing UI panels ('panes') that plugins can open, each tracked by an id, title, owning plugin, and focus state. A single plugin can only have a limited number of panes open at once; opening another beyond that limit requires closing one first. Closing a pane now runs an asynchronous ui.close hook chain first, so a hook can intervene and keep the pane open instead of letting it close.
This gives plugins a structured way to present multiple panels while preventing any one plugin from opening an unlimited number of them, and lets hooks control cleanup behavior when a pane is about to close.
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.
* **`$`**: the test's own `$`, which acts as Claude Code. It isn't the [mods API](/docs/en/plugins/mods/reference#mods-api-methods) that a hook receives. Each of its methods fires the event of the same name, sends it through your mod's hoo…plugins/mods/test see the edit
Anthropic's documentation has since written up ui.close, on Test a mod.