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Plugins can now open UI panels, capped per plugin, with a hook that can veto closing one
What
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.
Why
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.
Names in the bundleui.close