You'll notice
Subagents from plugin-registered agent types can no longer be spawned as pane-based teammates
What
When Claude Code tries to spawn a subagent as a pane-based teammate (a teammate running in its own terminal pane), it now checks whether the requested agent type was registered at runtime by a plugin. If so, it refuses and throws an error instead of trying to open a pane, telling you to spawn that agent with a different tool or to use an in-process teammate instead.
Why
This prevents a broken or unsupported launch attempt for plugin-registered agent types in pane mode, and points you toward the alternatives that do work: another spawning tool or in-process teammates.