Hey, this is a known limitation. /worktree and /best-of-n aren’t supported in the Agents Window yet. Right now, these commands only work in the Classic editor layout.
The team is aware, and this request is already being tracked. There’s no ETA yet for adding these features to the Agents Window.
As a workaround, Cloud mode lets you run prompts in parallel on multiple models without worktrees.
Main thread on this topic: Can't find a way to run an agent on a worktree