worktree-remove
A deny rule: it refuses removing a worktree, which may hold another session's uncommitted work, and names what to run instead.
What it catches
Removing a worktree, which may hold another session's uncommitted work.
Why
A worktree is where another session may be working right now, and its uncommitted changes live nowhere else. Check it is clean first with git -C <path> status, and remove it only once you know what it holds.
Seeing it
A verdict names its rule in brackets, which is how you got here:
deny [worktree-remove]: ...
magus describe rule worktree-remove prints the same entry at a terminal, and
magus describe rules lists every rule this workspace enforces.