Function tree_try_move 

pub fn tree_try_move(
    node: RNode,
    token: u64,
    parent: Option<u64>,
    index: Option<usize>,
) -> Result<(), &'static str>

Programmatically move a tree row through the same guard → commit path a native drag takes (docs/tree.md): consult the piece’s guards, defer the app’s on_move, and tell the native host to re-query. This is how the dayscript tree_move: step and the mock probe drive moves without a native gesture. Call with no borrow held.