Struct TreeMovesDriver 

pub struct TreeMovesDriver {
    pub can_move: Box<dyn Fn(u64, Option<u64>, Option<usize>) -> MoveVerdict>,
    pub moved: Box<dyn Fn(u64, Option<u64>, Option<usize>)>,
}

The move closures the tree() piece supplies (docs/tree.md). Exposed to the backend as day_spec::TreeMoves by the tree source adapter; also driven directly by tree_try_move (the dayscript tree_move: step and the mock probe).

Fields

can_move: Box<dyn Fn(u64, Option<u64>, Option<usize>) -> MoveVerdict>

Consult the guards (structural + the app’s): may token land under parent at index? index: None = dropped onto the parent (append).

moved: Box<dyn Fn(u64, Option<u64>, Option<usize>)>

Commit an accepted move: defers the app’s on_move through the event queue (day_spec::Event::TreeMove); the app’s own data write drives the reload.