cleanup

kiln-core/src/board.rs

@@ -235,11 +235,13 @@ impl Board {
         self.solid_at(x, y).is_none()
     }
 
-    /// Returns `true` if the mover as `(x1, y1)` can enter `(x2, y2)` — i.e. it would not
-    /// break the rules of "one solid per cell, except for player + grab".
+    /// Returns `true` if the solids at `(x1, y1)` and `(x2, y2)` may share a cell —
+    /// i.e. moving one onto the other wouldn't break the "one solid per cell"
+    /// invariant. That holds when at least one cell is empty, or one holds the
+    /// player and the other a **grab** thing (the player collects it).
     ///
-    /// Convenience inverse of [`solid_at`](Board::solid_at).
-    /// Panics if `x` or `y` are out of bounds.
+    /// Off-board coordinates are never combinable (returns `false` rather than
+    /// panicking). Backs the script-facing `combinable(x1, y1, x2, y2)` fn.
     pub fn is_combinable(&self, x1: usize, y1: usize, x2: usize, y2: usize) -> bool {
         // Are either out of bounds?
         if !self.in_bounds((x1 as i32, y1 as i32)) || !self.in_bounds((x2 as i32, y2 as i32)) {