1. The exported grid track setters (YGNodeStyleSetGridTemplateColumn/Row, their MinMax variants, and the GridAuto equivalents) pass the caller's index straight into Style::setGrid*At, which writes the backing GridTrackList vector through operator[].
2. An index past the current track count (the count set by the matching ...Count resize call) is an out-of-bounds heap write rather than a rejected argument; ASan reports a heap-buffer-overflow write in Style::setGridTemplateColumnAt.
3. Each of the eight indexed setters now checks index < <list>.size() with assertFatalWithNode before forwarding, so an out-of-range index is rejected the same way other public index APIs already are.

Validated with a unit test that fails on the unpatched tree (OOB write under ASan) and passes after, covering the in-range path plus an out-of-range call for all four track lists.