After deleting keys, the tree trim loop could reduce root_layer below what remaining keys require. findKey and deleteFromNode then computed layer - 1 with layer=0, causing u32 underflow. Fixed by changing the height == layer check to height >= layer (handles keys above the current layer) and adding a layer == 0 early-return guard before recursion. The insert-50-delete-every-other stress test now passes, validating that the tree structure remains consistent after bulk deletions. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>