Tree Runtime
src/tree/ composes the pool (subtree.zig), handles (node.zig), traversal (cursor.zig), position shifting (edit.zig), and diffing (changed_ranges.zig) behind the owning Tree facade. Error aggregation is bottom-up at construction time (has_error set from children), so tree.hasError() is O(1). applyEdit maps every stored position through the edit translation; changedRanges re-derives minimal diffs structurally without needing the original edit.