A distributed trace as nested rows with offset and duration bars on a time ruler. Collapse and expand, critical-path highlight, error spans (icon and text, not only colour), a detail slot for the selected span, and a windowed list above 500 rows. Tree semantics (role tree and treeitem, aria-level, aria-expanded, aria-selected) with aria-activedescendant, so the keyboard works the same when rows are windowed.