Get a workflow run and every sub-workflow run below it

Follows stored parent links (parentStepId → step → run) through every attempt of every step, terminal runs included. runs holds list rows without context, root first. hasOpenWork is true while any run in the tree is live, has a pending, running or waiting step, a queued retry, an open task or a pending approval; after a cancel it turns false once the tree has settled. Both come from one read snapshot. The tree is not paginated. Links that form a cycle or nest deeper than 32 levels return 409.