Deleting a parent on a wedged WS used to leave the child cards on
the canvas as orphaned roots until the user manually refreshed.
Why: Canvas.tsx and DetailsTab.tsx both called `removeNode(parentId)`
after `DELETE /workspaces/:id?confirm=true` returned 200. `removeNode`
deliberately re-parents children rather than cascading — it relies on
the per-descendant WORKSPACE_REMOVED WS events the platform emits as
part of the cascade to drop each child individually. When the WS is
unhealthy those events never arrive, so the local store keeps the
children alive (now re-parented to root since their actual parent is
gone).
Fix: new `removeSubtree(rootId)` action on the canvas store mirrors
the server-side cascade — drops the root + every descendant + every
incident edge in one atomic set(). Both delete call sites now use it.
The WS events still arrive when WS is healthy and become idempotent
no-ops because the nodes are already gone.
Why a new action instead of changing removeNode: removeNode's
re-parenting behavior is correct for non-cascading flows (drag-out,
manual node detach in the future). Adding a sibling action keeps
both call shapes available rather than forcing every caller to opt
out of cascade.
6 new unit tests cover root cascade, mid-level cascade, leaf
no-op-cascade, selection clearing across the subtree, selection
preservation outside the subtree, and edge cleanup.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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