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fix(tree): cycle-guard placeByPosition so out-of-order moves don't drop subtrees (#206)

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ui-state-races-1: the server-authoritative move path (placeByPosition, via
applyMoveTreeNode) lacked the isDescendant cycle guard that drag-drop `move`
has. When move events arrive out of order so the destination parent is still
nested inside the moved node's own subtree, remove(source) dropped the whole
subtree (incl. the future parent) and insertByPosition could not re-place it —
the node and all descendants silently vanished with no error/refetch.

Add the isDescendant guard to placeByPosition (returns same ref, like its other
no-op cases) and short-circuit applyMoveTreeNode on the same condition BEFORE
the placed===prev remove-fallback (which would otherwise still drop the
subtree). Leave the tree untouched so a later corrective event / reconnect
reconcile fixes it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
This commit is contained in:
claude code agent 227
2026-06-26 06:00:26 +03:00
parent c919d4f636
commit 3d47c306fa
4 changed files with 76 additions and 0 deletions
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14
apps/client/src/features/page/tree/model/tree-model.ts
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@@ -294,6 +294,20 @@ export const treeModel = {
const source = treeModel.find(tree, sourceId);
if (!source) return tree;
if (to.parentId !== null && !treeModel.find(tree, to.parentId)) return tree;
// Cycle guard, mirroring `move`'s `isDescendant` check (#206 ui-state-races-1).
// If the destination parent is INSIDE the moved node's own subtree (reachable
// when server-authoritative move events arrive out of order — e.g. X moved
// under Y, then Y under X, but on this receiver Y is still inside X), then
// `remove(sourceId)` would drop the future parent along with the whole subtree
// and `insertByPosition` could not find it again — the node and ALL its
// descendants would silently vanish. Refuse the move and return the same
// reference so callers can detect the no-op and reconcile (refetch) instead.
if (
to.parentId !== null &&
treeModel.isDescendant(tree, sourceId, to.parentId)
) {
return tree;
}
const removed = treeModel.remove(tree, sourceId);
// Reuse the same position-ordered insertion as `insertByPosition` by
// stamping the authoritative position onto the moved node first.