fix(page-tree/dnd): drag авто-раскрытие — задержка 2с, не раскрывать при drop внутрь + guard от потери детей и сигнал «уехало сюда»

Пять точечных клиентских правок (дизайн из адверсариального разбора #523):

1. Задержка hover-раскрытия при drag: `AUTO_EXPAND_MS` 500 → 2000 мс, чтобы
   проведение курсора через дерево не раскрывало ряды — только осознанное
   удержание.
2. Не раскрывать цель при drop внутрь (make-child): удалена строка
   `onToggle(target, true)` в `onDrop` (drop оставляет узел свёрнутым; раскрытие
   только по hover-hold). Восстановление раскрытости самого source не тронуто.
3. Guard от потери детей в `handleMove` (обязателен вместе с п.2): раньше эта же
   `onToggle` была ЕДИНСТВЕННЫМ триггером корректирующего lazy-load. `treeModel.move`
   материализует `target.children = [source]`; для НЕзагруженной цели (предикат
   gate `treeModel.isUnloadedBranch`) это скрыло бы остальных серверных детей папки
   (класс #159 #1). Теперь для незагруженной make-child-цели оптимистичное дерево
   строится БЕЗ материализации source: source удаляется из старого родителя, цели
   ставится `hasChildren:true`; gate остаётся взведён и раскрытие догружает полный
   набор. Для загруженной цели поведение прежнее (append сохраняет детей).
4. Инвалидация крошек: `updateCacheOnMovePage` инвалидирует
   `["breadcrumbs", pageId]` — guard делает `remove(source)`, и для текущей
   открытой страницы `findBreadcrumbPath` промахивается → крошки показывали бы
   старого родителя до refocus.
5. Сигнал «уехало сюда»: транзиентный teal-пульс на строке при make-child-drop в
   свёрнутую цель (узел НЕ раскрывается), отдельный `data-landed-child` +
   `DROP_LANDED_HIGHLIGHT_MS`, таймер чистится при анмаунте; уважает
   prefers-reduced-motion.

Тесты: `handleMove` — незагруженная make-child-цель не материализует `[source]`
(мутация guard'а краснит), загруженная цель append'ит и сохраняет детей,
genuinely-empty лист материализует; инвалидация `["breadcrumbs", pageId]`.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/client/src/features/page/queries/page-query.ts

@@ -665,6 +665,13 @@ export function updateCacheOnMovePage(
   pageData: Partial<IPage>,
 ) {
   invalidatePageTree();
+  // Invalidate the moved page's breadcrumbs (#523). The tree-side child-loss
+  // guard removes the moved node from the local tree when its new parent is an
+  // unloaded branch, so `findBreadcrumbPath` misses it and the breadcrumb bar
+  // falls back to the server `["breadcrumbs", pageId]` query — which this move
+  // must invalidate, otherwise the crumbs keep showing the OLD parent until a
+  // refocus/navigation.
+  queryClient.invalidateQueries({ queryKey: ["breadcrumbs", pageId] });
   // Remove page from old parent's cache
   const oldQueryKey =
     oldParentId === null

apps/client/src/features/page/queries/update-cache-on-move.breadcrumbs.test.ts

@@ -0,0 +1,40 @@
+import { describe, it, expect, beforeEach, vi } from "vitest";
+import type { IPage } from "@/features/page/types/page.types";
+
+// A fresh QueryClient stands in for the app singleton (importing the real
+// @/main.tsx would run ReactDOM.createRoot, which has no DOM root in jsdom).
+vi.mock("@/main.tsx", async () => {
+  const { QueryClient } = await import("@tanstack/react-query");
+  return { queryClient: new QueryClient() };
+});
+
+import { queryClient } from "@/main.tsx";
+import { updateCacheOnMovePage } from "./page-query";
+
+// #523: the tree-side child-loss guard removes the moved node from the local
+// tree when its new parent is an unloaded branch, so `findBreadcrumbPath` misses
+// it and the breadcrumb bar falls back to the server `["breadcrumbs", pageId]`
+// query. That query MUST be invalidated by a move, or the crumbs keep showing
+// the OLD parent until a refocus/navigation.
+describe("updateCacheOnMovePage — breadcrumbs invalidation (#523)", () => {
+  beforeEach(() => {
+    queryClient.clear();
+    vi.restoreAllMocks();
+  });
+
+  it("invalidates the moved page's ['breadcrumbs', pageId] query", () => {
+    const spy = vi.spyOn(queryClient, "invalidateQueries");
+
+    updateCacheOnMovePage("s1", "moved-page", "old-parent", "new-parent", {
+      id: "moved-page",
+    } as Partial<IPage>);
+
+    const invalidatedBreadcrumbs = spy.mock.calls.some(
+      ([arg]) =>
+        Array.isArray((arg as { queryKey?: unknown[] })?.queryKey) &&
+        (arg as { queryKey: unknown[] }).queryKey[0] === "breadcrumbs" &&
+        (arg as { queryKey: unknown[] }).queryKey[1] === "moved-page",
+    );
+    expect(invalidatedBreadcrumbs).toBe(true);
+  });
+});

apps/client/src/features/page/tree/components/doc-tree-row.tsx

@@ -55,7 +55,14 @@ type Props<T extends object> = {
 };
 
 const DRAG_TYPE = 'doc-tree-item';
-const AUTO_EXPAND_MS = 500;
+// Hover-hold before a collapsed row auto-expands during a drag. 2s (not ~0.5s)
+// so merely dragging the cursor THROUGH the tree never expands rows — only a
+// deliberate hold does (#523).
+const AUTO_EXPAND_MS = 2000;
+// How long the "a page just moved in here" cue stays on a collapsed target after
+// a make-child drop. Long enough to notice at a glance during frequent
+// collapsed-drops, short enough not to linger. Code-only UX constant (#523).
+const DROP_LANDED_HIGHLIGHT_MS = 1800;
 
 function DocTreeRowInner<T extends object>(props: Props<T>) {
   const {
@@ -93,7 +100,11 @@ function DocTreeRowInner<T extends object>(props: Props<T>) {
   const rowRef = useRef<HTMLElement>(null);
   const [isDragging, setIsDragging] = useState(false);
   const [instruction, setInstruction] = useState<Instruction | null>(null);
+  // Transient "just received a child" cue: a make-child drop no longer expands
+  // the (collapsed) target, so flash the row instead so the move isn't invisible.
+  const [landedChild, setLandedChild] = useState(false);
   const autoExpandTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null);
+  const landedChildTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null);
 
   const cancelAutoExpand = useCallback(() => {
     if (autoExpandTimerRef.current) {
@@ -249,11 +260,24 @@ function DocTreeRowInner<T extends object>(props: Props<T>) {
               ? getDragLabel(sourceNode)
               : 'item';
             liveRegion.announce(`Moved ${sourceLabel} under ${parentName}.`);
-            // After a make-child drop, expand this row so the user sees the
-            // just-dropped child — especially important when the row had no
-            // children before (chevron just appeared) so the drop would
-            // otherwise be invisible.
-            if (op.kind === 'make-child') onToggle(node.id, true);
+            // Do NOT auto-expand the target on drop: a drop must leave the node
+            // collapsed. Intentional expansion is handled solely by the
+            // hover-hold timer (AUTO_EXPAND_MS). Feedback that the drop landed is
+            // given by the post-move flash + landed-cue highlight + live-region
+            // announce above. When the make-child target is collapsed, flash a
+            // distinct "child moved in here" cue on the row (it stays collapsed).
+            if (op.kind === 'make-child' && !isOpen) {
+              if (landedChildTimerRef.current) {
+                clearTimeout(landedChildTimerRef.current);
+              }
+              setLandedChild(true);
+              landedChildTimerRef.current = setTimeout(() => {
+                setLandedChild(false);
+                landedChildTimerRef.current = null;
+              }, DROP_LANDED_HIGHLIGHT_MS);
+            }
+            // Restore the openness of the MOVED page itself (source) — untouched
+            // by the above; the target is never expanded here.
             if (source.data.isOpenOnDragStart) onToggle(sourceId, true);
           },
         }),
@@ -281,6 +305,17 @@ function DocTreeRowInner<T extends object>(props: Props<T>) {
 
   useEffect(() => () => cancelAutoExpand(), [cancelAutoExpand]);
 
+  // Clear the landed-child cue timer on unmount (mirrors autoExpandTimerRef).
+  useEffect(
+    () => () => {
+      if (landedChildTimerRef.current) {
+        clearTimeout(landedChildTimerRef.current);
+        landedChildTimerRef.current = null;
+      }
+    },
+    [],
+  );
+
   const effectiveInst =
     instruction?.type === 'instruction-blocked'
       ? instruction.desired
@@ -317,6 +352,7 @@ function DocTreeRowInner<T extends object>(props: Props<T>) {
         className={styles.node}
         data-dragging={isDragging || undefined}
         data-selected={isSelected || undefined}
+        data-landed-child={landedChild || undefined}
         data-receiving-drop={
           receivingDrop === 'make-child'
             ? blocked

apps/client/src/features/page/tree/components/space-tree.tsx

@@ -281,10 +281,10 @@ const SpaceTree = forwardRef<SpaceTreeApi, SpaceTreeProps>(function SpaceTree(
       setOpenTreeNodes((prev) => ({ ...prev, [id]: isOpen }));
       if (isOpen) {
         const node = treeModel.find(data, id) as SpaceTreeNode | null;
-        if (
-          node?.hasChildren &&
-          (!node.children || node.children.length === 0)
-        ) {
+        // Same "unloaded branch" predicate the insert paths use (`isUnloadedBranch`)
+        // so the lazy-load gate and the realtime/DnD inserts can never disagree
+        // about what counts as unloaded (#525).
+        if (treeModel.isUnloadedBranch(node)) {
           const fetched = await fetchAllAncestorChildren({
             pageId: id,
             spaceId: node.spaceId,

apps/client/src/features/page/tree/hooks/use-tree-mutation.move-guard.test.tsx

@@ -0,0 +1,149 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { renderHook, act } from "@testing-library/react";
+import { Provider, createStore } from "jotai";
+import type { ReactNode } from "react";
+
+import { treeDataAtom } from "@/features/page/tree/atoms/tree-data-atom.ts";
+import { treeModel } from "@/features/page/tree/model/tree-model";
+import type { SpaceTreeNode } from "@/features/page/tree/types";
+
+// --- Boundary mocks: only the network/query + router/i18n surfaces the hook
+// touches. The tree math (treeModel, dropOpToMovePayload) runs for real so the
+// child-loss guard is exercised end-to-end.
+const moveMutate = vi.fn().mockResolvedValue({});
+const updateCacheOnMovePageMock = vi.fn();
+vi.mock("@/features/page/queries/page-query.ts", () => ({
+  useCreatePageMutation: () => ({ mutateAsync: vi.fn() }),
+  useUpdatePageMutation: () => ({ mutateAsync: vi.fn() }),
+  useRemovePageMutation: () => ({ mutateAsync: vi.fn() }),
+  useMovePageMutation: () => ({ mutateAsync: moveMutate }),
+  updateCacheOnMovePage: (...args: unknown[]) =>
+    updateCacheOnMovePageMock(...args),
+}));
+vi.mock("react-router-dom", () => ({
+  useNavigate: () => vi.fn(),
+  useParams: () => ({ spaceSlug: "space", pageSlug: undefined }),
+}));
+vi.mock("react-i18next", () => ({
+  useTranslation: () => ({ t: (s: string) => s }),
+}));
+vi.mock("@mantine/notifications", () => ({
+  notifications: { show: vi.fn() },
+}));
+
+// Import AFTER mocks so the hook binds to them.
+import { useTreeMutation } from "./use-tree-mutation";
+
+function node(
+  id: string,
+  over: Partial<SpaceTreeNode> = {},
+): SpaceTreeNode {
+  return {
+    id,
+    slugId: `slug-${id}`,
+    name: id.toUpperCase(),
+    position: "a0",
+    spaceId: "space-1",
+    parentPageId: null as unknown as string,
+    hasChildren: false,
+    children: [],
+    ...over,
+  };
+}
+
+function setup(before: SpaceTreeNode[]) {
+  const store = createStore();
+  store.set(treeDataAtom, before);
+  const wrapper = ({ children }: { children: ReactNode }) => (
+    <Provider store={store}>{children}</Provider>
+  );
+  const { result } = renderHook(() => useTreeMutation("space-1"), { wrapper });
+  return { store, result };
+}
+
+describe("useTreeMutation.handleMove — child-loss guard (#523)", () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    moveMutate.mockResolvedValue({});
+  });
+
+  it("make-child into an UNLOADED folder does NOT materialize [source] — keeps it lazy-loadable", async () => {
+    // F has children on the server but none are loaded here (canonical unloaded
+    // form: hasChildren + children:[]). X sits at root.
+    const before = [
+      node("F", { position: "a0", hasChildren: true, children: [] }),
+      node("X", { position: "a5" }),
+    ];
+    const { store, result } = setup(before);
+
+    await act(async () => {
+      await result.current.handleMove("X", {
+        kind: "make-child",
+        targetId: "F",
+      });
+    });
+
+    const tree = store.get(treeDataAtom);
+    const f = treeModel.find(tree, "F");
+    // The guard leaves F unloaded (children stay []), so a later expand fetches
+    // the FULL server set (incl. X) instead of showing a misleading partial [X].
+    // MUTATION: dropping the guard (using the `move` result) would put children
+    // === [X] here and redden this.
+    expect(f?.children).toEqual([]);
+    expect(f?.hasChildren).toBe(true);
+    // X is removed from its old (root) slot; it reappears on expand/load of F.
+    expect(treeModel.find(tree, "X")).toBeNull();
+    // The server move is still persisted.
+    expect(moveMutate).toHaveBeenCalledTimes(1);
+  });
+
+  it("make-child into a LOADED folder appends source and KEEPS the existing children", async () => {
+    // F is loaded with one child c1; moving X in must preserve c1 (no loss) and
+    // append X — this path does NOT hit the guard.
+    const before = [
+      node("F", {
+        position: "a0",
+        hasChildren: true,
+        children: [node("c1", { position: "a1", parentPageId: "F" })],
+      }),
+      node("X", { position: "a5" }),
+    ];
+    const { store, result } = setup(before);
+
+    await act(async () => {
+      await result.current.handleMove("X", {
+        kind: "make-child",
+        targetId: "F",
+      });
+    });
+
+    const tree = store.get(treeDataAtom);
+    const f = treeModel.find(tree, "F");
+    expect(f?.children?.map((n) => n.id)).toEqual(["c1", "X"]);
+    expect(f?.hasChildren).toBe(true);
+    // X now lives under F.
+    expect(treeModel.find(tree, "X")?.parentPageId).toBe("F");
+  });
+
+  it("make-child into a genuinely-empty leaf materializes the child (nothing to lose)", async () => {
+    // Leaf L has no server children (hasChildren:false). Dropping X in should
+    // show X immediately — the guard must NOT fire here.
+    const before = [
+      node("L", { position: "a0", hasChildren: false, children: [] }),
+      node("X", { position: "a5" }),
+    ];
+    const { store, result } = setup(before);
+
+    await act(async () => {
+      await result.current.handleMove("X", {
+        kind: "make-child",
+        targetId: "L",
+      });
+    });
+
+    const tree = store.get(treeDataAtom);
+    const l = treeModel.find(tree, "L");
+    expect(l?.children?.map((n) => n.id)).toEqual(["X"]);
+    expect(l?.hasChildren).toBe(true);
+  });
+});

apps/client/src/features/page/tree/hooks/use-tree-mutation.ts

@@ -61,11 +61,48 @@ export function useTreeMutation(spaceId: string): UseTreeMutation {
       if (!source) return;
       const oldParentId = source.parentPageId ?? null;
 
-      // optimistic apply with the new position from the payload
-      let optimistic = treeModel.update(after, sourceId, {
-        position: payload.position,
-        parentPageId: payload.parentPageId,
-      } as Partial<SpaceTreeNode>);
+      // Child-loss guard (#523, twin of #525's realtime `insertByPosition` fix).
+      // We no longer auto-expand the make-child target on drop, so the old
+      // `onToggle(target, true)` — which was ALSO the only trigger of the
+      // corrective lazy-load — is gone. `treeModel.move` materialized
+      // `target.children = [source]` (only the moved node); if the target is an
+      // UNLOADED branch (server has children but none are loaded here), keeping
+      // that partial `[source]` list would defeat the lazy-load gate and hide the
+      // target's OTHER server children (the #159 #1 data-loss class). So for an
+      // unloaded make-child target, build the optimistic tree WITHOUT
+      // materializing source under it: just remove source from its old parent and
+      // flag the target `hasChildren`. The gate stays armed and a later manual
+      // expand fetches the FULL set (incl. the moved page, which the awaited
+      // server move persists). Predicate is the gate's (`isUnloadedBranch`), NOT
+      // `insertByPosition`'s old `=== undefined` (canonical unloaded is `[]`).
+      const target =
+        op.kind === "make-child"
+          ? (treeModel.find(before, op.targetId) as SpaceTreeNode | null)
+          : null;
+      const unloadedMakeChild =
+        op.kind === "make-child" && treeModel.isUnloadedBranch(target);
+
+      let optimistic: SpaceTreeNode[];
+      if (unloadedMakeChild) {
+        // Do NOT materialize [source] into the unloaded target.
+        optimistic = treeModel.remove(before, sourceId);
+        optimistic = treeModel.update(optimistic, op.targetId, {
+          hasChildren: true,
+        } as Partial<SpaceTreeNode>);
+      } else {
+        // optimistic apply with the new position from the payload
+        optimistic = treeModel.update(after, sourceId, {
+          position: payload.position,
+          parentPageId: payload.parentPageId,
+        } as Partial<SpaceTreeNode>);
+        // For make-child onto a previously-childless (loaded) target: flip
+        // hasChildren on so the new parent shows its chevron.
+        if (op.kind === "make-child") {
+          optimistic = treeModel.update(optimistic, op.targetId, {
+            hasChildren: true,
+          } as Partial<SpaceTreeNode>);
+        }
+      }
 
       // If the old parent has no children left, mark hasChildren: false so the
       // chevron disappears. Without this, the empty parent keeps rendering an
@@ -79,14 +116,6 @@ export function useTreeMutation(spaceId: string): UseTreeMutation {
         }
       }
 
-      // For make-child onto a previously-childless target: flip hasChildren on
-      // so the new parent shows its chevron.
-      if (op.kind === "make-child") {
-        optimistic = treeModel.update(optimistic, op.targetId, {
-          hasChildren: true,
-        } as Partial<SpaceTreeNode>);
-      }
-
       setData(optimistic);
 
       try {

apps/client/src/features/page/tree/model/tree-model.test.ts

@@ -74,6 +74,48 @@ describe("treeModel.isDescendant", () => {
   });
 });
 
+// #525: the single "is this branch unloaded?" predicate shared by the lazy-load
+// gate and the insert paths. Unloaded == server says hasChildren but none are
+// present locally (canonical form `children: []`, also `undefined`). A parent
+// without hasChildren is genuinely empty, not unloaded.
+describe("treeModel.isUnloadedBranch", () => {
+  type PH = TreeNode<{ name: string; hasChildren?: boolean }>;
+  it("true for hasChildren + empty array (canonical unloaded form)", () => {
+    const n: PH = { id: "p", name: "P", hasChildren: true, children: [] };
+    expect(treeModel.isUnloadedBranch(n)).toBe(true);
+  });
+  it("true for hasChildren + undefined children", () => {
+    const n: PH = { id: "p", name: "P", hasChildren: true };
+    expect(treeModel.isUnloadedBranch(n)).toBe(true);
+  });
+  it("false for hasChildren + already-loaded children", () => {
+    const n: PH = {
+      id: "p",
+      name: "P",
+      hasChildren: true,
+      children: [{ id: "c", name: "C" }],
+    };
+    expect(treeModel.isUnloadedBranch(n)).toBe(false);
+  });
+  it("false for a genuinely-empty parent (no hasChildren)", () => {
+    expect(
+      treeModel.isUnloadedBranch({
+        id: "p",
+        name: "P",
+        hasChildren: false,
+        children: [],
+      } as PH),
+    ).toBe(false);
+    expect(
+      treeModel.isUnloadedBranch({ id: "p", name: "P" } as PH),
+    ).toBe(false);
+  });
+  it("false for null/undefined", () => {
+    expect(treeModel.isUnloadedBranch(null)).toBe(false);
+    expect(treeModel.isUnloadedBranch(undefined)).toBe(false);
+  });
+});
+
 describe("treeModel.visible", () => {
   it("returns only root nodes when no openIds", () => {
     const v = treeModel.visible(fixture, new Set());
@@ -197,43 +239,64 @@ describe("treeModel.insertByPosition", () => {
     ]);
   });
 
-  // #159 #1: inserting/moving a node under a parent whose children are NOT
-  // loaded (`children === undefined`, e.g. a collapsed page) must NOT materialize
-  // a partial `[node]` list — that would defeat the lazy-load gate and hide the
-  // parent's other real children. The node is left to be lazy-loaded; only
-  // `hasChildren` is flagged so the chevron appears.
-  it("does NOT materialize a child under an UNLOADED parent (children undefined)", () => {
-    type PH = TreeNode<{
-      name: string;
-      position?: string;
-      hasChildren?: boolean;
-    }>;
+  type PH = TreeNode<{
+    name: string;
+    position?: string;
+    hasChildren?: boolean;
+  }>;
+
+  // #159 #1 / #525: inserting/moving a node under an UNLOADED parent must NOT
+  // materialize a partial `[node]` list — that would defeat the lazy-load gate and
+  // hide the parent's other real children. The canonical unloaded form here is
+  // `children: []` + `hasChildren: true` (from `pageToTreeNode` /
+  // `pruneCollapsedChildren`), which the pre-#525 `=== undefined` guard MISSED.
+  // The node is left to be lazy-loaded; the chevron stays enabled.
+  it("does NOT materialize a child under an UNLOADED parent (children: [], hasChildren: true)", () => {
     const tree: PH[] = [
-      { id: "p", name: "P", position: "a0", hasChildren: false }, // children: undefined
+      { id: "p", name: "P", position: "a0", hasChildren: true, children: [] },
     ];
     const node: PH = { id: "x", name: "X", position: "a1" };
     const t = treeModel.insertByPosition(tree, "p", node);
     const parent = treeModel.find(t, "p");
     // The node was NOT inserted (children stay unloaded -> lazy-load fetches the
-    // full set, including this node, on expand).
-    expect(parent?.children).toBeUndefined();
+    // full set, including this node, on expand). MUTATION: the pre-#525 predicate
+    // `children === undefined` does not fire for `[]`, so it would insert `[x]`
+    // here and reredden this expectation.
+    expect(parent?.children).toEqual([]);
     expect(treeModel.find(t, "x")).toBeNull();
-    // ...but the chevron is enabled so the user can expand to load it.
+    // ...and the chevron stays enabled so the user can expand to load it.
     expect((parent as PH).hasChildren).toBe(true);
   });
 
-  it("DOES insert under a LOADED-but-empty parent (children: [])", () => {
-    type PH = TreeNode<{
-      name: string;
-      position?: string;
-      hasChildren?: boolean;
-    }>;
+  it("does NOT materialize a child under an UNLOADED parent (children undefined, hasChildren: true)", () => {
+    const tree: PH[] = [
+      { id: "p", name: "P", position: "a0", hasChildren: true }, // children: undefined
+    ];
+    const node: PH = { id: "x", name: "X", position: "a1" };
+    const t = treeModel.insertByPosition(tree, "p", node);
+    const parent = treeModel.find(t, "p");
+    expect(parent?.children).toBeUndefined();
+    expect(treeModel.find(t, "x")).toBeNull();
+    expect((parent as PH).hasChildren).toBe(true);
+  });
+
+  it("DOES insert under a genuinely-empty parent (children: [], hasChildren: false)", () => {
     const tree: PH[] = [
       { id: "p", name: "P", position: "a0", hasChildren: false, children: [] },
     ];
     const node: PH = { id: "x", name: "X", position: "a1" };
     const t = treeModel.insertByPosition(tree, "p", node);
-    // A loaded (empty) child list is complete, so the node IS inserted.
+    // No server children (`hasChildren: false`), so materializing the first child
+    // is correct — nothing is hidden.
+    expect(treeModel.find(t, "p")?.children?.map((n) => n.id)).toEqual(["x"]);
+  });
+
+  it("DOES insert under a genuinely-empty parent (children undefined, hasChildren: false)", () => {
+    const tree: PH[] = [
+      { id: "p", name: "P", position: "a0", hasChildren: false }, // children: undefined
+    ];
+    const node: PH = { id: "x", name: "X", position: "a1" };
+    const t = treeModel.insertByPosition(tree, "p", node);
     expect(treeModel.find(t, "p")?.children?.map((n) => n.id)).toEqual(["x"]);
   });
 

apps/client/src/features/page/tree/model/tree-model.ts

@@ -43,6 +43,24 @@ export const treeModel = {
     };
   },
 
+  // A branch is "unloaded" when the server says it HAS children (`hasChildren`)
+  // but none are present locally. The canonical unloaded form in this codebase
+  // is `children: []` (produced by `pageToTreeNode` and by `pruneCollapsedChildren`
+  // resetting collapsed branches), NOT `children: undefined` — so a predicate that
+  // only checks `=== undefined` misses the real case and materializes a misleading
+  // partial list (#525). This is the SINGLE source of truth for "should a
+  // fetch/materialize be deferred?", shared by the lazy-load gate (`handleToggle`),
+  // the realtime insert path (`insertByPosition`) and the DnD move guard, so they
+  // can never drift apart again. A parent WITHOUT `hasChildren` is genuinely empty
+  // (no server children) — inserting its first child is correct, not deferred.
+  isUnloadedBranch<T extends object>(
+    node: TreeNode<T> | null | undefined,
+  ): boolean {
+    if (!node) return false;
+    const hasChildren = (node as { hasChildren?: boolean }).hasChildren === true;
+    return hasChildren && (node.children == null || node.children.length === 0);
+  },
+
   isDescendant<T extends object>(
     tree: TreeNode<T>[],
     ancestorId: string,
@@ -127,14 +145,15 @@ export const treeModel = {
     }
     const parent = treeModel.find(tree, parentId);
     // The parent is in the tree but its children have NOT been lazy-loaded yet
-    // (`children === undefined`, distinct from a loaded-but-empty `[]`). Inserting
+    // (`hasChildren` set + children absent/empty — see `isUnloadedBranch`; the
+    // canonical unloaded form is `children: []`, NOT just `undefined`). Inserting
     // here would MATERIALIZE a misleading partial child list (`[node]`) that
     // defeats the lazy-load gate — which fetches only when children are
     // absent/empty — so the parent's OTHER real children would never load and the
     // moved/added node would be the only one shown (a silent data loss, #159 #1).
     // Instead, leave the children unloaded and just flag `hasChildren` so the
     // chevron appears; expanding fetches the FULL set (including this node).
-    if (parent && parent.children === undefined) {
+    if (parent && treeModel.isUnloadedBranch(parent)) {
       return treeModel.update(
         tree,
         parentId,

apps/client/src/features/page/tree/styles/tree.module.css

@@ -150,6 +150,45 @@
     );
 }
 
+/* "A page just moved in here" cue (#523). A make-child drop no longer expands
+   the collapsed target, so the moved page is momentarily invisible; pulse the
+   target row in a distinct teal (NOT the blue make-child highlight, NOT the
+   neutral post-move flash) so the landing is noticeable while the node stays
+   collapsed. Two short pulses fit inside DROP_LANDED_HIGHLIGHT_MS (1.8s), after
+   which the row clears the attribute and the animation stops. */
+@keyframes landedChildPulse {
+    0% {
+        background-color: light-dark(
+            var(--mantine-color-teal-2),
+            rgba(45, 212, 191, 0.30)
+        );
+        outline-color: light-dark(
+            var(--mantine-color-teal-6),
+            var(--mantine-color-teal-5)
+        );
+    }
+    100% {
+        background-color: transparent;
+        outline-color: transparent;
+    }
+}
+
+.node[data-landed-child="true"] {
+    outline: 2px solid transparent;
+    outline-offset: -1px;
+    animation: landedChildPulse 0.9s ease-out 2;
+}
+
+@media (prefers-reduced-motion: reduce) {
+    .node[data-landed-child="true"] {
+        animation: none;
+        background-color: light-dark(
+            var(--mantine-color-teal-1),
+            rgba(45, 212, 191, 0.18)
+        );
+    }
+}
+
 .dropLine {
     position: absolute;
     left: var(--drop-line-indent, 0);

apps/client/src/features/websocket/tree-socket-reducers.test.ts

@@ -82,17 +82,19 @@ describe("applyMoveTreeNode", () => {
     ]);
   });
 
-  it("does NOT create a partial child list when the destination is loaded-but-collapsed (children unloaded) — keeps it lazy-loadable (#159)", () => {
-    // `dstCollapsed` is in the tree but its children were never lazy-loaded
-    // (children === undefined). The OLD behavior inserted `src` as the ONLY
-    // child ([src]), which defeated the lazy-load gate and HID the parent's
-    // other real children. Now the move leaves children unloaded (so expanding
-    // fetches the FULL set, including src) and just flags hasChildren.
+  it("does NOT create a partial child list when the destination is loaded-but-collapsed (children unloaded) — keeps it lazy-loadable (#159 #525)", () => {
+    // `dstCollapsed` is in the tree but its children were never lazy-loaded. The
+    // CANONICAL unloaded form here is `hasChildren: true` + `children: []` (from
+    // `pageToTreeNode` / `pruneCollapsedChildren`), NOT `children: undefined`.
+    // The pre-#525 predicate (`children === undefined`) missed this form and
+    // inserted `src` as the ONLY child ([src]), defeating the lazy-load gate and
+    // HIDING the parent's other real children. Now the move leaves children
+    // unloaded (so expanding fetches the FULL set, including src).
     const tree: SpaceTreeNode[] = [
       node("dstCollapsed", {
         position: "a0",
-        hasChildren: false,
-        children: undefined as unknown as SpaceTreeNode[],
+        hasChildren: true,
+        children: [],
       }),
       node("src", { position: "a9" }),
     ];
@@ -105,9 +107,10 @@ describe("applyMoveTreeNode", () => {
       pageData: {},
     });
     const dst = treeModel.find(next, "dstCollapsed");
-    // Children stay unloaded -> the lazy-load gate fetches the FULL set (incl.
-    // src) on expand, rather than showing a misleading partial [src] list.
-    expect(dst?.children).toBeUndefined();
+    // Children stay unloaded ([] not materialized to [src]) -> the lazy-load gate
+    // fetches the FULL set (incl. src) on expand. MUTATION: the pre-#525
+    // `=== undefined` predicate would insert [src] here and redden this.
+    expect(dst?.children).toEqual([]);
     expect(dst?.hasChildren).toBe(true);
     // src moved away from its old root slot (it lives under dstCollapsed
     // server-side and reappears when the parent is expanded/loaded).