fix(tree): refresh loaded branches on reconnect so they don't go stale (#159)

Third tree-sync finding (#8). On a socket reconnect after a missed-events gap
(laptop sleep / wifi blip), the resync only invalidated the ROOT sidebar query;
a move/rename/delete that happened INSIDE an already-loaded, expanded branch was
never reflected — the branch stayed stale until the user manually interacted.
(The #2 fix reconciles the root level; this covers the deeper loaded branches.)

- `treeModel.reconcileChildren(tree, parentId, fresh)`: replace a loaded
  branch's DIRECT children with the authoritative fresh set (drop removed, add
  new, reorder to server) while PRESERVING each surviving child's already-loaded
  grandchildren, so deeper expansion is not collapsed. An unloaded branch
  (children === undefined) is left untouched (lazy-load fetches it fresh).
- `loadedOpenBranchIds(tree, openIds)`: the branches a reconnect should refresh
  (open AND loaded). `fetchAllAncestorChildren(..., { fresh: true })` bypasses
  the 30-min sidebar cache so the reconcile sees current data (handler-order
  independent).
- space-tree: on socket `connect`, re-fetch + reconcile each open loaded branch
  of the active space (space-switch-guarded; an unloaded branch is skipped).

Tests: reconcileChildren (drop/add/reorder + preserve grandchildren + unloaded
no-op) and loadedOpenBranchIds (open+loaded only, skip unloaded, nested). The
pure logic is unit-tested; the live socket-reconnect round-trip is not
browser-automated (simulating a reconnect gap is impractical) — sidebar render +
expand were smoke-tested with no regression.

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

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

@@ -274,7 +274,10 @@ export function useRestorePageMutation() {
       queryClient.setQueryData<IPage>(["pages", restoredPage.slugId], merge);
     },
     onError: (error) => {
-      notifications.show({ message: t("Failed to restore page"), color: "red" });
+      notifications.show({
+        message: t("Failed to restore page"),
+        color: "red",
+      });
     },
   });
 }
@@ -285,10 +288,10 @@ export function useGetSidebarPagesQuery(
   return useInfiniteQuery({
     queryKey: ["sidebar-pages", data],
     enabled: !!data?.pageId || !!data?.spaceId,
-    queryFn: ({ pageParam }) => getSidebarPages({ ...data, cursor: pageParam, limit: 100 }),
+    queryFn: ({ pageParam }) =>
+      getSidebarPages({ ...data, cursor: pageParam, limit: 100 }),
     initialPageParam: undefined,
-    getNextPageParam: (lastPage) =>
-      lastPage.meta?.nextCursor ?? undefined,
+    getNextPageParam: (lastPage) => lastPage.meta?.nextCursor ?? undefined,
   });
 }
 
@@ -296,11 +299,14 @@ export function useGetRootSidebarPagesQuery(data: SidebarPagesParams) {
   return useInfiniteQuery({
     queryKey: ["root-sidebar-pages", data.spaceId],
     queryFn: async ({ pageParam }) => {
-      return getSidebarPages({ spaceId: data.spaceId, cursor: pageParam, limit: 100 });
+      return getSidebarPages({
+        spaceId: data.spaceId,
+        cursor: pageParam,
+        limit: 100,
+      });
     },
     initialPageParam: undefined,
-    getNextPageParam: (lastPage) =>
-      lastPage.meta?.nextCursor ?? undefined,
+    getNextPageParam: (lastPage) => lastPage.meta?.nextCursor ?? undefined,
   });
 }
 
@@ -323,12 +329,17 @@ export function usePageBreadcrumbsQuery(
   });
 }
 
-export async function fetchAllAncestorChildren(params: SidebarPagesParams) {
+export async function fetchAllAncestorChildren(
+  params: SidebarPagesParams,
+  // `fresh: true` forces a server refetch (staleTime 0) — used by the reconnect
+  // refresh (#159 #8), which must NOT receive the 30-min-cached children.
+  opts?: { fresh?: boolean },
+) {
   // not using a hook here, so we can call it inside a useEffect hook
   const response = await queryClient.fetchQuery({
     queryKey: ["sidebar-pages", params],
     queryFn: () => getAllSidebarPages(params),
-    staleTime: 30 * 60 * 1000,
+    staleTime: opts?.fresh ? 0 : 30 * 60 * 1000,
   });
 
   const allItems = response.pages.flatMap((page) => page.items);
@@ -347,11 +358,15 @@ export function useRecentChangesQuery(spaceId?: string) {
   });
 }
 
-export function useCreatedByQuery(params?: { userId?: string; spaceId?: string }) {
+export function useCreatedByQuery(params?: {
+  userId?: string;
+  spaceId?: string;
+}) {
   const { userId, spaceId } = params ?? {};
   return useInfiniteQuery({
     queryKey: ["pages-created-by-user", { userId, spaceId }],
-    queryFn: ({ pageParam }) => getCreatedByPages({ userId, spaceId, cursor: pageParam, limit: 15 }),
+    queryFn: ({ pageParam }) =>
+      getCreatedByPages({ userId, spaceId, cursor: pageParam, limit: 15 }),
     initialPageParam: undefined as string | undefined,
     getNextPageParam: (lastPage) =>
       lastPage.meta.hasNextPage ? lastPage.meta.nextCursor : undefined,

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

@@ -29,9 +29,11 @@ import {
   collectBranchIds,
   openBranches,
   closeIds,
+  loadedOpenBranchIds,
 } from "@/features/page/tree/utils/utils.ts";
 import { SpaceTreeNode } from "@/features/page/tree/types.ts";
 import { treeModel } from "@/features/page/tree/model/tree-model";
+import { socketAtom } from "@/features/websocket/atoms/socket-atom.ts";
 import {
   getPageBreadcrumbs,
   getSpaceTree,
@@ -39,11 +41,7 @@ import {
 import { IPage } from "@/features/page/types/page.types.ts";
 import { extractPageSlugId } from "@/lib";
 import { isCompactPageTreeEnabled } from "@/lib/config.ts";
-import {
-  DocTree,
-  ROW_HEIGHT_COMPACT,
-  ROW_HEIGHT_STANDARD,
-} from "./doc-tree";
+import { DocTree, ROW_HEIGHT_COMPACT, ROW_HEIGHT_STANDARD } from "./doc-tree";
 import { SpaceTreeRow } from "./space-tree-row";
 
 interface SpaceTreeProps {
@@ -193,6 +191,54 @@ const SpaceTree = forwardRef<SpaceTreeApi, SpaceTreeProps>(function SpaceTree(
     [openTreeNodes],
   );
 
+  // Latest tree + open-state for the reconnect handler (its closure would
+  // otherwise read stale snapshots).
+  const [socket] = useAtom(socketAtom);
+  const dataRef = useRef(data);
+  dataRef.current = data;
+  const openIdsRef = useRef(openIds);
+  openIdsRef.current = openIds;
+
+  // Reconnect refresh (#159 #8): on a socket reconnect, re-fetch and reconcile
+  // the children of every currently-open, already-loaded branch of THIS space,
+  // so a move/rename/delete that happened INSIDE a loaded branch while events
+  // were missed (laptop sleep / wifi gap) is reflected instead of left stale.
+  // The ROOT level is reconciled separately by the root-query refetch +
+  // mergeRootTrees; an UNLOADED branch is skipped (lazy-load fetches it fresh on
+  // expand). No first-connect guard is needed: space-tree usually mounts AFTER
+  // the initial connect, so every `connect` it sees is a reconnect; the rare
+  // initial-connect case has an empty tree, so the refresh is a harmless no-op.
+  useEffect(() => {
+    if (!socket) return;
+    const onConnect = async () => {
+      const effectSpaceId = spaceIdRef.current;
+      const branchIds = loadedOpenBranchIds(
+        dataRef.current.filter((n) => n?.spaceId === effectSpaceId),
+        openIdsRef.current,
+      );
+      if (branchIds.length === 0) return;
+      for (const id of branchIds) {
+        try {
+          // `fresh: true` bypasses the 30-min sidebar-pages cache so the
+          // reconcile sees the server's CURRENT children (handler-order
+          // independent — no reliance on the global reconnect invalidation).
+          const fresh = await fetchAllAncestorChildren(
+            { pageId: id, spaceId: effectSpaceId },
+            { fresh: true },
+          );
+          if (spaceIdRef.current !== effectSpaceId) return; // space switched
+          setData((prev) => treeModel.reconcileChildren(prev, id, fresh));
+        } catch (err) {
+          console.error("[tree] reconnect branch refresh failed", err);
+        }
+      }
+    };
+    socket.on("connect", onConnect);
+    return () => {
+      socket.off("connect", onConnect);
+    };
+  }, [socket, setData]);
+
   const handleToggle = useCallback(
     async (id: string, isOpen: boolean) => {
       setOpenTreeNodes((prev) => ({ ...prev, [id]: isOpen }));
@@ -245,8 +291,7 @@ const SpaceTree = forwardRef<SpaceTreeApi, SpaceTreeProps>(function SpaceTree(
       notifications.show({
         color: "red",
         message: t("Couldn't expand the tree: {{reason}}", {
-          reason:
-            err?.response?.data?.message ?? err?.message ?? String(err),
+          reason: err?.response?.data?.message ?? err?.message ?? String(err),
         }),
       });
     } finally {
@@ -262,11 +307,11 @@ const SpaceTree = forwardRef<SpaceTreeApi, SpaceTreeProps>(function SpaceTree(
     setOpenTreeNodes((prev) => closeIds(prev, ids));
   }, [filteredData, setOpenTreeNodes]);
 
-  useImperativeHandle(
-    ref,
-    () => ({ expandAll, collapseAll, isExpanding }),
-    [expandAll, collapseAll, isExpanding],
-  );
+  useImperativeHandle(ref, () => ({ expandAll, collapseAll, isExpanding }), [
+    expandAll,
+    collapseAll,
+    isExpanding,
+  ]);
 
   // Stable callbacks for DocTree. Without these, every parent render recreates
   // the props and tears down every row's draggable/dropTarget subscription,

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

@@ -255,6 +255,51 @@ describe("treeModel.insertByPosition", () => {
   });
 });
 
+// reconcileChildren (#159 #8): on a socket-reconnect refresh, an already-loaded
+// branch is reconciled against a fresh server fetch — removed children drop,
+// new ones appear, order follows the server, and surviving children keep their
+// own loaded grandchildren (deeper expansion is not collapsed).
+describe("treeModel.reconcileChildren", () => {
+  type N = TreeNode<{ name: string }>;
+  const leaf = (id: string): N => ({ id, name: id.toUpperCase() });
+
+  it("drops removed children, adds new ones, and follows the fresh order", () => {
+    const tree: N[] = [
+      { id: "p", name: "P", children: [leaf("a"), leaf("b")] },
+    ];
+    // Server now has b, c (a was deleted/moved away; c is new) in this order.
+    const next = treeModel.reconcileChildren(tree, "p", [leaf("b"), leaf("c")]);
+    expect(treeModel.find(next, "p")?.children?.map((n) => n.id)).toEqual([
+      "b",
+      "c",
+    ]);
+    expect(treeModel.find(next, "a")).toBeNull();
+  });
+
+  it("preserves a surviving child's loaded grandchildren", () => {
+    const tree: N[] = [
+      {
+        id: "p",
+        name: "P",
+        children: [{ id: "a", name: "A", children: [leaf("a1")] }, leaf("b")],
+      },
+    ];
+    // Fresh fetch returns only top-level children (no grandchildren).
+    const next = treeModel.reconcileChildren(tree, "p", [leaf("a"), leaf("b")]);
+    // 'a' keeps its previously loaded grandchild 'a1'.
+    expect(treeModel.find(next, "a")?.children?.map((n) => n.id)).toEqual([
+      "a1",
+    ]);
+  });
+
+  it("leaves an UNLOADED parent (children undefined) untouched", () => {
+    const tree: N[] = [{ id: "p", name: "P" }]; // children: undefined
+    const next = treeModel.reconcileChildren(tree, "p", [leaf("a")]);
+    expect(next).toBe(tree); // no-op: lazy-load handles an unloaded branch
+    expect(treeModel.find(next, "p")?.children).toBeUndefined();
+  });
+});
+
 // addTreeNode idempotency: the receiver early-returns when the node id already
 // exists, so re-delivery (or the author's optimistic node) is never duplicated.
 // This guards the find-then-skip contract insertByPosition relies on.

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

@@ -223,6 +223,48 @@ export const treeModel = {
     return touched ? out : tree;
   },
 
+  // Replace a parent's DIRECT children with the authoritative `fresh` set while
+  // PRESERVING each surviving child's already-loaded grandchildren (deeper
+  // expansion). Unlike `appendChildren` (add-only), this DROPS children that are
+  // no longer present and reorders to `fresh` — so a move/delete/rename that
+  // happened inside a loaded branch while events were missed (a socket reconnect
+  // gap) is reflected, not left stale (#159 #8). Only used to reconcile an
+  // already-loaded branch against a fresh fetch; a parent with no loaded children
+  // (`children === undefined`) is left untouched (lazy-load handles it).
+  reconcileChildren<T extends object>(
+    tree: TreeNode<T>[],
+    parentId: string,
+    fresh: TreeNode<T>[],
+  ): TreeNode<T>[] {
+    let touched = false;
+    const walk = (nodes: TreeNode<T>[]): TreeNode<T>[] =>
+      nodes.map((n) => {
+        if (n.id === parentId) {
+          // Only reconcile a branch whose children were actually loaded; an
+          // unloaded parent stays unloaded (lazy-load fetches it fresh later).
+          if (n.children === undefined) return n;
+          const prevById = new Map(n.children.map((c) => [c.id, c]));
+          const merged = fresh.map((f) => {
+            const prev = prevById.get(f.id);
+            // Preserve the surviving child's previously loaded grandchildren so
+            // deeper expansion is not collapsed by the reconcile.
+            return prev?.children !== undefined
+              ? { ...f, children: prev.children }
+              : f;
+          });
+          touched = true;
+          return { ...n, children: merged };
+        }
+        if (n.children) {
+          const next = walk(n.children);
+          if (next !== n.children) return { ...n, children: next };
+        }
+        return n;
+      });
+    const out = walk(tree);
+    return touched ? out : tree;
+  },
+
   place<T extends object>(
     tree: TreeNode<T>[],
     sourceId: string,

apps/client/src/features/page/tree/utils/utils.test.ts

@@ -7,6 +7,7 @@ import {
   openBranches,
   closeIds,
   mergeRootTrees,
+  loadedOpenBranchIds,
 } from "./utils";
 import type { IPage } from "@/features/page/types/page.types.ts";
 import type { SpaceTreeNode } from "@/features/page/tree/types.ts";
@@ -321,3 +322,41 @@ describe("mergeRootTrees (#159 #2 reconnect reconcile)", () => {
     expect(merged[0].name).toBe("NEW");
   });
 });
+
+describe("loadedOpenBranchIds (#159 #8 reconnect refresh targets)", () => {
+  function n(id: string, children?: SpaceTreeNode[]): SpaceTreeNode {
+    return {
+      id,
+      slugId: `slug-${id}`,
+      name: id.toUpperCase(),
+      icon: undefined,
+      position: "a0",
+      spaceId: "space-1",
+      parentPageId: null as unknown as string,
+      hasChildren: !!children,
+      children: children as SpaceTreeNode[],
+    };
+  }
+
+  it("returns OPEN branches whose children are loaded (array)", () => {
+    const tree = [n("a", [n("a1")]), n("b", [n("b1")])];
+    const ids = loadedOpenBranchIds(tree, new Set(["a"]));
+    expect(ids).toEqual(["a"]); // b is closed; a is open+loaded
+  });
+
+  it("skips an open branch whose children are NOT loaded (undefined)", () => {
+    const tree = [n("a")]; // children undefined
+    expect(loadedOpenBranchIds(tree, new Set(["a"]))).toEqual([]);
+  });
+
+  it("includes a loaded-but-empty open branch (a child may have been added during the gap)", () => {
+    const tree = [n("a", [])];
+    expect(loadedOpenBranchIds(tree, new Set(["a"]))).toEqual(["a"]);
+  });
+
+  it("walks nested open+loaded branches (deep chain refreshes every level)", () => {
+    const tree = [n("a", [n("a1", [n("a1a")])])];
+    const ids = loadedOpenBranchIds(tree, new Set(["a", "a1"]));
+    expect(ids.sort()).toEqual(["a", "a1"]);
+  });
+});

apps/client/src/features/page/tree/utils/utils.ts

@@ -246,6 +246,29 @@ export function mergeRootTrees(
   return sortPositionKeys(reconciled);
 }
 
+/**
+ * Ids of branches a socket-reconnect refresh should re-fetch and reconcile
+ * (#159 #8): a node that is currently OPEN and whose children are LOADED
+ * (`children` is an array — possibly empty). An unloaded branch (`children ===
+ * undefined`) is skipped because lazy-load fetches it fresh on the next expand,
+ * so there is nothing stale to reconcile. Walks the whole tree (a deep open
+ * chain refreshes every loaded level).
+ */
+export function loadedOpenBranchIds(
+  tree: SpaceTreeNode[],
+  openIds: ReadonlySet<string>,
+): string[] {
+  const ids: string[] = [];
+  const walk = (nodes: SpaceTreeNode[]) => {
+    for (const n of nodes) {
+      if (openIds.has(n.id) && Array.isArray(n.children)) ids.push(n.id);
+      if (n.children) walk(n.children);
+    }
+  };
+  walk(tree);
+  return ids;
+}
+
 // Collect every node id in the tree (roots, branches, leaves). Used by
 // collapseAll to clear the open-state map for all current-space nodes.
 export function collectAllIds(nodes: SpaceTreeNode[]): string[] {