fix(#344 review F1-F4): test-mock coverage + getSpaces freshness + comment/test fixes

- F1 [blocking]: share-modal.test.tsx + comment-content-view.test.tsx mocked
  page-query without usePageMetaQuery → 3 tests threw (ShareModal uses it
  directly, comment-content-view via MentionContent). Added usePageMetaQuery to
  both mocks (the space-tree mocks were already fixed; these two were missed).
- F2: restored refetchOnMount:true on useGetSpacesQuery — ["spaces"] is
  invalidated only by same-tab mutations (no socket path), so a cross-actor
  change (an admin adding/removing THIS user from a space) left the list stale
  until a hard reload. The other refetchOnMount removals (favorites/watched —
  per-user, same-tab-only gap) stay removed.
- F3: corrected the trash-list + recent-changes KEEP comments — both keys ARE
  invalidated (trash-list by 3 mutations, recent-changes by page CRUD), but
  invalidateQueries only marks an UNMOUNTED query stale without refetching, so the
  mount refetch closes the gap. The old "never invalidated" wording was wrong and
  risked a maintainer deleting a live invalidation as dead code.
- F4: tests for the two load-bearing pure paths — invalidate-on-update-page (the
  undefined-guard: a title-only event keeps the icon; sibling/unrelated subtrees
  untouched) and breadcrumb-path-equal (equal chain → true; any id/slugId/name/
  icon change or length diff → false; both-null → true). Exported
  breadcrumbPathEqual for the test.

Gate: client tsc 0; the 4 affected/new test files 33 passed.

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

apps/client/src/features/page/components/breadcrumbs/breadcrumb-path-equal.test.ts

@@ -0,0 +1,53 @@
+import { describe, it, expect, vi } from "vitest";
+import { SpaceTreeNode } from "@/features/page/tree/types";
+
+// breadcrumb.tsx transitively imports @/main.tsx (via usePageMetaQuery ->
+// queryClient), whose module body calls ReactDOM.createRoot on a null root in
+// jsdom. Stub it so importing the pure helper under test doesn't run that
+// (breadcrumbPathEqual does not use queryClient, so a dummy is enough).
+vi.mock("@/main.tsx", () => ({ queryClient: {} }));
+
+import { breadcrumbPathEqual } from "./breadcrumb";
+
+// breadcrumbPathEqual is the ONLY point where a false-positive equality would
+// leave a stale/incorrect breadcrumb trail on screen: it decides whether the
+// selectAtom hands back the same reference (no re-render) for the ancestor chain.
+// Pin both directions — a too-loose equality goes stale on a rename; a too-tight
+// one loses the perf win.
+const node = (over: Partial<SpaceTreeNode>): SpaceTreeNode =>
+  ({ id: "a", slugId: "sa", name: "A", icon: "📄", ...over }) as SpaceTreeNode;
+
+describe("breadcrumbPathEqual", () => {
+  it("both null → true", () => {
+    expect(breadcrumbPathEqual(null, null)).toBe(true);
+  });
+
+  it("same reference → true", () => {
+    const p = [node({})];
+    expect(breadcrumbPathEqual(p, p)).toBe(true);
+  });
+
+  it("equal by id/slugId/name/icon (different arrays) → true", () => {
+    expect(breadcrumbPathEqual([node({})], [node({})])).toBe(true);
+  });
+
+  it("one side null → false", () => {
+    expect(breadcrumbPathEqual([node({})], null)).toBe(false);
+    expect(breadcrumbPathEqual(null, [node({})])).toBe(false);
+  });
+
+  it("different length → false", () => {
+    expect(
+      breadcrumbPathEqual([node({})], [node({}), node({ id: "b" })]),
+    ).toBe(false);
+  });
+
+  it.each(["name", "icon", "slugId", "id"] as const)(
+    "a changed %s → false (breadcrumb must re-render)",
+    (field) => {
+      expect(
+        breadcrumbPathEqual([node({})], [node({ [field]: "CHANGED" })]),
+      ).toBe(false);
+    },
+  );
+});

apps/client/src/features/page/components/breadcrumbs/breadcrumb.tsx

@@ -41,7 +41,7 @@ function getTitle(name: string, icon: string) {
  * visually unchanged, so the breadcrumb no longer re-renders on every tree
  * event (it previously subscribed to the whole treeDataAtom).
  */
-function breadcrumbPathEqual(
+export function breadcrumbPathEqual(
   a: SpaceTreeNode[] | null,
   b: SpaceTreeNode[] | null,
 ): boolean {