diff --git a/apps/app/src/lib/ui-preferences/ui-preferences-sync.test.ts b/apps/app/src/lib/ui-preferences/ui-preferences-sync.test.ts
index c7febce6d..4cb921b89 100644
--- a/apps/app/src/lib/ui-preferences/ui-preferences-sync.test.ts
+++ b/apps/app/src/lib/ui-preferences/ui-preferences-sync.test.ts
@@ -106,6 +106,62 @@ describe("ui preferences sync", () => {
     resetUiPreferencesSyncForTest();
   });
 
+  it("retains a local section order when the initial cache lacks its entry", () => {
+    const { orderAtom, queryClient, store } = createHarness();
+    const localOrder = ["threads", "projects", "pinned"];
+    store.set(orderAtom, localOrder);
+    const response = serverResponse();
+    response.preferences = Object.fromEntries(
+      Object.entries(response.preferences).filter(([key]) => key !== "sidebar.sectionOrder"),
+    ) as UiPreferencesResponse["preferences"];
+    setCachedUiPreferences(queryClient, response);
+
+    startUiPreferencesSync({ queryClient, store });
+
+    expect(store.get(orderAtom)).toEqual(localOrder);
+    expect(mocks.set).not.toHaveBeenCalled();
+  });
+
+  it("keeps edits local without an error notification when the server lacks the entry", async () => {
+    const { orderAtom, queryClient, store } = createHarness();
+    startUiPreferencesSync({ queryClient, store });
+    const response = serverResponse();
+    response.preferences = Object.fromEntries(
+      Object.entries(response.preferences).filter(([key]) => key !== "sidebar.sectionOrder"),
+    ) as UiPreferencesResponse["preferences"];
+    setCachedUiPreferences(queryClient, response);
+
+    store.set(orderAtom, ["threads"]);
+    await waitForUiPreferenceWrites();
+
+    expect(store.get(orderAtom)).toEqual(["threads"]);
+    expect(mocks.set).not.toHaveBeenCalled();
+    expect(mocks.toastError).not.toHaveBeenCalled();
+    expect(hasPendingUiPreferenceWrite("sidebar.sectionOrder")).toBe(false);
+  });
+
+  it("records an acknowledged write after its cached entry disappears", async () => {
+    const { orderAtom, queryClient, store } = createHarness();
+    startUiPreferencesSync({ queryClient, store });
+    setCachedUiPreferences(queryClient, serverResponse());
+    const response = serverResponse();
+    response.preferences = Object.fromEntries(
+      Object.entries(response.preferences).filter(([key]) => key !== "sidebar.sectionOrder"),
+    ) as UiPreferencesResponse["preferences"];
+    mocks.set.mockImplementationOnce(async (input) => {
+      setCachedUiPreferences(queryClient, response);
+      return { key: input.key, revision: 1, value: input.value };
+    });
+
+    store.set(orderAtom, ["threads"]);
+    await waitForUiPreferenceWrites();
+
+    expect(getCachedUiPreferences(queryClient)?.preferences["sidebar.sectionOrder"])
+      .toEqual({ revision: 1, value: ["threads"] });
+    expect(mocks.toastError).not.toHaveBeenCalled();
+    expect(store.get(orderAtom)).toEqual(["threads"]);
+  });
+
   it("keeps writes local when no sync context has started", () => {
     const { modeAtom, store } = createHarness();
     store.set(modeAtom, "machine");