test(ui): 侧栏只读模式、共享外壳与列表缓存的合同回归

新增 8 条：`sidebar-data-cache.test.ts`（命中不重拉 / 过期重拉一次 / 写操作后
拿到新标题并逐条锁住五个写路径 / 双账户不串 / 只存内存 / 401 清空）、
`sidebar-state.test.ts` +2（收起后重挂仍收起，含三种降级；移动端不读不写）、
`sidebar-contract.test.ts` +1（只读模式只少三样）、`chart-page-view.test.tsx` +1
（`(secondary)` layout 恰好挂一份只读侧栏，数据 hook 无写方法）。

改写 9 处既有断言，每处带「原值 / 新值 / 原因」三栏注释，均未削弱：
`window.location.assign(path)` → `<SidebarMenuLink href>` 并追加反向断言；
`onOpenReports` / `useRouter` 改成 doesNotMatch；`SecondaryShell` → `SecondaryHeader`；
导航顺序改在 `NAV_PAGES` 常量里量；两个 render 辅助改为裹 `SidebarProvider`
（provider 上移到 layout）；三处源码路径跟随路由组移动。

测试总数 3391 → 3399，失败清单与基线逐条一致（47 条均为无 Docker 的既有缺口）。

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0193vBv6w5MV2cifdTUu9H5P

frontend/tests/sidebar-state.test.ts

@@ -1,9 +1,12 @@
 import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
 import test from "node:test";
 import {
   defaultSidebarOpen,
+  readStoredSidebarOpen,
   shouldHandleSidebarShortcut,
   sidebarViewportForWidth,
+  writeStoredSidebarOpen,
 } from "../src/lib/sidebar-state.ts";
 import { beginSessionPageLoad, mergeSessionPage } from "../src/lib/session-groups.ts";
 import { homeSurface } from "./home-surface.ts";
@@ -47,3 +50,56 @@ test("loadMoreSessions merges by id and only starts one in-flight request", () =
   assert.deepEqual(merged.map((item) => item.id), ["keep", "next"]);
   assert.equal(merged[0]?.updatedAt, 900);
 });
+
+/* T5 · the collapse state is remembered across pages (TASK-sidebar-unify D5).
+   localStorage, not the shadcn `sidebar_state` cookie: `/`, `/chart` and
+   `/ephemeris` are all static routes, and reading a cookie on the server would
+   opt every one of them out of static rendering. */
+
+function fakeStorage(initial?: string) {
+  let value = initial;
+  return {
+    getItem: () => value ?? null,
+    setItem: (_key: string, next: string) => { value = next; },
+    read: () => value,
+  };
+}
+
+test("a collapsed desktop sidebar is still collapsed after a remount", () => {
+  const storage = fakeStorage();
+
+  writeStoredSidebarOpen("desktop", false, storage);
+  assert.equal(storage.read(), "false");
+
+  // What SidebarProvider resolves on the next page: stored wins over the
+  // breakpoint default, which for desktop would have been `true`.
+  assert.equal(readStoredSidebarOpen("desktop", storage) ?? defaultSidebarOpen("desktop"), false);
+
+  writeStoredSidebarOpen("desktop", true, storage);
+  assert.equal(readStoredSidebarOpen("desktop", storage) ?? defaultSidebarOpen("desktop"), true);
+
+  // Nothing stored, or something unreadable: the breakpoint default stands.
+  const empty = fakeStorage();
+  assert.equal(readStoredSidebarOpen("desktop", empty), null);
+  assert.equal(readStoredSidebarOpen("tablet", fakeStorage("banana")), null);
+  assert.equal(readStoredSidebarOpen("tablet", empty) ?? defaultSidebarOpen("tablet"), false);
+});
+
+test("the mobile drawer is not remembered, read or written", () => {
+  // Reopening a phone drawer on every navigation is not a preference anyone set.
+  const storage = fakeStorage();
+  writeStoredSidebarOpen("mobile", true, storage);
+  assert.equal(storage.read(), undefined);
+  assert.equal(readStoredSidebarOpen("mobile", fakeStorage("true")), null);
+  assert.equal(readStoredSidebarOpen("mobile", fakeStorage("true")) ?? defaultSidebarOpen("mobile"), false);
+
+  // Unavailable storage (private mode, blocked site data) degrades, never throws.
+  assert.equal(readStoredSidebarOpen("desktop", null), null);
+  assert.doesNotThrow(() => writeStoredSidebarOpen("desktop", true, null));
+
+  // And the provider applies it in the same effect that applied the breakpoint
+  // default, so a stored value costs no frame the default did not already cost.
+  const provider = readFileSync(new URL("../src/components/ui/sidebar.tsx", import.meta.url), "utf8");
+  assert.match(provider, /readStoredSidebarOpen\(viewport\) \?\? defaultSidebarOpen\(viewport\)/);
+  assert.match(provider, /writeStoredSidebarOpen\(viewport, nextOpen\)/);
+});