fix: complete marketplace client remediation

tests/unit/plugin-marketplace-pages.test.tsx

@@ -112,6 +112,35 @@ describe('My Plugins', () => {
     expect(screen.getByText('稳定版 2.0.0')).toBeVisible();
   });
 
+  it('updates an installed Beta package only through the explicit Beta action', () => {
+    const onUpdate = vi.fn();
+    const onInstallBeta = vi.fn();
+    render(<MemoryRouter><MyPluginsView
+      library={{ ...library, items: [library.items[0]] }}
+      installations={{ 'makelore.notes': { status: 'installed', pluginId: 'makelore.notes', channel: 'beta', version: '2.0.0', releaseId: 'beta-1' } }}
+      state="ready" pending={{}} onRefresh={vi.fn()} onInstall={vi.fn()} onUpdate={onUpdate}
+      onInstallBeta={onInstallBeta} onUninstall={vi.fn()} onRemove={vi.fn()} onReacquire={vi.fn()}
+    /></MemoryRouter>);
+
+    expect(screen.queryByRole('button', { name: '更新灵感笔记' })).not.toBeInTheDocument();
+    const updateBeta = screen.getByRole('button', { name: '更新 Beta灵感笔记' });
+    fireEvent.click(updateBeta);
+    expect(onInstallBeta).toHaveBeenCalledWith('makelore.notes');
+    expect(onUpdate).not.toHaveBeenCalled();
+    expect(screen.getByText('当前频道：Beta')).toBeVisible();
+  });
+
+  it('does not silently fall back to stable when the installed Beta channel has no release', () => {
+    render(<MemoryRouter><MyPluginsView
+      library={{ ...library, items: [{ ...library.items[0], betaVersion: null }] }}
+      installations={{ 'makelore.notes': { status: 'installed', pluginId: 'makelore.notes', channel: 'beta', version: '2.0.0', releaseId: 'beta-1' } }}
+      state="ready" pending={{}} onRefresh={vi.fn()} onInstall={vi.fn()} onUpdate={vi.fn()}
+      onInstallBeta={vi.fn()} onUninstall={vi.fn()} onRemove={vi.fn()} onReacquire={vi.fn()}
+    /></MemoryRouter>);
+    expect(screen.getByText('当前 Beta 频道暂无可用版本；不会静默切回稳定版。')).toBeVisible();
+    expect(screen.queryByRole('button', { name: '更新灵感笔记' })).not.toBeInTheDocument();
+  });
+
   it('names signature, yanked/not-ready, and incompatible failures without hiding the old install', () => {
     render(<MemoryRouter><MyPluginsView
       library={{ ...library, items: [library.items[0]] }}