fix(tools): harden scheduler limits and logs

Guard scheduler system actions against pending work, serialize diagnostic log transitions, and keep speed-limit saves truthful after backend failures.\n\nNo linked issue was found for this audit.

src/store/useSettingsStore.test.ts

@@ -0,0 +1,27 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { useSettingsStore } from './useSettingsStore';
+import * as ipc from '../ipc';
+
+vi.mock('../ipc', () => ({
+  invokeCommand: vi.fn()
+}));
+
+vi.mock('../utils/logger', () => ({
+  info: vi.fn()
+}));
+
+describe('useSettingsStore global speed limit persistence', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    useSettingsStore.setState({ globalSpeedLimit: '2M' });
+  });
+
+  it('keeps the saved value when the backend rejects a limit change', async () => {
+    vi.mocked(ipc.invokeCommand).mockRejectedValueOnce(new Error('aria2 unavailable'));
+
+    await expect(useSettingsStore.getState().setGlobalSpeedLimit('3M')).rejects.toThrow('aria2 unavailable');
+
+    expect(useSettingsStore.getState().globalSpeedLimit).toBe('2M');
+    expect(ipc.invokeCommand).toHaveBeenCalledWith('set_global_speed_limit', { limit: '3M' });
+  });
+});

src/store/useSettingsStore.ts

@@ -17,6 +17,7 @@ import {
   DEFAULT_CATEGORY_SUBFOLDERS,
   normalizeDownloadLocationSettings
 } from '../utils/downloadLocations';
+import { normalizeSpeedLimitForBackend } from '../utils/downloads';
 
 let settingsSave = Promise.resolve();
 const DEFAULT_SCHEDULER_QUEUE_ID = '00000000-0000-0000-0000-000000000001';
@@ -165,7 +166,7 @@ export interface SettingsState {
   setBaseDownloadFolder: (path: string) => void;
   approveDownloadRoot: (path: string) => Promise<string>;
   setMaxConcurrentDownloads: (count: number) => void;
-  setGlobalSpeedLimit: (limit: string) => void;
+  setGlobalSpeedLimit: (limit: string) => Promise<void>;
   setSpeedLimitPresetValues: (values: number[]) => void;
   setLogsEnabled: (enabled: boolean) => void;
   setActiveView: (view: ActiveView) => void;
@@ -308,7 +309,10 @@ export const useSettingsStore = create<SettingsState>()(
           maxConcurrentDownloads: clampSettingInteger(max, 1, 12, 3)
         });
       },
-      setGlobalSpeedLimit: (limit) => {
+      setGlobalSpeedLimit: async (limit) => {
+        await invoke('set_global_speed_limit', {
+          limit: normalizeSpeedLimitForBackend(limit)
+        });
         info('Settings updated: globalSpeedLimit');
         set({ globalSpeedLimit: limit });
       },