feat: cache soundfont MP3s in OPFS and add cache controls

src/components/settings/sections/GeneralSettings.test.tsx

@@ -12,6 +12,14 @@ const { localSeparatorModelCacheMock } = vi.hoisted(() => ({
   },
 }));
 
+const { soundfontInstrumentCacheMock } = vi.hoisted(() => ({
+  soundfontInstrumentCacheMock: {
+    deleteInstrument: vi.fn().mockResolvedValue(undefined),
+    deleteAll: vi.fn().mockResolvedValue(undefined),
+    getCacheSummary: vi.fn().mockResolvedValue({ instrumentCount: 2, instruments: ['acoustic_grand_piano', 'violin'] }),
+  },
+}));
+
 const configState = new Map<string, unknown>([
   ['general.language', 'auto'],
   ['general.agent_mode', 'regular'],
@@ -90,6 +98,10 @@ vi.mock('../../../util/local-separator/modelCache', () => ({
   LocalSeparatorModelCache: localSeparatorModelCacheMock,
 }));
 
+vi.mock('../../../util/soundfontInstrumentCache', () => ({
+  SoundfontInstrumentCache: soundfontInstrumentCacheMock,
+}));
+
 describe('GeneralSettings', () => {
   const renderSettings = (locale: 'en_us' | 'zh_cn' = 'en_us') => render(
     <I18nContext.Provider
@@ -132,6 +144,10 @@ describe('GeneralSettings', () => {
     localSeparatorModelCacheMock.delete.mockClear();
     localSeparatorModelCacheMock.exists.mockClear();
     localSeparatorModelCacheMock.exists.mockResolvedValue(true);
+    soundfontInstrumentCacheMock.deleteAll.mockClear();
+    soundfontInstrumentCacheMock.deleteInstrument.mockClear();
+    soundfontInstrumentCacheMock.getCacheSummary.mockClear();
+    soundfontInstrumentCacheMock.getCacheSummary.mockResolvedValue({ instrumentCount: 2, instruments: ['acoustic_grand_piano', 'violin'] });
   });
 
   it('renders the local context length selector and VRAM hint', async () => {
@@ -338,4 +354,50 @@ describe('GeneralSettings', () => {
       expect(configManagerMock.set).toHaveBeenCalledWith('general.language', 'fr_fr');
     });
   });
+
+  it('renders the soundfont cache status and deletes all cached soundfonts', async () => {
+    soundfontInstrumentCacheMock.getCacheSummary
+      .mockResolvedValueOnce({ instrumentCount: 2, instruments: ['acoustic_grand_piano', 'violin'] })
+      .mockResolvedValueOnce({ instrumentCount: 0, instruments: [] });
+
+    renderSettings();
+
+    expect(await screen.findByText('Soundfont Settings')).toBeTruthy();
+    expect(screen.getByText('2 instruments cached in browser storage.')).toBeTruthy();
+
+    const soundfontDeleteButton = screen.getByRole('button', { name: 'Delete Soundfont Cache' });
+    expect(soundfontDeleteButton).not.toBeDisabled();
+    fireEvent.click(soundfontDeleteButton);
+
+    await waitFor(() => {
+      expect(soundfontInstrumentCacheMock.deleteAll).toHaveBeenCalledOnce();
+    });
+
+    await waitFor(() => {
+      expect(screen.getByText('No cached instruments yet.')).toBeTruthy();
+    });
+  });
+
+  it('deletes the selected cached soundfont instrument', async () => {
+    soundfontInstrumentCacheMock.getCacheSummary
+      .mockResolvedValueOnce({ instrumentCount: 2, instruments: ['acoustic_grand_piano', 'violin'] })
+      .mockResolvedValueOnce({ instrumentCount: 1, instruments: ['acoustic_grand_piano'] });
+
+    renderSettings();
+
+    const select = await screen.findByLabelText('Cached Instrument');
+    fireEvent.change(select, { target: { value: 'violin' } });
+
+    const deleteSelectedButton = screen.getByRole('button', { name: 'Delete Selected Instrument Cache' });
+    expect(deleteSelectedButton).not.toBeDisabled();
+    fireEvent.click(deleteSelectedButton);
+
+    await waitFor(() => {
+      expect(soundfontInstrumentCacheMock.deleteInstrument).toHaveBeenCalledWith('violin');
+    });
+
+    await waitFor(() => {
+      expect(screen.getByText('1 instruments cached in browser storage.')).toBeTruthy();
+    });
+  });
 });

src/components/settings/sections/GeneralSettings.tsx

@@ -2,6 +2,7 @@ import React, { useState, useEffect, useCallback, useMemo } from 'react';
 import { ConfigManager } from '../../../core/config/ConfigManager';
 import { LocalLLMModelManager, type LocalLLMModelState } from '../../../util/localLLMModelManager';
 import { LocalSeparatorModelCache } from '../../../util/local-separator/modelCache';
+import { SoundfontInstrumentCache, type SoundfontCacheSummary } from '../../../util/soundfontInstrumentCache';
 import { useI18n } from '../../../i18n/useI18n';
 import type { LanguageSetting } from '../../../i18n/types';
 import {
@@ -58,6 +59,11 @@ const GeneralSettings: React.FC = () => {
   const [kgoneBaseUrl, setKgoneBaseUrl] = useState<string>('');
   const [kgoneServerManaged, setKgoneServerManaged] = useState<boolean>(false);
   const [soundfontServerManaged, setSoundfontServerManaged] = useState<boolean>(false);
+  const [soundfontCacheSummary, setSoundfontCacheSummary] = useState<SoundfontCacheSummary>({ instrumentCount: 0, instruments: [] });
+  const [isCheckingSoundfontCache, setIsCheckingSoundfontCache] = useState<boolean>(false);
+  const [isDeletingSoundfontCache, setIsDeletingSoundfontCache] = useState<boolean>(false);
+  const [selectedCachedSoundfontInstrument, setSelectedCachedSoundfontInstrument] = useState<string>('');
+  const [isDeletingCachedSoundfontInstrument, setIsDeletingCachedSoundfontInstrument] = useState<boolean>(false);
   const [localContextLength, setLocalContextLength] = useState<LocalLLMContextLength>(LOCAL_LLM_DEFAULT_CONTEXT_LENGTH);
   const [localModelState, setLocalModelState] = useState<LocalLLMModelState>(LocalLLMModelManager.getState());
   const [localModelUrl, setLocalModelUrl] = useState<string>('');
@@ -103,6 +109,35 @@ const GeneralSettings: React.FC = () => {
     }
   }, []);
 
+  const refreshSoundfontCacheState = useCallback(async () => {
+    setIsCheckingSoundfontCache(true);
+    try {
+      const currentBaseUrl = ((configManager.get('general.soundfont.base_url') as string) || '').trim();
+      if (!currentBaseUrl) {
+        setSoundfontCacheSummary({ instrumentCount: 0, instruments: [] });
+        return;
+      }
+
+      const summary = await SoundfontInstrumentCache.getCacheSummary(currentBaseUrl);
+      setSoundfontCacheSummary(summary);
+      setSelectedCachedSoundfontInstrument((currentSelection) => {
+        if (summary.instruments.length === 0) {
+          return '';
+        }
+        if (currentSelection && summary.instruments.includes(currentSelection)) {
+          return currentSelection;
+        }
+        return summary.instruments[0];
+      });
+    } catch (error) {
+      console.error('Failed to check soundfont cache state:', error);
+      setSoundfontCacheSummary({ instrumentCount: 0, instruments: [] });
+      setSelectedCachedSoundfontInstrument('');
+    } finally {
+      setIsCheckingSoundfontCache(false);
+    }
+  }, [configManager]);
+
   // Load configuration values on component mount
   useEffect(() => {
     const loadConfig = async () => {
@@ -150,8 +185,9 @@ const GeneralSettings: React.FC = () => {
     loadConfig();
     const unsubscribe = LocalLLMModelManager.subscribe(setLocalModelState);
     void refreshUvr5ModelCacheState();
+    void refreshSoundfontCacheState();
     return unsubscribe;
-  }, [configManager, refreshUvr5ModelCacheState]);
+  }, [configManager, refreshSoundfontCacheState, refreshUvr5ModelCacheState]);
 
   // Debounced save function for text inputs
   const debouncedSave = useCallback((key: string, value: string) => {
@@ -359,6 +395,35 @@ const GeneralSettings: React.FC = () => {
     }
   };
 
+  const handleDeleteSoundfontCache = async () => {
+    setIsDeletingSoundfontCache(true);
+    try {
+      await SoundfontInstrumentCache.deleteAll();
+      setSoundfontCacheSummary({ instrumentCount: 0, instruments: [] });
+    } catch (error) {
+      console.error('Failed to delete soundfont cache:', error);
+    } finally {
+      setIsDeletingSoundfontCache(false);
+      await refreshSoundfontCacheState();
+    }
+  };
+
+  const handleDeleteCachedSoundfontInstrument = async () => {
+    if (!selectedCachedSoundfontInstrument) {
+      return;
+    }
+
+    setIsDeletingCachedSoundfontInstrument(true);
+    try {
+      await SoundfontInstrumentCache.deleteInstrument(selectedCachedSoundfontInstrument);
+    } catch (error) {
+      console.error(`Failed to delete soundfont cache for ${selectedCachedSoundfontInstrument}:`, error);
+    } finally {
+      setIsDeletingCachedSoundfontInstrument(false);
+      await refreshSoundfontCacheState();
+    }
+  };
+
   const handleLocalContextLengthChange = async (value: string) => {
     const parsed = Number(value);
     const normalized = normalizeLocalLLMContextLength(parsed);
@@ -998,6 +1063,75 @@ const GeneralSettings: React.FC = () => {
               </a>
             </div>
           </div>
+
+          <div className="settings-item">
+            <label className="settings-label">
+              {t('settings.general.soundfont.cachedStatus')}
+            </label>
+            <div className="settings-help" style={{ fontSize: '12px', color: '#888', marginTop: '4px' }}>
+              {isCheckingSoundfontCache
+                ? t('settings.general.soundfont.cacheChecking')
+                : soundfontCacheSummary.instrumentCount > 0
+                  ? t('settings.general.soundfont.cacheReady', { count: soundfontCacheSummary.instrumentCount })
+                  : t('settings.general.soundfont.cacheEmpty')}
+            </div>
+            <div className="settings-help" style={{ fontSize: '12px', color: '#888', marginTop: '4px' }}>
+              {t('settings.general.soundfont.cacheHelp')}
+            </div>
+          </div>
+
+          <div className="settings-item">
+            <label className="settings-label" htmlFor="soundfont-cached-instrument-select">
+              {t('settings.general.soundfont.cachedInstrument')}
+            </label>
+            <select
+              id="soundfont-cached-instrument-select"
+              className="settings-select"
+              value={selectedCachedSoundfontInstrument}
+              onChange={(e) => setSelectedCachedSoundfontInstrument(e.target.value)}
+              disabled={isCheckingSoundfontCache || soundfontCacheSummary.instrumentCount === 0 || isDeletingCachedSoundfontInstrument}
+            >
+              {soundfontCacheSummary.instrumentCount === 0 ? (
+                <option value="">{t('settings.general.soundfont.noCachedInstrumentOption')}</option>
+              ) : (
+                soundfontCacheSummary.instruments.map((instrumentName) => (
+                  <option key={instrumentName} value={instrumentName}>
+                    {instrumentName}
+                  </option>
+                ))
+              )}
+            </select>
+            <div className="settings-help" style={{ fontSize: '12px', color: '#888', marginTop: '4px' }}>
+              {t('settings.general.soundfont.cachedInstrumentHelp')}
+            </div>
+          </div>
+
+          <div className="settings-item" style={{ marginTop: '12px' }}>
+            <div style={{ display: 'flex', gap: '8px', flexWrap: 'wrap' }}>
+              <button
+                type="button"
+                className="settings-btn settings-btn-danger"
+                onClick={() => void handleDeleteCachedSoundfontInstrument()}
+                disabled={
+                  isDeletingCachedSoundfontInstrument
+                  || isCheckingSoundfontCache
+                  || !selectedCachedSoundfontInstrument
+                  || soundfontCacheSummary.instrumentCount === 0
+                }
+              >
+                {isDeletingCachedSoundfontInstrument ? t('settings.deleting') : t('settings.general.soundfont.deleteSelectedCache')}
+              </button>
+
+              <button
+                type="button"
+                className="settings-btn settings-btn-danger"
+                onClick={() => void handleDeleteSoundfontCache()}
+                disabled={isDeletingSoundfontCache || isCheckingSoundfontCache || soundfontCacheSummary.instrumentCount === 0}
+              >
+                {isDeletingSoundfontCache ? t('settings.deleting') : t('settings.general.soundfont.deleteCache')}
+              </button>
+            </div>
+          </div>
         </div>
 
         <div className="settings-group">

src/core/audio-interface/KGToneBuffersPool.test.ts

@@ -0,0 +1,188 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+
+const {
+  toneAudioBuffersCtorMock,
+  existsMock,
+  getInstrumentObjectUrlsMock,
+  storeInstrumentMock,
+  deleteInstrumentMock,
+  configGetMock,
+} = vi.hoisted(() => ({
+  toneAudioBuffersCtorMock: vi.fn(),
+  existsMock: vi.fn(),
+  getInstrumentObjectUrlsMock: vi.fn(),
+  storeInstrumentMock: vi.fn(),
+  deleteInstrumentMock: vi.fn(),
+  configGetMock: vi.fn(),
+}));
+
+vi.mock('../../constants/generalMidiConstants', () => ({
+  FLUIDR3_INSTRUMENT_MAP: {
+    test_instrument: {
+      displayName: 'Test Instrument',
+      midiInstrument: 1,
+      image: 'test.png',
+      group: 'TEST',
+      pitchRange: [60, 61],
+    },
+  },
+}));
+
+vi.mock('../config/ConfigManager', () => ({
+  ConfigManager: {
+    instance: () => ({
+      getIsInitialized: () => true,
+      initialize: vi.fn().mockResolvedValue(undefined),
+      get: configGetMock,
+    }),
+  },
+}));
+
+vi.mock('../../util/soundfontInstrumentCache', () => ({
+  SoundfontInstrumentCache: {
+    exists: existsMock,
+    getInstrumentObjectUrls: getInstrumentObjectUrlsMock,
+    storeInstrument: storeInstrumentMock,
+    deleteInstrument: deleteInstrumentMock,
+  },
+}));
+
+vi.mock('tone', () => ({
+  ToneAudioBuffers: toneAudioBuffersCtorMock,
+}));
+
+import { KGToneBuffersPool } from './KGToneBuffersPool';
+
+describe('KGToneBuffersPool soundfont cache behavior', () => {
+  beforeEach(() => {
+    vi.clearAllMocks();
+    configGetMock.mockReturnValue('https://cdn.example.com/FluidR3_GM/');
+    existsMock.mockResolvedValue(false);
+    getInstrumentObjectUrlsMock.mockResolvedValue({
+      C4: 'blob:cached-c4',
+      Db4: 'blob:cached-db4',
+    });
+    storeInstrumentMock.mockResolvedValue(undefined);
+    deleteInstrumentMock.mockResolvedValue(undefined);
+
+    toneAudioBuffersCtorMock.mockImplementation((options: {
+      urls: Record<string, string>;
+      onload: () => void;
+      onerror?: (error: Error) => void;
+    }) => {
+      const buffers = {
+        loaded: true,
+        has: (key: string) => key in options.urls,
+        get: (key: string) => ({ key, duration: 1, loaded: true }),
+        dispose: vi.fn(),
+      };
+      queueMicrotask(() => options.onload());
+      return buffers;
+    });
+
+    vi.stubGlobal('fetch', vi.fn(async (url: string) => {
+      if (url.includes('Db4') && url.includes('fail-db4')) {
+        return new Response(null, { status: 500 });
+      }
+      return new Response(new Uint8Array([1, 2, 3]), { status: 200 });
+    }));
+    vi.stubGlobal('URL', {
+      createObjectURL: vi.fn((blob: Blob) => `blob:${blob.size}:${Math.random()}`),
+      revokeObjectURL: vi.fn(),
+    });
+
+    KGToneBuffersPool.instance().dispose();
+    (KGToneBuffersPool as unknown as { _instance: KGToneBuffersPool | null })._instance = null;
+  });
+
+  it('loads from OPFS cache without refetching remote URLs', async () => {
+    existsMock.mockResolvedValue(true);
+
+    const pool = KGToneBuffersPool.instance();
+    const buffers = await pool.getToneAudioBuffers('test_instrument');
+
+    expect(buffers.loaded).toBe(true);
+    expect(getInstrumentObjectUrlsMock).toHaveBeenCalledOnce();
+    expect(fetch).not.toHaveBeenCalled();
+  });
+
+  it('stores a complete remote instrument and reuses the in-memory cache', async () => {
+    const pool = KGToneBuffersPool.instance();
+
+    await pool.getToneAudioBuffers('test_instrument');
+    await pool.getToneAudioBuffers('test_instrument');
+
+    expect(fetch).toHaveBeenCalledTimes(2);
+    expect(storeInstrumentMock).toHaveBeenCalledOnce();
+    expect(toneAudioBuffersCtorMock).toHaveBeenCalledOnce();
+  });
+
+  it('does not persist or memoize a partial remote load', async () => {
+    configGetMock.mockReturnValue('https://fail-db4.example.com/FluidR3_GM/');
+    vi.stubGlobal('fetch', vi.fn(async (url: string) => {
+      if (url.includes('Db4')) {
+        return new Response(null, { status: 500 });
+      }
+      return new Response(new Uint8Array([1, 2, 3]), { status: 200 });
+    }));
+
+    const pool = KGToneBuffersPool.instance();
+    const first = await pool.getToneAudioBuffers('test_instrument');
+    const second = await pool.getToneAudioBuffers('test_instrument');
+
+    expect(first.loaded).toBe(true);
+    expect(second.loaded).toBe(true);
+    expect(fetch).toHaveBeenCalledTimes(4);
+    expect(storeInstrumentMock).not.toHaveBeenCalled();
+    expect(deleteInstrumentMock).toHaveBeenCalled();
+  });
+
+  it('retries remote loading after a previous partial success', async () => {
+    let requestCount = 0;
+    vi.stubGlobal('fetch', vi.fn(async (url: string) => {
+      requestCount += 1;
+      if (requestCount <= 2 && url.includes('Db4')) {
+        return new Response(null, { status: 500 });
+      }
+      return new Response(new Uint8Array([1, 2, 3]), { status: 200 });
+    }));
+
+    const pool = KGToneBuffersPool.instance();
+    await pool.getToneAudioBuffers('test_instrument');
+    await pool.getToneAudioBuffers('test_instrument');
+
+    expect(fetch).toHaveBeenCalledTimes(4);
+    expect(storeInstrumentMock).toHaveBeenCalledOnce();
+  });
+
+  it('deduplicates concurrent loads for the same instrument', async () => {
+    let onloadCount = 0;
+    toneAudioBuffersCtorMock.mockImplementation((options: {
+      urls: Record<string, string>;
+      onload: () => void;
+    }) => {
+      const buffers = {
+        loaded: true,
+        has: (key: string) => key in options.urls,
+        get: (key: string) => ({ key, duration: 1, loaded: true }),
+        dispose: vi.fn(),
+      };
+      setTimeout(() => {
+        onloadCount += 1;
+        options.onload();
+      }, 0);
+      return buffers;
+    });
+
+    const pool = KGToneBuffersPool.instance();
+    const [first, second] = await Promise.all([
+      pool.getToneAudioBuffers('test_instrument'),
+      pool.getToneAudioBuffers('test_instrument'),
+    ]);
+
+    expect(first).toBe(second);
+    expect(fetch).toHaveBeenCalledTimes(2);
+    expect(toneAudioBuffersCtorMock).toHaveBeenCalledOnce();
+    expect(onloadCount).toBe(1);
+  });
+});

src/core/audio-interface/KGToneBuffersPool.ts

@@ -1,8 +1,14 @@
 import { SAMPLER_CONSTANTS } from '../../constants/coreConstants';
 import { FLUIDR3_INSTRUMENT_MAP } from '../../constants/generalMidiConstants';
 import { ConfigManager } from '../config/ConfigManager';
+import { SoundfontInstrumentCache } from '../../util/soundfontInstrumentCache';
 import * as Tone from 'tone';
 
+interface ToneBufferLoadResult {
+  buffers: Tone.ToneAudioBuffers;
+  cacheInMemory: boolean;
+}
+
 /**
  * KGToneBuffersPool - Singleton class for managing ToneAudioBuffers
  * Handles loading and caching of soundfont audio buffers for instruments
@@ -20,6 +26,8 @@ export class KGToneBuffersPool {
   // Simple event listeners for load start/end without coupling to UI layer
   private loadingListeners: Array<(_evt: { type: 'start' | 'end'; instrument: string }) => void> = [];
 
+  private activeBaseUrl: string | null = null;
+
   // Private constructor to prevent direct instantiation
   private constructor() {
     console.log("KGToneBuffersPool initialized");
@@ -67,6 +75,9 @@ export class KGToneBuffersPool {
    * Handles race conditions by ensuring only one loading operation per instrument
    */
   public async getToneAudioBuffers(name: string): Promise<Tone.ToneAudioBuffers> {
+    const baseUrl = await this.getSoundfontBaseUrl();
+    this.ensureMemoryCacheMatchesBaseUrl(baseUrl);
+
     // Check if already fully loaded and cached
     const cachedBuffers = this.bufferMap.get(name);
     if (cachedBuffers && cachedBuffers.loaded) {
@@ -82,18 +93,22 @@ export class KGToneBuffersPool {
 
     // Start new loading operation
     console.log(`KGToneBuffersPool: Starting new loading operation for ${name}`);
-    const loadingPromise = this.createToneAudioBuffers(name);
-    this.loadingPromises.set(name, loadingPromise);
+    const loadingPromise = this.createToneAudioBuffers(name, baseUrl);
+    this.loadingPromises.set(name, loadingPromise.then(result => result.buffers));
     // Emit start AFTER registering the promise to avoid duplicate start events in races
     this.emitLoadingEvent({ type: 'start', instrument: name });
     console.log(`[KGToneBuffersPool] start: Active load count: ${this.getActiveLoadCount()}`);
 
     try {
-      const buffers = await loadingPromise;
+      const result = await loadingPromise;
+      const buffers = result.buffers;
 
-      // Cache the fully loaded buffers
-      this.bufferMap.set(name, buffers);
-      console.log(`KGToneBuffersPool: Cached loaded buffers for ${name}`);
+      if (result.cacheInMemory) {
+        this.bufferMap.set(name, buffers);
+        console.log(`KGToneBuffersPool: Cached loaded buffers for ${name}`);
+      } else {
+        console.log(`KGToneBuffersPool: Skipping in-memory cache for ${name} due to partial soundfont load`);
+      }
 
       // Remove from loading promises since it's complete
       this.loadingPromises.delete(name);
@@ -115,43 +130,63 @@ export class KGToneBuffersPool {
   /**
    * Create ToneAudioBuffers for an instrument
    */
-  private async createToneAudioBuffers(name: string): Promise<Tone.ToneAudioBuffers> {
-    const configManager = ConfigManager.instance();
-    if (!configManager.getIsInitialized()) {
-      await configManager.initialize();
+  private async createToneAudioBuffers(name: string, baseUrl: string): Promise<ToneBufferLoadResult> {
+    const instrumentName = name;
+
+    if (!instrumentName) {
+      throw new Error(`Unknown instrument: ${name}`);
     }
 
-    return new Promise((resolve, reject) => {
-      try {
-        const instrumentName = name;
+    const keyNames = this.getInstrumentKeyNames(instrumentName);
 
-        if (!instrumentName) {
-          throw new Error(`Unknown instrument: ${name}`);
+    try {
+      if (await SoundfontInstrumentCache.exists(instrumentName, keyNames, baseUrl)) {
+        console.log(`Loading ToneAudioBuffers for ${name} from OPFS cache...`);
+        const cachedUrls = await SoundfontInstrumentCache.getInstrumentObjectUrls(instrumentName, keyNames, baseUrl);
+        try {
+          const buffers = await this.loadToneAudioBuffers(cachedUrls, name);
+          return { buffers, cacheInMemory: true };
+        } catch (error) {
+          console.warn(`Cached soundfont load failed for ${name}, deleting cache and retrying remote download.`, error);
+          this.revokeObjectUrls(cachedUrls);
+          await SoundfontInstrumentCache.deleteInstrument(instrumentName);
         }
-
-        const baseUrl = (ConfigManager.instance().get('general.soundfont.base_url') as string)
-          || SAMPLER_CONSTANTS.TONE_SAMPLERS.FLUID.url;
-
-        const urls = this.generateKeyUrls(baseUrl, instrumentName);
-
-        console.log(`Loading ToneAudioBuffers for ${name} (${instrumentName})...`);
-
-        // Create ToneAudioBuffers with onload callback
-        const buffers = new Tone.ToneAudioBuffers(
-          urls,
-          () => {
-            console.log(`ToneAudioBuffers loaded successfully for ${name}`);
-            resolve(buffers);
-          }
-        );
-
-        // Don't cache until loading is complete - this will be handled in getToneAudioBuffers
-
-      } catch (error) {
-        console.error(`Error creating ToneAudioBuffers for ${name}:`, error);
-        reject(error);
       }
-    });
+
+      console.log(`Loading ToneAudioBuffers for ${name} (${instrumentName}) from remote source...`);
+      const remoteUrls = this.generateKeyUrls(baseUrl, instrumentName);
+      const fetchResults = await this.fetchRemoteInstrumentBlobs(remoteUrls);
+      const successfulKeys = Object.keys(fetchResults.successfulBlobs);
+
+      if (successfulKeys.length === 0) {
+        throw new Error(`Failed to load any soundfont samples for ${instrumentName}`);
+      }
+
+      const loadUrls = Object.fromEntries(
+        successfulKeys.map(key => [key, URL.createObjectURL(fetchResults.successfulBlobs[key])]),
+      ) as Record<string, string>;
+
+      const buffers = await this.loadToneAudioBuffers(loadUrls, name);
+
+      if (fetchResults.failures.length === 0) {
+        try {
+          await SoundfontInstrumentCache.storeInstrument(instrumentName, keyNames, fetchResults.successfulBlobs, baseUrl);
+        } catch (error) {
+          console.warn(`Failed to persist soundfont cache for ${instrumentName}:`, error);
+        }
+      } else {
+        console.warn(`Skipping cache finalize for ${instrumentName} because ${fetchResults.failures.length} pitch samples failed to load.`);
+        await SoundfontInstrumentCache.deleteInstrument(instrumentName);
+      }
+
+      return {
+        buffers,
+        cacheInMemory: fetchResults.failures.length === 0,
+      };
+    } catch (error) {
+      console.error(`Error creating ToneAudioBuffers for ${name}:`, error);
+      throw error;
+    }
   }
 
   /**
@@ -161,21 +196,7 @@ export class KGToneBuffersPool {
   private generateKeyUrls(baseUrl: string, instrumentName: string): { [key: string]: string } {
     const urls: { [key: string]: string } = {};
 
-    // get the range of the instrument. 
-    // TODO: make the sound library name configurable.
-    const range = FLUIDR3_INSTRUMENT_MAP[instrumentName]?.pitchRange || [21, 108];
-
-    // Note names in order (using flats instead of sharps where applicable)
-    const noteNames = ['C', 'Db', 'D', 'Eb', 'E', 'F', 'Gb', 'G', 'Ab', 'A', 'Bb', 'B'];
-
-    // Generate keys from A0 to C8 (MIDI notes 21 to 108)
-    for (let midiNote = range[0]; midiNote <= range[1]; midiNote++) {
-      const octave = Math.floor((midiNote - 12) / 12);
-      const noteIndex = (midiNote - 12) % 12;
-      const noteName = noteNames[noteIndex];
-      const keyName = `${noteName}${octave}`;
-
-      // Generate URL for this key
+    for (const keyName of this.getInstrumentKeyNames(instrumentName)) {
       urls[keyName] = `${baseUrl}${instrumentName}-mp3/${keyName}.mp3`;
     }
 
@@ -184,6 +205,121 @@ export class KGToneBuffersPool {
     return urls;
   }
 
+  private getInstrumentKeyNames(instrumentName: string): string[] {
+    const range = FLUIDR3_INSTRUMENT_MAP[instrumentName]?.pitchRange || [21, 108];
+    const noteNames = ['C', 'Db', 'D', 'Eb', 'E', 'F', 'Gb', 'G', 'Ab', 'A', 'Bb', 'B'];
+    const keys: string[] = [];
+
+    for (let midiNote = range[0]; midiNote <= range[1]; midiNote++) {
+      const octave = Math.floor((midiNote - 12) / 12);
+      const noteIndex = (midiNote - 12) % 12;
+      const noteName = noteNames[noteIndex];
+      keys.push(`${noteName}${octave}`);
+    }
+
+    return keys;
+  }
+
+  private async fetchRemoteInstrumentBlobs(urls: Record<string, string>): Promise<{
+    successfulBlobs: Record<string, Blob>;
+    failures: string[];
+  }> {
+    const entries = Object.entries(urls);
+    const successfulBlobs: Record<string, Blob> = {};
+    const failures: string[] = [];
+
+    await Promise.all(entries.map(async ([key, url]) => {
+      try {
+        const response = await this.fetchWithTimeout(url, 10000);
+        if (!response.ok) {
+          throw new Error(`HTTP ${response.status}`);
+        }
+
+        successfulBlobs[key] = await response.blob();
+      } catch (error) {
+        console.warn(`Failed to fetch soundfont sample ${key}:`, error);
+        failures.push(key);
+      }
+    }));
+
+    return { successfulBlobs, failures };
+  }
+
+  private async fetchWithTimeout(url: string, timeoutMs: number): Promise<Response> {
+    const controller = new AbortController();
+    const timeout = window.setTimeout(() => controller.abort(), timeoutMs);
+
+    try {
+      return await fetch(url, { signal: controller.signal });
+    } finally {
+      clearTimeout(timeout);
+    }
+  }
+
+  private loadToneAudioBuffers(urls: Record<string, string>, name: string): Promise<Tone.ToneAudioBuffers> {
+    return new Promise((resolve, reject) => {
+      if (Object.keys(urls).length === 0) {
+        reject(new Error(`No audio sources were available for ${name}`));
+        return;
+      }
+
+      let settled = false;
+      const cleanup = () => this.revokeObjectUrls(urls);
+
+      const buffers = new Tone.ToneAudioBuffers({
+        urls,
+        onload: () => {
+          if (settled) return;
+          settled = true;
+          cleanup();
+          console.log(`ToneAudioBuffers loaded successfully for ${name}`);
+          resolve(buffers);
+        },
+        onerror: (error) => {
+          if (settled) return;
+          settled = true;
+          cleanup();
+          reject(error);
+        },
+      });
+    });
+  }
+
+  private revokeObjectUrls(urls: Record<string, string>): void {
+    Object.values(urls).forEach(url => {
+      if (url.startsWith('blob:')) {
+        URL.revokeObjectURL(url);
+      }
+    });
+  }
+
+  private async getSoundfontBaseUrl(): Promise<string> {
+    const configManager = ConfigManager.instance();
+    if (!configManager.getIsInitialized()) {
+      await configManager.initialize();
+    }
+
+    return (configManager.get('general.soundfont.base_url') as string)
+      || SAMPLER_CONSTANTS.TONE_SAMPLERS.FLUID.url;
+  }
+
+  private ensureMemoryCacheMatchesBaseUrl(baseUrl: string): void {
+    if (this.activeBaseUrl === baseUrl) {
+      return;
+    }
+
+    this.activeBaseUrl = baseUrl;
+    this.bufferMap.forEach((buffers, name) => {
+      try {
+        buffers.dispose();
+        console.log(`Disposed ToneAudioBuffers for ${name} due to soundfont base URL change`);
+      } catch (error) {
+        console.error(`Error disposing ToneAudioBuffers for ${name} during soundfont base URL change:`, error);
+      }
+    });
+    this.bufferMap.clear();
+  }
+
   /**
    * Clear all cached buffers and dispose of resources
    */

src/i18n/messages/en_us.ts

@@ -97,6 +97,16 @@ export const enUsMessages: TranslationMessages = {
   'settings.general.soundfont.managed': 'Soundfont configuration is managed by the server (kgone-server.json). Settings are read-only.',
   'settings.general.soundfont.baseUrl': 'Base URL',
   'settings.general.soundfont.baseUrlHelp': 'Changing this URL to an incompatible soundfont source may cause some instruments to sound wrong or not play.',
+  'settings.general.soundfont.cachedStatus': 'Cached Soundfont Status',
+  'settings.general.soundfont.cacheChecking': 'Checking soundfont cache...',
+  'settings.general.soundfont.cacheReady': '{count} instruments cached in browser storage.',
+  'settings.general.soundfont.cacheEmpty': 'No cached instruments yet.',
+  'settings.general.soundfont.cacheHelp': 'Cached instruments are stored in browser OPFS and reused for future instrument loads until you change the base URL or delete the cache.',
+  'settings.general.soundfont.cachedInstrument': 'Cached Instrument',
+  'settings.general.soundfont.cachedInstrumentHelp': 'Choose a cached instrument to delete only that instrument’s local soundfont files.',
+  'settings.general.soundfont.noCachedInstrumentOption': 'No cached instruments',
+  'settings.general.soundfont.deleteSelectedCache': 'Delete Selected Instrument Cache',
+  'settings.general.soundfont.deleteCache': 'Delete Soundfont Cache',
   'settings.general.kgone.section': 'K.G.One Settings',
   'settings.general.kgone.managed': 'K.G.One configuration is managed by the server (kgone-server.json). Settings are read-only.',
   'settings.general.kgone.enabled': 'Enable K.G.One Integration',

src/i18n/messages/fr_fr.ts

@@ -94,6 +94,16 @@ export const frFrMessages: TranslationMessages = {
   'settings.general.soundfont.managed': 'La configuration des soundfonts est gérée par le serveur (kgone-server.json). Ces réglages sont en lecture seule.',
   'settings.general.soundfont.baseUrl': 'URL de base',
   'settings.general.soundfont.baseUrlHelp': 'Une source de soundfont incompatible peut provoquer des timbres incorrects ou empêcher certains instruments de jouer.',
+  'settings.general.soundfont.cachedStatus': 'État du cache des soundfonts',
+  'settings.general.soundfont.cacheChecking': 'Vérification du cache des soundfonts...',
+  'settings.general.soundfont.cacheReady': '{count} instruments en cache dans le navigateur.',
+  'settings.general.soundfont.cacheEmpty': 'Aucun instrument en cache pour le moment.',
+  'settings.general.soundfont.cacheHelp': 'Les instruments en cache sont stockés dans l’OPFS du navigateur et réutilisés lors des prochains chargements jusqu’à un changement d’URL de base ou une suppression du cache.',
+  'settings.general.soundfont.cachedInstrument': 'Instrument en cache',
+  'settings.general.soundfont.cachedInstrumentHelp': 'Choisissez un instrument en cache pour supprimer uniquement ses fichiers soundfont locaux.',
+  'settings.general.soundfont.noCachedInstrumentOption': 'Aucun instrument en cache',
+  'settings.general.soundfont.deleteSelectedCache': 'Supprimer le cache de l’instrument sélectionné',
+  'settings.general.soundfont.deleteCache': 'Supprimer le cache des soundfonts',
   'settings.general.kgone.section': 'Réglages K.G.One',
   'settings.general.kgone.managed': 'La configuration K.G.One est gérée par le serveur (kgone-server.json). Ces réglages sont en lecture seule.',
   'settings.general.kgone.enabled': 'Activer l\'intégration K.G.One',

src/i18n/messages/zh_cn.ts

@@ -95,6 +95,16 @@ export const zhCnMessages: TranslationMessages = {
   'settings.general.soundfont.managed': 'Soundfont 配置由服务器（kgone-server.json）管理，当前设置为只读。',
   'settings.general.soundfont.baseUrl': '基础 URL',
   'settings.general.soundfont.baseUrlHelp': '如果改成不兼容的 soundfont 源，某些乐器可能发声错误或无法播放。',
+  'settings.general.soundfont.cachedStatus': 'Soundfont 缓存状态',
+  'settings.general.soundfont.cacheChecking': '正在检查 soundfont 缓存...',
+  'settings.general.soundfont.cacheReady': '浏览器存储中已缓存 {count} 个乐器。',
+  'settings.general.soundfont.cacheEmpty': '当前还没有已缓存的乐器。',
+  'settings.general.soundfont.cacheHelp': '已缓存的乐器会保存在浏览器 OPFS 中，后续加载时会复用；更改基础 URL 或删除缓存后将重新下载。',
+  'settings.general.soundfont.cachedInstrument': '已缓存乐器',
+  'settings.general.soundfont.cachedInstrumentHelp': '选择一个已缓存乐器，只删除该乐器的本地 soundfont 文件。',
+  'settings.general.soundfont.noCachedInstrumentOption': '没有已缓存的乐器',
+  'settings.general.soundfont.deleteSelectedCache': '删除所选乐器缓存',
+  'settings.general.soundfont.deleteCache': '删除 Soundfont 缓存',
   'settings.general.kgone.section': 'K.G.One 设置',
   'settings.general.kgone.managed': 'K.G.One 配置由服务器（kgone-server.json）管理，当前设置为只读。',
   'settings.general.kgone.enabled': '启用 K.G.One 集成',

src/i18n/messages/zh_hk.ts

@@ -95,6 +95,16 @@ export const zhHkMessages: TranslationMessages = {
   'settings.general.soundfont.managed': 'Soundfont 設定由伺服器（kgone-server.json）管理，目前設定為唯讀。',
   'settings.general.soundfont.baseUrl': '基礎 URL',
   'settings.general.soundfont.baseUrlHelp': '如果改成不兼容的 soundfont 源，某些樂器可能發聲錯誤或無法播放。',
+  'settings.general.soundfont.cachedStatus': 'Soundfont 快取狀態',
+  'settings.general.soundfont.cacheChecking': '正在檢查 soundfont 快取...',
+  'settings.general.soundfont.cacheReady': '瀏覽器儲存空間中已快取 {count} 個樂器。',
+  'settings.general.soundfont.cacheEmpty': '目前還沒有已快取的樂器。',
+  'settings.general.soundfont.cacheHelp': '已快取的樂器會保存在瀏覽器 OPFS 中，後續載入時會重用；更改基礎 URL 或刪除快取後將重新下載。',
+  'settings.general.soundfont.cachedInstrument': '已快取樂器',
+  'settings.general.soundfont.cachedInstrumentHelp': '選擇一個已快取樂器，只刪除該樂器的本地 soundfont 檔案。',
+  'settings.general.soundfont.noCachedInstrumentOption': '沒有已快取的樂器',
+  'settings.general.soundfont.deleteSelectedCache': '刪除所選樂器快取',
+  'settings.general.soundfont.deleteCache': '刪除 Soundfont 快取',
   'settings.general.kgone.section': 'K.G.One 設定',
   'settings.general.kgone.managed': 'K.G.One 設定由伺服器（kgone-server.json）管理，目前設定為唯讀。',
   'settings.general.kgone.enabled': '啟用 K.G.One 集成',

src/util/soundfontInstrumentCache.test.ts

@@ -0,0 +1,199 @@
+import { beforeEach, describe, expect, it, vi } from 'vitest';
+import { SoundfontInstrumentCache } from './soundfontInstrumentCache';
+
+class MockWritableFileStream {
+  private readonly handle: MockFileSystemFileHandle;
+  private chunks: Uint8Array[] = [];
+
+  constructor(handle: MockFileSystemFileHandle) {
+    this.handle = handle;
+  }
+
+  async write(content: Blob | ArrayBuffer | ArrayBufferView | string): Promise<void> {
+    let bytes: Uint8Array;
+    if (typeof content === 'string') {
+      bytes = new TextEncoder().encode(content);
+    } else if (typeof (content as Blob).arrayBuffer === 'function') {
+      bytes = new Uint8Array(await (content as Blob).arrayBuffer());
+    } else if (content instanceof ArrayBuffer) {
+      bytes = new Uint8Array(content);
+    } else {
+      const view = content as ArrayBufferView;
+      bytes = new Uint8Array(view.buffer, view.byteOffset, view.byteLength);
+    }
+    this.chunks.push(new Uint8Array(bytes));
+  }
+
+  async close(): Promise<void> {
+    const total = this.chunks.reduce((sum, chunk) => sum + chunk.byteLength, 0);
+    const merged = new Uint8Array(total);
+    let offset = 0;
+    for (const chunk of this.chunks) {
+      merged.set(chunk, offset);
+      offset += chunk.byteLength;
+    }
+    this.handle.setContent(merged);
+  }
+
+  async abort(): Promise<void> {
+    this.chunks = [];
+  }
+}
+
+class MockFileSystemFileHandle {
+  kind = 'file' as const;
+  private content = new Uint8Array();
+
+  constructor(public readonly name: string) {}
+
+  setContent(content: Uint8Array): void {
+    this.content = content;
+  }
+
+  async getFile(): Promise<File> {
+    return {
+      size: this.content.byteLength,
+      text: async () => new TextDecoder().decode(this.content),
+    } as unknown as File;
+  }
+
+  async createWritable(): Promise<MockWritableFileStream> {
+    return new MockWritableFileStream(this);
+  }
+}
+
+class MockFileSystemDirectoryHandle {
+  kind = 'directory' as const;
+  private children = new Map<string, MockFileSystemDirectoryHandle | MockFileSystemFileHandle>();
+
+  constructor(public readonly name: string) {}
+
+  async getDirectoryHandle(name: string, options?: { create?: boolean }): Promise<MockFileSystemDirectoryHandle> {
+    let child = this.children.get(name);
+    if (!child || child.kind !== 'directory') {
+      if (!options?.create) {
+        throw new DOMException(`Directory "${name}" not found`, 'NotFoundError');
+      }
+      child = new MockFileSystemDirectoryHandle(name);
+      this.children.set(name, child);
+    }
+    return child as MockFileSystemDirectoryHandle;
+  }
+
+  async getFileHandle(name: string, options?: { create?: boolean }): Promise<MockFileSystemFileHandle> {
+    let child = this.children.get(name);
+    if (!child || child.kind !== 'file') {
+      if (!options?.create) {
+        throw new DOMException(`File "${name}" not found`, 'NotFoundError');
+      }
+      child = new MockFileSystemFileHandle(name);
+      this.children.set(name, child);
+    }
+    return child as MockFileSystemFileHandle;
+  }
+
+  async removeEntry(name: string, options?: { recursive?: boolean }): Promise<void> {
+    const child = this.children.get(name);
+    if (!child) {
+      throw new DOMException(`Entry "${name}" not found`, 'NotFoundError');
+    }
+    if (child.kind === 'directory' && child.size() > 0 && !options?.recursive) {
+      throw new DOMException(`Directory "${name}" is not empty`, 'InvalidModificationError');
+    }
+    this.children.delete(name);
+  }
+
+  async *entries(): AsyncIterableIterator<[string, MockFileSystemDirectoryHandle | MockFileSystemFileHandle]> {
+    for (const entry of this.children.entries()) {
+      yield entry;
+    }
+  }
+
+  clear(): void {
+    this.children.clear();
+  }
+
+  size(): number {
+    return this.children.size;
+  }
+}
+
+const mockRoot = new MockFileSystemDirectoryHandle('root');
+
+vi.stubGlobal('navigator', {
+  ...navigator,
+  storage: {
+    getDirectory: vi.fn(async () => mockRoot),
+  },
+});
+
+describe('SoundfontInstrumentCache', () => {
+  const baseUrl = 'https://cdn.example.com/FluidR3_GM/';
+  const instrumentName = 'test_instrument';
+  const expectedKeys = ['C4', 'Db4'];
+  const blobsByKey = {
+    C4: new Blob([new Uint8Array([1, 2, 3])], { type: 'audio/mpeg' }),
+    Db4: new Blob([new Uint8Array([4, 5, 6])], { type: 'audio/mpeg' }),
+  };
+
+  beforeEach(async () => {
+    mockRoot.clear();
+    vi.restoreAllMocks();
+  });
+
+  it('stores and validates a finalized instrument cache', async () => {
+    await SoundfontInstrumentCache.storeInstrument(instrumentName, expectedKeys, blobsByKey, baseUrl);
+
+    const summary = await SoundfontInstrumentCache.getCacheSummary(baseUrl);
+    expect(summary.instrumentCount).toBe(1);
+    expect(summary.instruments).toEqual([instrumentName]);
+
+    const urls = await SoundfontInstrumentCache.getInstrumentObjectUrls(instrumentName, expectedKeys, baseUrl);
+    expect(Object.keys(urls)).toEqual(expectedKeys);
+    Object.values(urls).forEach(url => URL.revokeObjectURL(url));
+  });
+
+  it('rejects incomplete finalize attempts', async () => {
+    await expect(SoundfontInstrumentCache.storeInstrument(
+      instrumentName,
+      expectedKeys,
+      { C4: blobsByKey.C4 },
+      baseUrl,
+    )).rejects.toThrow(/incomplete key set/i);
+
+    expect(await SoundfontInstrumentCache.exists(instrumentName, expectedKeys, baseUrl)).toBe(false);
+  });
+
+  it('invalidates cached instruments when the base URL changes', async () => {
+    await SoundfontInstrumentCache.storeInstrument(instrumentName, expectedKeys, blobsByKey, baseUrl);
+    expect((await SoundfontInstrumentCache.getCacheSummary(baseUrl)).instrumentCount).toBe(1);
+
+    expect((await SoundfontInstrumentCache.getCacheSummary('https://other.example.com/FluidR3_GM/')).instrumentCount).toBe(0);
+    const summary = await SoundfontInstrumentCache.getCacheSummary('https://other.example.com/FluidR3_GM/');
+    expect(summary.instrumentCount).toBe(0);
+  });
+
+  it('treats broken cached instruments as invalid and removes them', async () => {
+    await SoundfontInstrumentCache.storeInstrument(instrumentName, expectedKeys, blobsByKey, baseUrl);
+
+    const root = await navigator.storage.getDirectory();
+    const soundfontDir = await root.getDirectoryHandle('soundfont');
+    const libraryDir = await soundfontDir.getDirectoryHandle('FluidR3_GM');
+    const instrumentDir = await libraryDir.getDirectoryHandle(instrumentName);
+    await instrumentDir.removeEntry('Db4.mp3');
+
+    expect(await SoundfontInstrumentCache.exists(instrumentName, expectedKeys, baseUrl)).toBe(false);
+    const summary = await SoundfontInstrumentCache.getCacheSummary(baseUrl);
+    expect(summary.instrumentCount).toBe(0);
+  });
+
+  it('deletes all cached instruments', async () => {
+    await SoundfontInstrumentCache.storeInstrument(instrumentName, expectedKeys, blobsByKey, baseUrl);
+    await SoundfontInstrumentCache.storeInstrument('other_instrument', expectedKeys, blobsByKey, baseUrl);
+
+    await SoundfontInstrumentCache.deleteAll();
+
+    const summary = await SoundfontInstrumentCache.getCacheSummary(baseUrl);
+    expect(summary.instrumentCount).toBe(0);
+  });
+});

src/util/soundfontInstrumentCache.ts

@@ -0,0 +1,226 @@
+interface SoundfontCacheRootMetadata {
+  baseUrl: string;
+  updatedAt: string;
+}
+
+interface SoundfontInstrumentMetadata {
+  complete: boolean;
+  keys: string[];
+  updatedAt: string;
+}
+
+export interface SoundfontCacheSummary {
+  instrumentCount: number;
+  instruments: string[];
+}
+
+const SOUND_FONT_ROOT_DIR = 'soundfont';
+const FLUIDR3_DIR = 'FluidR3_GM';
+const ROOT_METADATA_FILE = 'cache-metadata.json';
+const INSTRUMENT_METADATA_FILE = 'instrument-metadata.json';
+
+export class SoundfontInstrumentCache {
+  public static async exists(instrumentName: string, expectedKeys: string[], baseUrl: string): Promise<boolean> {
+    try {
+      const rootDir = await this.ensureLibraryDir(baseUrl);
+      const instrumentDir = await rootDir.getDirectoryHandle(instrumentName);
+      const metadata = await this.readJson<SoundfontInstrumentMetadata>(instrumentDir, INSTRUMENT_METADATA_FILE);
+      if (!metadata?.complete || !this.sameKeys(metadata.keys, expectedKeys)) {
+        await this.deleteInstrument(instrumentName);
+        return false;
+      }
+
+      for (const key of expectedKeys) {
+        const handle = await instrumentDir.getFileHandle(`${key}.mp3`);
+        const file = await handle.getFile();
+        if (file.size <= 0) {
+          await this.deleteInstrument(instrumentName);
+          return false;
+        }
+      }
+
+      return true;
+    } catch {
+      return false;
+    }
+  }
+
+  public static async getInstrumentObjectUrls(
+    instrumentName: string,
+    expectedKeys: string[],
+    baseUrl: string,
+  ): Promise<Record<string, string>> {
+    const rootDir = await this.ensureLibraryDir(baseUrl);
+    const instrumentDir = await rootDir.getDirectoryHandle(instrumentName);
+    const urls: Record<string, string> = {};
+
+    for (const key of expectedKeys) {
+      const fileHandle = await instrumentDir.getFileHandle(`${key}.mp3`);
+      const file = await fileHandle.getFile();
+      urls[key] = URL.createObjectURL(file);
+    }
+
+    return urls;
+  }
+
+  public static async storeInstrument(
+    instrumentName: string,
+    expectedKeys: string[],
+    blobsByKey: Record<string, Blob>,
+    baseUrl: string,
+  ): Promise<void> {
+    if (!this.sameKeys(Object.keys(blobsByKey), expectedKeys)) {
+      throw new Error(`Cannot finalize soundfont cache for ${instrumentName}: incomplete key set.`);
+    }
+
+    const rootDir = await this.ensureLibraryDir(baseUrl);
+    await this.removeIfExists(rootDir, instrumentName, true);
+    const instrumentDir = await rootDir.getDirectoryHandle(instrumentName, { create: true });
+
+    try {
+      for (const key of expectedKeys) {
+        const fileHandle = await instrumentDir.getFileHandle(`${key}.mp3`, { create: true });
+        const writable = await fileHandle.createWritable();
+        try {
+          await writable.write(blobsByKey[key]);
+          await writable.close();
+        } catch (error) {
+          await writable.abort();
+          throw error;
+        }
+      }
+
+      const metadata: SoundfontInstrumentMetadata = {
+        complete: true,
+        keys: [...expectedKeys],
+        updatedAt: new Date().toISOString(),
+      };
+      await this.writeJson(instrumentDir, INSTRUMENT_METADATA_FILE, metadata);
+    } catch (error) {
+      await this.removeIfExists(rootDir, instrumentName, true);
+      throw error;
+    }
+  }
+
+  public static async deleteInstrument(instrumentName: string): Promise<void> {
+    try {
+      const rootDir = await this.getLibraryDir(false);
+      if (!rootDir) return;
+      await this.removeIfExists(rootDir, instrumentName, true);
+    } catch {
+      // Ignore missing cache roots during cleanup.
+    }
+  }
+
+  public static async deleteAll(): Promise<void> {
+    try {
+      const rootDir = await this.getLibraryDir(false);
+      if (!rootDir) return;
+
+      for await (const [name] of rootDir.entries()) {
+        await this.removeIfExists(rootDir, name, true);
+      }
+    } catch {
+      // Ignore cleanup failures for missing cache roots.
+    }
+  }
+
+  public static async getCacheSummary(baseUrl: string): Promise<SoundfontCacheSummary> {
+    const rootDir = await this.ensureLibraryDir(baseUrl);
+    const instruments: string[] = [];
+
+    for await (const [name, entry] of rootDir.entries()) {
+      if (entry.kind !== 'directory') continue;
+
+      try {
+        const metadata = await this.readJson<SoundfontInstrumentMetadata>(entry, INSTRUMENT_METADATA_FILE);
+        if (metadata?.complete) {
+          instruments.push(name);
+        }
+      } catch {
+        // Ignore broken entries in summary output.
+      }
+    }
+
+    instruments.sort();
+    return {
+      instrumentCount: instruments.length,
+      instruments,
+    };
+  }
+
+  private static async ensureLibraryDir(baseUrl: string): Promise<FileSystemDirectoryHandle> {
+    const root = await navigator.storage.getDirectory();
+    const soundfontDir = await root.getDirectoryHandle(SOUND_FONT_ROOT_DIR, { create: true });
+    const libraryDir = await soundfontDir.getDirectoryHandle(FLUIDR3_DIR, { create: true });
+    const metadata = await this.readRootMetadata(libraryDir);
+
+    if (!metadata || metadata.baseUrl !== baseUrl) {
+      for await (const [name] of libraryDir.entries()) {
+        await this.removeIfExists(libraryDir, name, true);
+      }
+
+      const nextMetadata: SoundfontCacheRootMetadata = {
+        baseUrl,
+        updatedAt: new Date().toISOString(),
+      };
+      await this.writeJson(libraryDir, ROOT_METADATA_FILE, nextMetadata);
+    }
+
+    return libraryDir;
+  }
+
+  private static async getLibraryDir(create: boolean): Promise<FileSystemDirectoryHandle | null> {
+    try {
+      const root = await navigator.storage.getDirectory();
+      const soundfontDir = await root.getDirectoryHandle(SOUND_FONT_ROOT_DIR, { create });
+      return await soundfontDir.getDirectoryHandle(FLUIDR3_DIR, { create });
+    } catch {
+      return null;
+    }
+  }
+
+  private static async readRootMetadata(dir: FileSystemDirectoryHandle): Promise<SoundfontCacheRootMetadata | null> {
+    try {
+      return await this.readJson<SoundfontCacheRootMetadata>(dir, ROOT_METADATA_FILE);
+    } catch {
+      return null;
+    }
+  }
+
+  private static async readJson<T>(dir: FileSystemDirectoryHandle, filename: string): Promise<T> {
+    const handle = await dir.getFileHandle(filename);
+    const file = await handle.getFile();
+    return JSON.parse(await file.text()) as T;
+  }
+
+  private static async writeJson(dir: FileSystemDirectoryHandle, filename: string, value: unknown): Promise<void> {
+    const handle = await dir.getFileHandle(filename, { create: true });
+    const writable = await handle.createWritable();
+    try {
+      await writable.write(JSON.stringify(value, null, 2));
+      await writable.close();
+    } catch (error) {
+      await writable.abort();
+      throw error;
+    }
+  }
+
+  private static sameKeys(actual: string[], expected: string[]): boolean {
+    if (actual.length !== expected.length) return false;
+    const expectedSet = new Set(expected);
+    return actual.every(key => expectedSet.has(key));
+  }
+
+  private static async removeIfExists(
+    dir: FileSystemDirectoryHandle,
+    name: string,
+    recursive: boolean = false,
+  ): Promise<void> {
+    try {
+      await dir.removeEntry(name, recursive ? ({ recursive: true } as FileSystemRemoveOptions) : undefined);
+    } catch {
+      // Ignore missing entry cleanup.
+    }
+  }
+}