diff --git a/src/lib/__tests__/credentials.test.ts b/src/lib/__tests__/credentials.test.ts
new file mode 100644
index 0000000..c61cf28
--- /dev/null
+++ b/src/lib/__tests__/credentials.test.ts
@@ -0,0 +1,61 @@
+import { describe, it, expect, beforeEach, vi } from 'vitest';
+import { getStoredCredentials, storeCredentials, clearCredentials } from '../credentials';
+
+// Mock localStorage
+const store: Record<string, string> = {};
+const localStorageMock = {
+  getItem: vi.fn((key: string) => store[key] ?? null),
+  setItem: vi.fn((key: string, value: string) => { store[key] = value; }),
+  removeItem: vi.fn((key: string) => { delete store[key]; }),
+};
+
+Object.defineProperty(globalThis, 'localStorage', { value: localStorageMock });
+
+beforeEach(() => {
+  for (const key of Object.keys(store)) delete store[key];
+  vi.clearAllMocks();
+});
+
+describe('getStoredCredentials', () => {
+  it('returns null when nothing stored', () => {
+    expect(getStoredCredentials()).toBeNull();
+  });
+
+  it('returns credentials when valid JSON stored', () => {
+    store['pinchchat_credentials'] = JSON.stringify({ url: 'wss://gw.test', token: 'abc' });
+    expect(getStoredCredentials()).toEqual({ url: 'wss://gw.test', token: 'abc' });
+  });
+
+  it('returns null for malformed JSON', () => {
+    store['pinchchat_credentials'] = 'not-json';
+    expect(getStoredCredentials()).toBeNull();
+  });
+
+  it('returns null if url is missing', () => {
+    store['pinchchat_credentials'] = JSON.stringify({ token: 'abc' });
+    expect(getStoredCredentials()).toBeNull();
+  });
+
+  it('returns null if token is missing', () => {
+    store['pinchchat_credentials'] = JSON.stringify({ url: 'wss://gw' });
+    expect(getStoredCredentials()).toBeNull();
+  });
+});
+
+describe('storeCredentials', () => {
+  it('stores credentials as JSON', () => {
+    storeCredentials('wss://gw', 'tok');
+    expect(localStorageMock.setItem).toHaveBeenCalledWith(
+      'pinchchat_credentials',
+      JSON.stringify({ url: 'wss://gw', token: 'tok' }),
+    );
+  });
+});
+
+describe('clearCredentials', () => {
+  it('removes the key from localStorage', () => {
+    store['pinchchat_credentials'] = 'something';
+    clearCredentials();
+    expect(localStorageMock.removeItem).toHaveBeenCalledWith('pinchchat_credentials');
+  });
+});
diff --git a/src/lib/__tests__/image.test.ts b/src/lib/__tests__/image.test.ts
new file mode 100644
index 0000000..12c2234
--- /dev/null
+++ b/src/lib/__tests__/image.test.ts
@@ -0,0 +1,32 @@
+import { describe, it, expect } from 'vitest';
+import { buildImageSrc } from '../image';
+
+describe('buildImageSrc', () => {
+  it('returns URL when url is provided', () => {
+    expect(buildImageSrc('image/png', undefined, 'https://example.com/img.png'))
+      .toBe('https://example.com/img.png');
+  });
+
+  it('prefers url over base64 data', () => {
+    expect(buildImageSrc('image/png', 'abc123', 'https://example.com/img.png'))
+      .toBe('https://example.com/img.png');
+  });
+
+  it('builds data URL from base64 data', () => {
+    expect(buildImageSrc('image/png', 'abc123'))
+      .toBe('data:image/png;base64,abc123');
+  });
+
+  it('builds data URL for jpeg', () => {
+    expect(buildImageSrc('image/jpeg', 'xyz'))
+      .toBe('data:image/jpeg;base64,xyz');
+  });
+
+  it('returns empty string when neither url nor data provided', () => {
+    expect(buildImageSrc('image/png')).toBe('');
+  });
+
+  it('returns empty string with undefined data and no url', () => {
+    expect(buildImageSrc('image/webp', undefined, undefined)).toBe('');
+  });
+});
diff --git a/src/lib/__tests__/utils.test.ts b/src/lib/__tests__/utils.test.ts
new file mode 100644
index 0000000..e89ddea
--- /dev/null
+++ b/src/lib/__tests__/utils.test.ts
@@ -0,0 +1,52 @@
+import { describe, it, expect } from 'vitest';
+import { cn, genId, genIdempotencyKey } from '../utils';
+
+describe('cn', () => {
+  it('merges class names', () => {
+    expect(cn('foo', 'bar')).toBe('foo bar');
+  });
+
+  it('handles conditional classes', () => {
+    const showHidden = false;
+    expect(cn('base', showHidden && 'hidden', 'extra')).toBe('base extra');
+  });
+
+  it('resolves tailwind conflicts (twMerge)', () => {
+    // twMerge deduplicates conflicting tailwind utilities
+    expect(cn('p-4', 'p-2')).toBe('p-2');
+  });
+
+  it('handles empty input', () => {
+    expect(cn()).toBe('');
+  });
+
+  it('handles undefined and null values', () => {
+    expect(cn('a', undefined, null, 'b')).toBe('a b');
+  });
+});
+
+describe('genId', () => {
+  it('generates unique ids with default prefix', () => {
+    const a = genId();
+    const b = genId();
+    expect(a).toMatch(/^req-\d+-\d+$/);
+    expect(a).not.toBe(b);
+  });
+
+  it('uses custom prefix', () => {
+    expect(genId('msg')).toMatch(/^msg-\d+-\d+$/);
+  });
+});
+
+describe('genIdempotencyKey', () => {
+  it('returns a non-empty string', () => {
+    const key = genIdempotencyKey();
+    expect(key.length).toBeGreaterThan(0);
+  });
+
+  it('generates unique keys', () => {
+    const a = genIdempotencyKey();
+    const b = genIdempotencyKey();
+    expect(a).not.toBe(b);
+  });
+});