feat: add Vitest unit tests for utility functions

- Set up Vitest with 27 tests across 3 test suites
- relativeTime: edge cases, time buckets, future timestamps
- sessionDisplayName: labels, kinds, channels, UUID truncation
- messagesToMarkdown: roles, blocks, tool calls, system events
- Add test and test:watch npm scripts
- Add test step to CI workflow

src/lib/__tests__/exportChat.test.ts

@@ -0,0 +1,84 @@
+import { describe, it, expect, vi } from 'vitest';
+import { messagesToMarkdown } from '../exportChat';
+import type { ChatMessage } from '../../types';
+
+function makeMessage(overrides: Partial<ChatMessage> = {}): ChatMessage {
+  return {
+    id: '1',
+    role: 'user',
+    content: 'Hello world',
+    timestamp: new Date('2026-01-15T10:30:00Z').getTime(),
+    blocks: [],
+    isSystemEvent: false,
+    ...overrides,
+  } as ChatMessage;
+}
+
+describe('messagesToMarkdown', () => {
+  it('includes session label as heading', () => {
+    const md = messagesToMarkdown([], 'Test Session');
+    expect(md).toContain('# Test Session');
+  });
+
+  it('includes export timestamp', () => {
+    const md = messagesToMarkdown([]);
+    expect(md).toContain('Exported from PinchChat on');
+  });
+
+  it('labels user messages with 👤 User', () => {
+    const md = messagesToMarkdown([makeMessage({ role: 'user' })]);
+    expect(md).toContain('👤 User');
+  });
+
+  it('labels assistant messages with 🤖 Assistant', () => {
+    const md = messagesToMarkdown([makeMessage({ role: 'assistant' })]);
+    expect(md).toContain('🤖 Assistant');
+  });
+
+  it('labels system events with ⚙️ System Event', () => {
+    const md = messagesToMarkdown([makeMessage({ role: 'user', isSystemEvent: true })]);
+    expect(md).toContain('⚙️ System Event');
+  });
+
+  it('renders text blocks', () => {
+    const md = messagesToMarkdown([makeMessage({
+      content: '',
+      blocks: [{ type: 'text', text: 'Some content here' }],
+    })]);
+    expect(md).toContain('Some content here');
+  });
+
+  it('renders tool_use blocks with name and input', () => {
+    const md = messagesToMarkdown([makeMessage({
+      role: 'assistant',
+      content: '',
+      blocks: [{ type: 'tool_use', name: 'exec', input: { command: 'ls' } }],
+    })]);
+    expect(md).toContain('`exec`');
+    expect(md).toContain('"command": "ls"');
+  });
+
+  it('falls back to content when blocks are empty', () => {
+    const md = messagesToMarkdown([makeMessage({ content: 'Fallback text', blocks: [] })]);
+    expect(md).toContain('Fallback text');
+  });
+
+  it('renders image blocks as placeholder', () => {
+    const md = messagesToMarkdown([makeMessage({
+      content: '',
+      blocks: [{ type: 'image', mediaType: 'image/png' }],
+    })]);
+    expect(md).toContain('*[Image]*');
+  });
+
+  it('wraps thinking blocks in details tags', () => {
+    vi.stubGlobal('Date', globalThis.Date);
+    const md = messagesToMarkdown([makeMessage({
+      role: 'assistant',
+      content: '',
+      blocks: [{ type: 'thinking', text: 'Let me think...' }],
+    })]);
+    expect(md).toContain('<details><summary>💭 Thinking</summary>');
+    expect(md).toContain('Let me think...');
+  });
+});

src/lib/__tests__/relativeTime.test.ts

@@ -0,0 +1,57 @@
+import { describe, it, expect, vi, afterEach } from 'vitest';
+import { relativeTime } from '../relativeTime';
+
+describe('relativeTime', () => {
+  afterEach(() => {
+    vi.restoreAllMocks();
+  });
+
+  it('returns null for undefined', () => {
+    expect(relativeTime(undefined)).toBeNull();
+  });
+
+  it('returns null for 0', () => {
+    expect(relativeTime(0)).toBeNull();
+  });
+
+  it('returns "<1m" for timestamps less than 60s ago', () => {
+    const now = Date.now();
+    vi.spyOn(Date, 'now').mockReturnValue(now);
+    expect(relativeTime(now - 30_000)).toBe('<1m');
+    expect(relativeTime(now)).toBe('<1m');
+  });
+
+  it('returns minutes for 1-59 minutes ago', () => {
+    const now = Date.now();
+    vi.spyOn(Date, 'now').mockReturnValue(now);
+    expect(relativeTime(now - 60_000)).toBe('1m');
+    expect(relativeTime(now - 45 * 60_000)).toBe('45m');
+  });
+
+  it('returns hours for 1-23 hours ago', () => {
+    const now = Date.now();
+    vi.spyOn(Date, 'now').mockReturnValue(now);
+    expect(relativeTime(now - 3_600_000)).toBe('1h');
+    expect(relativeTime(now - 23 * 3_600_000)).toBe('23h');
+  });
+
+  it('returns days for 1-29 days ago', () => {
+    const now = Date.now();
+    vi.spyOn(Date, 'now').mockReturnValue(now);
+    expect(relativeTime(now - 86_400_000)).toBe('1d');
+    expect(relativeTime(now - 7 * 86_400_000)).toBe('7d');
+  });
+
+  it('returns months for 30+ days ago', () => {
+    const now = Date.now();
+    vi.spyOn(Date, 'now').mockReturnValue(now);
+    expect(relativeTime(now - 30 * 86_400_000)).toBe('1mo');
+    expect(relativeTime(now - 90 * 86_400_000)).toBe('3mo');
+  });
+
+  it('clamps negative diff to 0 (future timestamps)', () => {
+    const now = Date.now();
+    vi.spyOn(Date, 'now').mockReturnValue(now);
+    expect(relativeTime(now + 60_000)).toBe('<1m');
+  });
+});

src/lib/__tests__/sessionName.test.ts

@@ -0,0 +1,61 @@
+import { describe, it, expect } from 'vitest';
+import { sessionDisplayName } from '../sessionName';
+import type { Session } from '../../types';
+
+function makeSession(overrides: Partial<Session> = {}): Session {
+  return {
+    key: 'agent:main:test',
+    kind: 'main',
+    channel: '',
+    lastActivity: Date.now(),
+    ...overrides,
+  } as Session;
+}
+
+describe('sessionDisplayName', () => {
+  it('returns label when set', () => {
+    expect(sessionDisplayName(makeSession({ label: 'My Task' }))).toBe('My Task');
+  });
+
+  it('returns "Main" for main sessions without channel', () => {
+    expect(sessionDisplayName(makeSession({ kind: 'main', channel: '' }))).toBe('Main');
+  });
+
+  it('returns "Main · Discord" for main sessions with channel', () => {
+    expect(sessionDisplayName(makeSession({ kind: 'main', channel: 'discord' }))).toBe('Main · Discord');
+  });
+
+  it('returns "Cron" for cron sessions without channel', () => {
+    expect(sessionDisplayName(makeSession({ kind: 'cron', channel: '' }))).toBe('Cron');
+  });
+
+  it('returns "Cron · Telegram" for cron sessions with channel', () => {
+    expect(sessionDisplayName(makeSession({ kind: 'cron', channel: 'telegram' }))).toBe('Cron · Telegram');
+  });
+
+  it('returns "Task · Discord" for isolated sessions', () => {
+    expect(sessionDisplayName(makeSession({ kind: 'isolated', channel: 'discord' }))).toBe('Task · Discord');
+  });
+
+  it('returns capitalized channel as fallback', () => {
+    expect(sessionDisplayName(makeSession({ kind: undefined as unknown as string, channel: 'slack' } as Partial<Session>))).toBe('Slack');
+  });
+
+  it('truncates UUID session keys', () => {
+    const name = sessionDisplayName(makeSession({
+      kind: undefined as unknown as string,
+      channel: '',
+      key: 'agent:main:a1b2c3d4-e5f6-7890-abcd-ef1234567890',
+    } as Partial<Session>));
+    expect(name).toBe('a1b2c3d4…');
+  });
+
+  it('strips agent prefix from non-UUID keys', () => {
+    const name = sessionDisplayName(makeSession({
+      kind: undefined as unknown as string,
+      channel: '',
+      key: 'agent:bot:mycustomkey',
+    } as Partial<Session>));
+    expect(name).toBe('mycustomkey');
+  });
+});