feat: add LogViewer composite for timestamped, severity-colored log display

Scrollable log viewer with auto-scroll behavior, level badges (info/warn/
error/debug) with semantic colors, monospace font, and role="log" for
accessibility. Includes 7 tests and barrel exports.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/design-system/composites/LogViewer/LogViewer.module.css

@@ -0,0 +1,75 @@
+.container {
+  overflow-y: auto;
+  background: var(--bg-inset);
+  border-radius: var(--radius-md);
+  padding: 8px 0;
+  font-family: var(--font-mono);
+}
+
+.line {
+  display: flex;
+  align-items: flex-start;
+  gap: 8px;
+  padding: 3px 12px;
+  line-height: 1.5;
+}
+
+.line:hover {
+  background: var(--bg-hover);
+}
+
+.timestamp {
+  flex-shrink: 0;
+  font-size: 11px;
+  color: var(--text-muted);
+  min-width: 56px;
+}
+
+.levelBadge {
+  flex-shrink: 0;
+  font-size: 9px;
+  font-weight: 600;
+  font-family: var(--font-mono);
+  text-transform: uppercase;
+  letter-spacing: 0.3px;
+  padding: 1px 6px;
+  border-radius: 9999px;
+  line-height: 1.5;
+  white-space: nowrap;
+}
+
+.levelInfo {
+  color: var(--running);
+  background: color-mix(in srgb, var(--running) 12%, transparent);
+}
+
+.levelWarn {
+  color: var(--warning);
+  background: color-mix(in srgb, var(--warning) 12%, transparent);
+}
+
+.levelError {
+  color: var(--error);
+  background: color-mix(in srgb, var(--error) 12%, transparent);
+}
+
+.levelDebug {
+  color: var(--text-muted);
+  background: color-mix(in srgb, var(--text-muted) 10%, transparent);
+}
+
+.message {
+  font-size: 12px;
+  font-family: var(--font-mono);
+  color: var(--text-primary);
+  word-break: break-word;
+  line-height: 1.5;
+}
+
+.empty {
+  padding: 24px;
+  text-align: center;
+  color: var(--text-faint);
+  font-size: 12px;
+  font-family: var(--font-body);
+}

src/design-system/composites/LogViewer/LogViewer.test.tsx

@@ -0,0 +1,56 @@
+import { describe, it, expect } from 'vitest'
+import { render, screen } from '@testing-library/react'
+import { LogViewer, type LogEntry } from './LogViewer'
+
+const entries: LogEntry[] = [
+  { timestamp: '2024-01-15T10:30:00Z', level: 'info', message: 'Server started' },
+  { timestamp: '2024-01-15T10:30:05Z', level: 'warn', message: 'High memory usage' },
+  { timestamp: '2024-01-15T10:30:10Z', level: 'error', message: 'Connection failed' },
+  { timestamp: '2024-01-15T10:30:15Z', level: 'debug', message: 'Query executed in 3ms' },
+]
+
+describe('LogViewer', () => {
+  it('renders entries with timestamps and messages', () => {
+    render(<LogViewer entries={entries} />)
+    expect(screen.getByText('Server started')).toBeInTheDocument()
+    expect(screen.getByText('High memory usage')).toBeInTheDocument()
+    expect(screen.getByText('Connection failed')).toBeInTheDocument()
+    expect(screen.getByText('Query executed in 3ms')).toBeInTheDocument()
+  })
+
+  it('renders level badges with correct text (INFO, WARN, ERROR, DEBUG)', () => {
+    render(<LogViewer entries={entries} />)
+    expect(screen.getByText('INFO')).toBeInTheDocument()
+    expect(screen.getByText('WARN')).toBeInTheDocument()
+    expect(screen.getByText('ERROR')).toBeInTheDocument()
+    expect(screen.getByText('DEBUG')).toBeInTheDocument()
+  })
+
+  it('renders with custom maxHeight (number)', () => {
+    const { container } = render(<LogViewer entries={entries} maxHeight={300} />)
+    const el = container.firstElementChild as HTMLElement
+    expect(el.style.maxHeight).toBe('300px')
+  })
+
+  it('renders with string maxHeight', () => {
+    const { container } = render(<LogViewer entries={entries} maxHeight="50vh" />)
+    const el = container.firstElementChild as HTMLElement
+    expect(el.style.maxHeight).toBe('50vh')
+  })
+
+  it('handles empty entries', () => {
+    render(<LogViewer entries={[]} />)
+    expect(screen.getByText('No log entries.')).toBeInTheDocument()
+  })
+
+  it('accepts className prop', () => {
+    const { container } = render(<LogViewer entries={entries} className="custom-class" />)
+    const el = container.firstElementChild as HTMLElement
+    expect(el.classList.contains('custom-class')).toBe(true)
+  })
+
+  it('has role="log" for accessibility', () => {
+    render(<LogViewer entries={entries} />)
+    expect(screen.getByRole('log')).toBeInTheDocument()
+  })
+})

src/design-system/composites/LogViewer/LogViewer.tsx

@@ -0,0 +1,77 @@
+import { useRef, useEffect, useCallback } from 'react'
+import styles from './LogViewer.module.css'
+
+export interface LogEntry {
+  timestamp: string
+  level: 'info' | 'warn' | 'error' | 'debug'
+  message: string
+}
+
+export interface LogViewerProps {
+  entries: LogEntry[]
+  maxHeight?: number | string
+  className?: string
+}
+
+const LEVEL_CLASS: Record<LogEntry['level'], string> = {
+  info: styles.levelInfo,
+  warn: styles.levelWarn,
+  error: styles.levelError,
+  debug: styles.levelDebug,
+}
+
+function formatTime(iso: string): string {
+  try {
+    return new Date(iso).toLocaleTimeString('en-GB', {
+      hour: '2-digit',
+      minute: '2-digit',
+      second: '2-digit',
+      hour12: false,
+    })
+  } catch {
+    return iso
+  }
+}
+
+export function LogViewer({ entries, maxHeight = 400, className }: LogViewerProps) {
+  const scrollRef = useRef<HTMLDivElement>(null)
+  const isAtBottomRef = useRef(true)
+
+  const handleScroll = useCallback(() => {
+    const el = scrollRef.current
+    if (!el) return
+    isAtBottomRef.current = el.scrollHeight - el.scrollTop - el.clientHeight < 20
+  }, [])
+
+  useEffect(() => {
+    const el = scrollRef.current
+    if (el && isAtBottomRef.current) {
+      el.scrollTop = el.scrollHeight
+    }
+  }, [entries])
+
+  const heightStyle = typeof maxHeight === 'number' ? `${maxHeight}px` : maxHeight
+
+  return (
+    <div
+      ref={scrollRef}
+      className={[styles.container, className].filter(Boolean).join(' ')}
+      style={{ maxHeight: heightStyle }}
+      onScroll={handleScroll}
+      role="log"
+    >
+      {entries.map((entry, i) => (
+        <div key={i} className={styles.line}>
+          <span className={styles.timestamp}>{formatTime(entry.timestamp)}</span>
+          <span className={[styles.levelBadge, LEVEL_CLASS[entry.level]].join(' ')}>
+            {entry.level.toUpperCase()}
+          </span>
+          <span className={styles.message}>{entry.message}</span>
+        </div>
+      ))}
+      {entries.length === 0 && (
+        <div className={styles.empty}>No log entries.</div>
+      )}
+    </div>
+  )
+}

src/design-system/composites/index.ts

@@ -20,6 +20,8 @@ export type { KpiItem, KpiStripProps } from './KpiStrip/KpiStrip'
 export type { FeedEvent } from './EventFeed/EventFeed'
 export { FilterBar } from './FilterBar/FilterBar'
 export { LineChart } from './LineChart/LineChart'
+export { LogViewer } from './LogViewer/LogViewer'
+export type { LogEntry, LogViewerProps } from './LogViewer/LogViewer'
 export { LoginDialog } from './LoginForm/LoginDialog'
 export type { LoginDialogProps } from './LoginForm/LoginDialog'
 export { LoginForm } from './LoginForm/LoginForm'