fix: Fix undici browser compatibility with dynamic imports

[scottlovegrove]

Summary

Resolves browser compatibility issues with undici by replacing static imports with dynamic imports and environment detection.

• Problem: Static undici import caused Cannot read properties of undefined (reading 'node') errors in browser environments
• Solution: Dynamic import that only loads undici in Node.js environments using process.versions?.node detection
• Impact: Enables browser usage while maintaining Node.js performance benefits

Have tested this with the Todoist Outlook add-in as this is where it was originally found.

Changes

• Remove static import { Agent } from 'undici'
• Add getHttpAgent() function with environment detection
• Implement dynamic await import('undici') for Node.js only
• Cache agent instance to prevent multiple imports
• Update fetchWithRetry to use await getHttpAgent()

Browser Compatibility

✅ Before: TypeError: Cannot read properties of undefined (reading 'node')
✅ After: No errors, undici never loaded in browser environments

Testing

• ✅ All 262 existing tests pass in Node.js
• ✅ TypeScript compilation succeeds without errors
• ✅ Vite build completes successfully in browser environment
• ✅ No breaking changes for existing Node.js usage
• ✅ Custom fetch adapters (like Obsidian) continue working unchanged

Backward Compatibility

Zero breaking changes - all existing code continues to work:

• Node.js users still get undici Agent benefits (connection pooling, keepAlive management)
• Custom fetch users have no overhead (agent never created)
• Browser users can now use the SDK without errors

🤖 Generated with Claude Code