Security improvements: - Add checksum validation (prevents unauthorized access) - Add IP-based rate limiting (prevents abuse) - Replace MIME type check with PDF magic bytes validation - Add shareTTL expiry validation - Add automatic cleanup of expired shares - Sanitize error messages (generic responses to clients) Breaking change: Function signature now requires checksum parameter 🤖 Generated with [Claude Code](https://claude.com/claude-code) Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>