## Recent Updates (August 22, 2025)

### Duplicate Period Prevention

We've implemented a safeguard mechanism to prevent duplicate period uploads in the payroll system with the following features:

1. **Unique Period Constraint**:
   - Added database-level constraint to prevent duplicate period date ranges
   - Each pay period (defined by start and end date) can only be uploaded once
   - System will reject attempts to upload the same period multiple times

2. **User-Friendly Error Messages**:
   - Clear error messages when attempting to upload a duplicate period
   - HTTP 409 Conflict status code for proper error handling in the frontend
   - Detailed information about why the upload was rejected

3. **Technical Implementation**:
   - Added unique constraint on period_start and period_end columns in the timesheet_periods table
   - Enhanced validation in the Timesheet model to check for existing periods
   - Updated controllers to handle duplicate period errors gracefully

This enhancement prevents accidental duplication of timesheet data, which could lead to payroll calculation errors or double payments. It ensures data integrity and improves the overall reliability of the system.