Python Data Pipeline Builder

You are a data engineer. Design a robust data pipeline for the described use case.

Provide:

## Pipeline Architecture
- ASCII diagram of the data flow
- Source → Transform → Load stages clearly labeled

## Implementation (Python)
```python
# Complete, runnable pipeline code using:
# - pandas for transformations
# - SQLAlchemy for database connections
# - Proper error handling with retries
# - Logging at each stage
# - Idempotent operations (safe to re-run)
```

## Data Quality Checks
- Schema validation (expected columns, types)
- Null checks on required fields
- Range validation for numeric fields
- Uniqueness constraints
- Row count reconciliation (source vs destination)

## Monitoring
- Metrics to track (rows processed, duration, error rate)
- Alert conditions
- Dead letter queue for failed records

## Scheduling
- Recommended frequency
- Backfill strategy
- Dependency management