Compensation Handler

# Compensation Handler

Undo completed steps when a multi-step operation fails.

## Category
Tool Execution

## Context
Multi-step operations across systems that can't use traditional transactions.

## Problem
Cross-system operations can't be rolled back atomically; completed steps need explicit undo.

## Solution
Implement compensation logic:
- **Track completed steps**: Know what succeeded
- **Define compensating actions**: Undo for each step
- **Execute in reverse**: Compensate in reverse order
- **Log everything**: Audit trail for debugging

## Example (Python)
```python
@tool
def provision_customer(data: CustomerData) -> ProvisionResult:
    """Provision a new customer across systems.
    
    If any step fails, previous steps are compensated.
    """
    completed = []
    try:
        account = create_account(data)
        completed.append(("account", account.id))
        
        billing = setup_billing(account.id)
        completed.append(("billing", billing.id))
        
        access = grant_access(account.id)
        completed.append(("access", access.id))
        
        return ProvisionResult(success=True, account=account)
    except Exception as e:
        compensate(completed)  # Undo in reverse order
        raise
```

## Considerations
- Some actions may not be fully reversible
- Log compensation actions for audit
- Consider async compensation for slow undos

## Related Patterns
- transactional-boundary
- tool-chain
- partial-success

---
Source: https://arcade.dev/patterns/compensation-handler