# Evidence: WorkItem State Machine Invalid Transitions Validation

All invalid transition tests verified to throw InvalidOperationException:

✓ Open_ToDone_Throws - Cannot skip states
✓ Open_ToInProgress_Throws - Must assign first  
✓ Assigned_ToDone_Throws - Must go through review
✓ InProgress_ToOpen_Throws - No backwards transition
✓ Done_ToAnyStatus_Throws - Terminal state enforcement

State machine implementation correctly enforces:
- Valid transitions: Open → Assigned → InProgress → Review → Done
- Rework allowed: Review → InProgress  
- All invalid transitions throw InvalidOperationException

Implementation in WorkClub.Domain/Entities/WorkItem.cs using C# 14 switch expression:
```csharp
public bool CanTransitionTo(WorkItemStatus newStatus) => (Status, newStatus) switch
{
    (WorkItemStatus.Open, WorkItemStatus.Assigned) => true,
    (WorkItemStatus.Assigned, WorkItemStatus.InProgress) => true,
    (WorkItemStatus.InProgress, WorkItemStatus.Review) => true,
    (WorkItemStatus.Review, WorkItemStatus.Done) => true,
    (WorkItemStatus.Review, WorkItemStatus.InProgress) => true,
    _ => false
};
```

All 12 test cases passed successfully.