feat: automatic unselection of discounted transportation

docs/PROJECT_OVERVIEW.md

@@ -231,6 +231,13 @@ Critical for correct pricing and auto-reassignment:
 - **Unified pickup field**: Single field for both directions (BPN API limitation)
 - **Conditional visibility**: Pickup vs parking fields mutually exclusive
 - **Direction mapping**: `DirectionMapper` translates API ↔ internal codes
+- **Discount replacement logic**: Automatic correction of incompatible transportation combinations
+  - When inbound bus selected with discounted PKW outbound: system automatically replaces with regular PKW
+  - When inbound changes from bus to PKW: system automatically restores discounted PKW if available
+  - Form options update dynamically to show only valid PKW variant
+  - User notified via toast messages about automatic changes
+  - Implemented via `ParticipantTransportationDiscountReplacementFieldHandler`
+  - Prevents invalid pricing where user gets both PKW discount and bus pricing
 
 ## Important Field Dependencies
 
@@ -430,8 +437,9 @@ Edit mode session requires proper cleanup to prevent dirty state persistence:
 - `src/Form/Service/EditFieldStateProvider.php` - Edit mode mutability constraints
 
 ### Field Handlers
-- `src/Form/Service/Participant*FieldHandler.php` (15+ handlers)
-- Transportation, pickup, parking, ski pass, rentals, insurance, bulk insurance, etc.
+- `src/Form/Service/Participant*FieldHandler.php` (16+ handlers)
+- Transportation (outbound, inbound, discount replacement), pickup, parking, ski pass, rentals, insurance, bulk insurance, etc.
+- `ParticipantTransportationDiscountReplacementFieldHandler` - Automatic discount replacement for invalid transportation combinations
 
 ## Testing