wip: update docs

docs/FIELD_STATE_SYSTEM.md

@@ -180,6 +180,41 @@ The system supports real-time field state updates:
 3. HTMX can update field states without full page refresh
 4. Dependency tracking ensures only affected fields are updated
 
+### Service Field HTMX Integration Improvements
+
+**Critical Fix for Expanded Choice Fields**: Service fields (board, skipass, courses, etc.) use expanded choice types (checkboxes/radios) which required special HTMX trigger handling:
+
+**Issue Resolved**: HTMX attributes were originally placed on container elements (`row_attr`) which don't capture individual input changes for expanded choice fields.
+
+**Solution Implemented**: HTMX triggers must be placed directly on each individual checkbox/radio input via the `attr` configuration:
+
+```php
+// Correct implementation for service fields
+'attr' => [
+    'hx-post' => $this->urlGenerator->generate('booking_create_step_2_refresh'),
+    'hx-target' => '#booking-summary', 
+    'hx-trigger' => 'change',
+],
+
+// Incorrect approach (doesn't work for expanded choices)
+// 'row_attr' => ['hx-post' => '...']
+```
+
+**Benefits of the Fix**:
+- Real-time updates now work reliably for all service field selections
+- Service pricing calculations update immediately when selections change
+- Booking summary reflects service changes without manual form submission
+- Consistent HTMX behavior across all form field types
+
+**Affected Field Types**:
+- Board/meal selection fields
+- Ski pass selection fields  
+- Course selection fields
+- Additional services selection fields
+- Rental equipment selection fields
+
+This improvement ensures that the conditional field state system works seamlessly with HTMX for all field types, providing users with immediate feedback on their selections.
+
 ## Extending the System
 
 ### Custom Conditions