fix: pass BusPro room assignments through on edit

tests/Service/BookingEditDraftMergerRoomAssignmentTest.php

@@ -13,13 +13,12 @@ use App\Service\ServiceAvailabilityCalculator;
 use PHPUnit\Framework\TestCase;
 
 /**
- * Tests that draft restoration never unassigns a room.
+ * Tests that draft restoration never changes a room assignment.
  *
- * Edit mode renders the room as static text and never submits assignedRoomId, so a null in
- * the draft payload is always an artefact of a snapshot taken before BusPro reported the
- * assignment - typically for seats added to a group booking shortly before the draft was
- * saved. Replaying such a null would strip the room from the UI and from the outbound
- * zuordnung, so the room id uses the same merge strategy as single-select services.
+ * Edit mode renders the room as static text and never submits assignedRoomId, so the draft
+ * only holds what BusPro reported when it was saved: a null for seats added to a group booking
+ * shortly before, or a room the office has since reassigned. The room always comes from the
+ * booking as loaded; only the free-text remarks are restored.
  */
 class BookingEditDraftMergerRoomAssignmentTest extends TestCase
 {
@@ -43,7 +42,7 @@ class BookingEditDraftMergerRoomAssignmentTest extends TestCase
         $this->assertSame(74, $participant->assignedRoomId);
     }
 
-    public function testDraftAppliesRoomThatResolvesAgainstTravel(): void
+    public function testDraftDoesNotMoveParticipantToAnotherRoom(): void
     {
         $participant = new ParticipantDto();
         $participant->mutable = true;
@@ -56,7 +55,7 @@ class BookingEditDraftMergerRoomAssignmentTest extends TestCase
 
         $this->apply($travel, $participant, ['assignedRoomId' => 75]);
 
-        $this->assertSame(75, $participant->assignedRoomId);
+        $this->assertSame(74, $participant->assignedRoomId);
     }
 
     public function testDraftSkipsRoomThatIsUnknownToTravel(): void