fix: reconcile remaining children to prevent double removal (#22566)

Fixes #22565

Author: heruan

flow-server/src/main/java/com/vaadin/flow/component/ComponentEffect.java

@@ -316,8 +316,13 @@ private static <T> void updateByChildSignals(
 
             // Use LinkedList for order
             Element actualChild = remainingChildren.pollFirst();
-            if (!remainingChildrenSet.contains(actualChild)) {
-                continue; // skip children that have been removed already
+            // Skip children that have been removed already
+            while (actualChild != null
+                    && !remainingChildrenSet.contains(actualChild)) {
+                actualChild = remainingChildren.pollFirst();
+            }
+            if (actualChild == null) {
+                continue;
             }
             if (!Objects.equals(actualChild, expectedChild)) {
                 /*

flow-server/src/test/java/com/vaadin/flow/component/ComponentEffectTest.java

@@ -416,30 +416,35 @@ public void bindChildren_removeItem_parentUpdated() {
         runWithFeatureFlagEnabled(() -> {
             ListSignal<String> taskList = new ListSignal<>(String.class);
             taskList.insertFirst("first");
+            taskList.insertLast("middle");
             taskList.insertLast("last");
             TestLayout parentComponent = new TestLayout();
             new MockUI().add(parentComponent);
 
             ComponentEffect.bindChildren(parentComponent, taskList,
                     valueSignal -> new TestComponent(valueSignal.value()));
 
-            assertEquals("Parent component children count is wrong", 2,
+            assertEquals("Parent component children count is wrong", 3,
                     parentComponent.getComponentCount());
 
             List<TestComponent> children = parentComponent.getChildren()
                     .map(TestComponent.class::cast).toList();
 
             taskList.remove(taskList.value().get(0));
 
-            assertEquals("Parent component children count is wrong", 1,
+            assertEquals("Parent component children count is wrong", 2,
                     parentComponent.getComponentCount());
+            assertEquals("middle", ((TestComponent) parentComponent
+                    .getChildren().toList().get(0)).getValue());
             assertEquals("last", ((TestComponent) parentComponent.getChildren()
-                    .toList().get(0)).getValue());
+                    .toList().get(1)).getValue());
 
             assertEquals(1, children.get(0).attachCounter);
             assertEquals(1, children.get(0).detachCounter);
             assertEquals(1, children.get(1).attachCounter);
             assertEquals(0, children.get(1).detachCounter);
+            assertEquals(1, children.get(2).attachCounter);
+            assertEquals(0, children.get(2).detachCounter);
         });
     }