Initialise FileUploadField only on the newly added collection item

'ea.collection.item-added' was re-running the document-wide query for file upload inputs, which double-bound the change/click handlers on every already-processed field and could prevent the new field from displaying selected files reliably (Bootstrap markup variations exposed this further).

Scope the query to event.detail.newElement, and guard each input with a data-ea-fileupload-initialized flag so re-entry is safe.

Fixes #6637

Author: lacatoire

assets/js/field-file-upload.js

@@ -1,13 +1,22 @@
 import { toggleVisibilityClasses } from './helpers';
 
-const eaFileUploadHandler = (event) => {
-    document.querySelectorAll('.ea-fileupload input[type="file"]').forEach((fileUploadElement) => {
+const initFileUploadFields = (root) => {
+    root.querySelectorAll('.ea-fileupload input[type="file"]').forEach((fileUploadElement) => {
+        if (fileUploadElement.dataset.eaFileUploadInitialized === '1') {
+            return;
+        }
+        fileUploadElement.dataset.eaFileUploadInitialized = '1';
         new FileUploadField(fileUploadElement);
     });
 };
 
-window.addEventListener('DOMContentLoaded', eaFileUploadHandler);
-document.addEventListener('ea.collection.item-added', eaFileUploadHandler);
+window.addEventListener('DOMContentLoaded', () => initFileUploadFields(document));
+document.addEventListener('ea.collection.item-added', (event) => {
+    // only initialise the file upload fields contained in the newly added collection item:
+    // re-running the query on the whole document would re-attach listeners to already
+    // processed fields and double-fire their handlers (see #6637).
+    initFileUploadFields(event.detail.newElement ?? document);
+});
 
 class FileUploadField {
     #fieldContainerElement;