Don't delete an attachment dropped onto one that can't form a gallery

src/editor/attachments/drag_and_drop.js

@@ -277,15 +277,18 @@ export class AttachmentDragAndDrop {
     if (!targetNode || !$isActionTextAttachmentNode(targetNode)) return
     if (draggedNode.is(targetNode)) return
 
+    // Resolve the gallery before detaching: the drop target matches any
+    // previewable attachment, but galleries only accept images, so removing
+    // first deleted PDFs and videos dropped onto another attachment.
+    const gallery = $findOrCreateGalleryForImage(targetNode)
+    if (!gallery) return
+
     draggedNode.remove()
 
-    const gallery = $findOrCreateGalleryForImage(targetNode)
-    if (gallery) {
-      if (position === "before") {
-        targetNode.insertBefore(draggedNode)
-      } else {
-        targetNode.insertAfter(draggedNode)
-      }
+    if (position === "before") {
+      targetNode.insertBefore(draggedNode)
+    } else {
+      targetNode.insertAfter(draggedNode)
     }
   }
 

test/browser/tests/attachments/attachment_drag_and_drop.test.js

@@ -146,6 +146,22 @@ test.describe("Attachment Drag and Drop", () => {
 
       await assertGalleryWithImages(editor, 3)
     })
+
+    test("drag a previewable non-image onto another keeps both", async ({ page, editor }) => {
+      await editor.uploadFile("test/fixtures/files/dummy.pdf")
+      await editor.send("Enter")
+      await editor.uploadFile("test/fixtures/files/dummy.pdf")
+      await waitForUploadsComplete(page, editor)
+      await expect(page.locator("figure.attachment")).toHaveCount(2)
+
+      await simulateDragByIndex(page, 1, 0, "onto")
+      await editor.flush()
+
+      // Galleries only take images, so this drop cannot be honoured. It should
+      // leave the document alone rather than swallow the dragged attachment.
+      await assertNoGallery(page)
+      await expect(page.locator("figure.attachment")).toHaveCount(2)
+    })
   })
 
   test.describe("Within-gallery reorder", () => {