fix: Mutate clipboard content when copying from a single table cell. (#7798)

* fix: Mutate clipboard content when copying from a single table cell.
closes #7794

* refactor

shared/editor/nodes/TableCell.ts

@@ -1,5 +1,5 @@
 import Token from "markdown-it/lib/token";
-import { NodeSpec } from "prosemirror-model";
+import { NodeSpec, Slice } from "prosemirror-model";
 import { Plugin } from "prosemirror-state";
 import { DecorationSet, Decoration } from "prosemirror-view";
 import { addRowBefore, selectRow, selectTable } from "../commands/table";
@@ -71,6 +71,35 @@ export default class TableCell extends Node {
     return [
       new Plugin({
         props: {
+          transformCopied: (slice) => {
+            // check if the copied selection is a single table, with a single row, with a single cell. If so,
+            // copy the cell content only – not a table with a single cell. This leads to more predictable pasting
+            // behavior, both in and outside the app.
+            if (slice.content.childCount === 1) {
+              const table = slice.content.firstChild;
+              if (
+                table?.type.spec.tableRole === "table" &&
+                table.childCount === 1
+              ) {
+                const row = table.firstChild;
+                if (
+                  row?.type.spec.tableRole === "row" &&
+                  row.childCount === 1
+                ) {
+                  const cell = row.firstChild;
+                  if (cell?.type.spec.tableRole === "cell") {
+                    return new Slice(
+                      cell.content,
+                      slice.openStart,
+                      slice.openEnd
+                    );
+                  }
+                }
+              }
+            }
+
+            return slice;
+          },
           handleDOMEvents: {
             mousedown: (view, event) => {
               if (!(event.target instanceof HTMLElement)) {