Bug: Undo History Not Working for Accept Changes in UnifiedMergeView

Description

When using unifiedMergeView with mergeControls: true, the undo history functionality (Ctrl+Z/Cmd+Z) only works for rejected changes but not for accepted changes. The expected behavior is that both accept and reject operations should be undoable.

Steps to Reproduce

1. Create a basic setup with unifiedMergeView:

"use client";
import React, { useEffect, useRef } from "react";
import { EditorView, keymap  } from "@codemirror/view";
import { unifiedMergeView } from "@codemirror/merge";
import { javascript } from "@codemirror/lang-javascript";
import { oneDark } from "@codemirror/theme-one-dark";
import { defaultKeymap, history, historyKeymap } from "@codemirror/commands";

export default function DemoMergeIssue() {
  const editorRef = useRef(null);
  const commonExtensions = [
    javascript({ jsx: true, typescript: true }), 
    oneDark,
    history(),
    keymap.of(defaultKeymap),
    keymap.of(historyKeymap),
  ];
  useEffect(() => {
    if (editorRef.current) {

      // Create a unified merge view.
      const view = new EditorView({
        doc: "console.log('Modified Code');",
        extensions: [
          ...commonExtensions,
          oneDark,
          javascript(),
          unifiedMergeView({
            original: "console.log('Original Code');",
            highlightChanges: true,
            mergeControls: true,
          }),
        ],
        parent: editorRef.current,
      });
      return () => view.destroy();
    }
  }, []);

  return (
    <div
      ref={editorRef}
      style={{
        height: "400px",
        border: "1px solid #ccc",
        borderRadius: "4px",
        margin: "1rem 0",
      }}
    />
  );
}
});

1. Click the "Accept" button in merge controls
2. Try to undo the accept operation with Ctrl+Z/Cmd+Z
3. Expected: Changes are undone, Actual: Nothing happens
4. Click the "Reject" button in merge controls
5. Try to undo the reject operation with Ctrl+Z/Cmd+Z
6. Expected: Changes are undone, Actual: Changes are undone successfully

Analysis

The issue appears to be related to how the unified merge view handles history states for accept operations. While reject operations properly integrate with the history extension, accept operations seem to bypass the history mechanism.

Environment

    "@codemirror/commands": "^6.8.0",
    "@codemirror/lang-javascript": "^6.2.3",
    "@codemirror/merge": "^6.8.0",
    "@codemirror/state": "^6.5.2",
    "@codemirror/theme-one-dark": "^6.1.2",
    "@codemirror/view": "^6.36.3",

Start by running the provided unifiedMergeView reproduction with mergeControls and the history extension, then trace how Accept and Reject dispatch their changes. Confirm the behavior against the stated undo expectations and identify the relevant integration point before adding a regression test; done means accepted changes can be undone like rejected changes.