Diff view not shown when Cursor agent chat edits cells (works for Cmd-K only)

### Describe the bug When Cursor's **agent chat** modifies notebook cells, no visual diff is shown comparing the proposed change against the existing code. The diff view works correctly for **Cmd-K inline edits** but is absent for agent-driven edits. ### Steps to reproduce 1. Open a `.py` marimo notebook in Cursor 2. Use Cursor's **agent chat** to propose a change to a cell — no diff shown ✗ 3. Use **Cmd-K** on a cell to propose an inline edit — diff shown correctly ✓ ### Expected behavior A visual diff of the proposed change vs. existing cell code should appear regardless of whether the edit comes from agent chat or Cmd-K. ### Environment - Cursor (latest) - marimo VS Code Extension 0.11.4 - macOS 15 (Apple Silicon)