Replacement of text shows up as insertion instead

[wjiayis]

Describe the bug
When I want to paraphrase a sentence, although the diff shows some changes, it is inserted rather than replaced.

To Reproduce

1. Highlight a sentence.
2. Click "Add to chat".
3. Ask LLM to paraphrase it.
4. Click "Insert".

Expected behavior
I'd prefer if there's a separate button "Replace" to replace the original text with the paraphrased text.

Screenshots
https://github.com/user-attachments/assets/b6bd1be3-0289-4ac6-bf57-6591838a01a2