Bug: Accepting the correction replaces the flagged word with the whole sentence

**Describe the bug**
When I accept the suggestion from the Harper menu in my browser, it does not just correct the selected word, it replaces the highlighted word with the whole sentence. This is happening in Gmail on Firefox with the browser extension installed.

**To Reproduce**
Steps to reproduce the behavior:
1. In Gmail on Firefox, type a sentence with a typo
2. Click on the suggested word
3. Word is replaced with full sentence
4. See error

**Expected behavior**
I expected only the word to be replaced like in other sites.

**Screenshots**

**Platform**
Firefox, only in Gmail.

Start by reproducing the correction flow in Gmail on Firefox with the Harper browser extension, following the listed steps and comparing it with another site where correction works. Trace the extension's handling of the selected word and sentence in that environment. Done means accepting a suggestion replaces only the flagged word in Gmail on Firefox.

Written by the indexing model from the issue text.