This is the full plugin for CodeMirror Speak-and-Spell for CodeMirror 5.

It allows native browser/OS features such as spell checking,

speech-to-text, AI-assisted writing/rewriting, and other text

replacements to work with CodeMirror.
It does this by intercepting the beforeinput events emitted by the

browser before any text would be inserted or replaced, canceling the

change, and then replaying the same change using CodeMirror's API.
By doing it this way, we avoid the thrashing that occurs with

CodeMirror's own attempts at supporting these features. Normally,

CodeMirror will listen for an input change and then wait 40ms before

relaying changes back into CodeMirror, but in practice this doesn't

consistently work. It's okay on Firefox, but has a tendency to undo

replaced changes on Chrome and Safari. Taking the browser's DOM

manipulations out of the equation removes the source of this problem

entirely.
A sample file has been provided to experience the plugin on different

browsers.

Tested Chrome, Firefox, and Safari with both the sample page and with

the plugin used in Review Board.
My tests involved the following on each:

General typing and text formatting using Review Board's toolbar.
Inline spelling/grammar suggestions with text replaced.
Dialog-based spelling/grammar suggestions with replacements.
Safari's text transformations (Capitalize, Make Upper Case, Make Lower Case).
AI-assisted writing, re-writing, and summarizations.
Speech-to-text.

These were tested at various places within a test document. I checked

that this all worked regardless of where the cursor was.
Unlike with default behavior, I didn't see any document thrashing at any

point, or any data loss.