Bug: Speech-to-text (dictation) on iOS deletes words after completion

[moughxyz]

Please see video.

Steps to replicate:

1. On iOS, open https://playground.lexical.dev/
2. Delete all the filler text
3. Hit the system microphone button on the keyboard (not lexical's microphone button)
4. Begin dictating, adding 2 sentences or so.
5. After you're done, hit the microphone button again to stop dictation.

At this point, you'll see a good amount of words disappear from the editor.

speech-bug-2.mov

As a first step I'm just opening this ticket to increase exposure in case someone might obviously know what's wrong, before investigating deeper.

Via chatgpt, speech to text uses composition events compared to traditional keyboard input:

•	Dictation uses composition events to handle intermediate input. These include:
•	   compositionstart: Marks the beginning of dictated input.
•	   compositionupdate: Fires as the text updates.
•	   compositionend: Finalizes the text input.
•	Keyboard input usually doesn’t rely on compositionupdate.

https://github.com/facebook/lexical/blob/main/packages/lexical/src/LexicalEvents.ts#L899

[moughxyz]

This seems to also affect input with diacritic letters, which also uses composition. Characters are being deleted. Report from a user:

it's most likely because these are often typed with dead keys (i.e. two keystrokes). If typed with a single keystroke, they remain, if typed with a dead ˇ , they disappear. Tried a few random ones and can reproduce consistently
funny thing is that in fact the character does not appear alone, instead, the sequence appears (and vanishes) as two characters, like ˇČ

Explanation via chatgpt again (sorry):

Why Composition Events Are Used

When typing diacritic letters:
	1.	The user usually starts with a “dead key” (e.g., ´, ^) or a specific key combination (e.g., Alt+e).
	2.	The browser enters a “composition mode” to wait for the next key input.
	3.	Once the user types the base letter (e.g., e), the browser combines the diacritic with the base letter and exits composition mode.

This process involves multiple stages, which the browser tracks using composition events.