The em-dash=LLM thing is so crazy. For many years Microsoft Word has AUTOCORRECTED the typing of a single hyphen to the proper syntax for the context -- whether a hyphen, en-dash, or em-dash.

I would wager good money that the proliferation of em-dashes we see in LLM-generated text is due to the fact that there are so many correctly used em-dashes in publicly-available text, as auto-corrected by Word...

Which would matter but the entry box in no major browser do was this.

The HN text area does not insert em-dashes for you and never has. On my phone keyboard it's a very lot deliberate action to add one (symbol mode, long press hyphen, slide my finger over to em-dash).

The entire point is it's contextual - emdashes where no accomodations make them likely.