[lukeschlather]

Are there any comparable hosted messaging services that don't do this?

[s09dfhks]

signal/telegram

[tialaramex]

Signal actually does optionally offer previews for a handful of services, and they really jump through some hoops to make that safer:

https://support.signal.org/hc/en-us/articles/360022474332-Li...

The service being previewed doesn't know who you are because Signal acts as a proxy, Signal doesn't know what you previewed on that service because their client deliberately sends overlapping Range requests so that the preview size is rounded.

[duskwuff]

Telegram does crawl links sent in non-encrypted messages. Links in secret chats are left alone, though.

[brennebeck]

Probably Signal.