Signal has a PIN, too. If that's required for the transfer, then it would prevent this in the case of brief, surreptitious access. A hostage scenario is impossible
> There are many cases where an attacker can access a device for a short time and/or without the owner realizing that the phone was tampered with.
This is what you originally responded to. I paraphrased it. The "heavy lifting" meme that you've employed is rarely more than a shallow dismissal. Be better.