I'd think a better idea would simply be to accept this as reality, and have a config entry or utility that lets you batch delete messages marked "ephemeral" (or better in this context, "unimportant").
The feature has two functions. The first is to decrease the severity of the consequences if a conversation partner's device falls into the wrong hands, say a government who wants to use chat messages as evidence, a corporate competitor who stole the phone, or just a friend who is rifling through your unlocked phone.
The other purpose is to make it easier to participate in a social contract where your chat history won't be kept around forever for all participants to dig up in the future. Yes, someone could modify the client code, or take screenshots, or do any number of things to preserve data. You still have to take care about what you send. But most people won't, because it is additional effort and generally people want to adhere to social contracts.
Security is never all or nothing. It is always about taking as many reasonable steps as you can to limit your risks.
Came here to say this but someone beat me to it. I imagine forging a screenshot to 'put words in someone's mouth' is hard to do though. You'd have to find a way of injecting words into the Signal app by messing with the code. You'd also have to use the correct font, make sure the metadata of the file is consistent, etc
Since there's no permalinks for a Signal message, you could forge anything you wanted, and you just have to get some dummy to believe the screenshot is an actual screenshot of a conversation. Treat screenshots of messenger apps with plenty of skepticism.
> This is not for situations where your contact is your adversary — after all, if someone who receives a disappearing message really wants a record of it, they can always use another camera to take a photo of the screen before the message disappears. However, this is a nice way to automatically save storage space on your devices and limit the amount of conversation history that remains on your device if you should find yourself physically separated from it.
> This is not for situations where your contact is your adversary — after all, if someone who receives a disappearing message really wants a record of it, they can always use another camera to take a photo of the screen before the message disappears.