This is key and I don’t think Signal shies away from this. You MUST trust the code you’re running. We know there are unofficial Signal builds. You must trust them. Why? Because think of it this way. You’re running a build of Signal, you type a messages. In code that text you type then gets run through Signal’s encryption. If you’re running a non-trustworthy build, they have access to the clear text before encryption, obviously. They can encrypt it twice, once with their key and once with yours, send it to a server, decrypt theirs and send yours on to it’s destination. (for example, there’s more ways than this).