If your code is released with no license, it should be fair to assume free use. But if it is licensed, tools like Copilot should be forced to respect that.
Legally? The opposite is true. Source-available is not open source, and is emphatically not public domain.
There's a reason that StackOverflow and all the other code bins have legal agreements that you are notified of when using them.
Yes.
Are you allowed to remember it?
Yes.
Are you allowed to use similar patterns / naming conventions / algorithms when your are trying to solve your own unique problems?
…I hope so, or you won’t be much value to your employer.
That’s all an AI does. Same thing as you, it’s just more efficient (in some ways).