Do we still need program source code?

One idea would be not to have the code as the result of your prompt, but the result itself.

Why not to let the environment do everything integrated, according to your prompt?

Else you have the disconnect between the prompt and the generated code. The generated code need to run somewhere, need to be integrated and maintained.

That stringdiff function is a part of the bigger environment.

So ultimately you should just be able to request your assistant to make sure all the work assigned to you is done properly, and then the assistant should report to the original requestor of the work done.

At least for now the source code is the contract with the machine, to know what you really expect it to do. But I agree that more "freeform" languages (e.g. JS) could be less useful in an LLM world.