Aider has a command to add files to the prompt. For files that are not added, it uses tree-sitter to extract a high-level summary. So for a `.env`, it will mention to the LLM the fact that the file exists, but not what is in it. If the model thinks it needs to see that file, it can request it, at which point you receive a prompt asking whether it's okay to make that file available.

It's a very slick workflow.

You can use an .aiderignore file to ensure aider doesn't use certain files/dirs/etc. It conforms to the .gitignore spec.