Extract to files.py

app.py now contains two distinct types of logic: file system operations (list_files, read_file, index_folder) and AI operations (embedding, search, prompting). Mixing them in one file makes both harder to maintain — you have to read past embedding code to find file-reading code, and vice versa.

Splitting by responsibility gives each file a clear job:

• files.py handles everything related to reading files from disk.
• app.py handles everything related to the AI pipeline.

This separation makes the codebase easier to navigate and easier to extend. When you add support for a new file type in a later lesson, you'll edit only files.py. When you change how embeddings work, you'll edit only app.py.

In this chapter, you write files.py by copying the four file-related items out of app.py. The next chapter updates app.py to import from files.py instead.