How do you let the system know that these bricks are a dictionary?

These bricks returned an error because File 1 returns a text instead of a dictionary.

Check this:

Yes, it replied false.

Another one does too.

have you tried this?

Learn JSON

Make a Dictionary will return a Dictionary.
But you connect it with File.SaveFile, the text socket need a String, AI will change Dictionary to String/JSON.
When you read from the file, you will get a String, you need to use Web.JsonTextDecode to convert String/JSON to dictionary.

Why not use a csv for read write and convert csv to dictionary when needed ?