Short version: I measured what a single paste costs an AI agent. A 2,348-line source file is 40,324 tokens, one fifth of a 200,000 token window, gone in one keystroke. The path to that same file is 19 tokens. Four pastes like that and the agent starts forgetting the instructions you gave it an hour earlier. At the end I show what I did about it.
The session that gets dumber
You know the shape of this even if you have never named it.
You start a session in the morning. You explain the project, the constraints, the two things the agent must never touch. It works. The answers are sharp, it remembers the schema, it follows your conventions.
Two hours later the same agent suggests exactly the thing you ruled out at the start. It re-reads a file it already read. It asks you which framework the project uses. Nothing crashed, nothing errored, the model is the same model. It just got dumber.
