Every prompt adds unrequested state

1. Check the problem

Left unconstrained, the model defaults to adding everything that might be useful. Write it once in AGENTS.md: don't add new state, dependencies, or files unless explicitly asked. Reference it every session.

2. Use the prompt

Constraint for this whole session: don't add new state, new dependencies, new files, or new abstractions unless I explicitly ask. Implement exactly what I request and nothing more. If you think something extra is needed, propose it first and wait for my yes.

3. Verify the fix

Review the proposed diff, run the relevant checks and exercise the original failing flow before merging.