AI agent guidance

CPython has a policy on the use of AI tools. All use of AI tools and agents when working on or interacting with CPython must follow it.

[!important] Primary directive: Read the policy before making or proposing any changes.

When acting on this repository, apply the policy's core principles:

• Consider whether the change is necessary.
• Make minimal, focused changes.
• Follow existing coding style and patterns.
• Write tests that exercise the change.
• Keep backwards compatibility with prior releases in mind.