Add AI-disclosure and quality requirements to the contribution guidelines

CONTRIBUTING.md

@@ -9,6 +9,37 @@ The following is a short step-by-step rundown of what one typically would do to
 - Feel free to add yourself to AUTHORS file.
 - Create a pull request.
 
+## Quality expectations
+
+Contributions must be made with care and meet the quality bar of the surrounding code.
+That means a change should not leave GitPython worse than it was before: it should be
+readable, maintainable, tested where practical, documented and consistent with the
+existing style and behavior.
+
+A contribution that works only narrowly but lowers the quality of the
+codebase may be declined. The maintainers may not always be able to provide
+detailed feedback.
+
+## AI-assisted contributions
+
+If AI edits files for you, disclose it in the pull request description and commit
+metadata. Prefer making the agent identity part of the commit, for example by using
+an AI author such as `$agent $version <ai-agent@example.invalid>` or a co-author via
+a `Co-authored-by: <agent-identity>` trailer.
+
+Agents operating through a person's GitHub account must identify themselves. For
+example, comments posted by an agent should say so directly with phrases like
+`AI agent on behalf of <person>: ...`.
+
+Fully AI-generated comments on pull requests or issues must also be disclosed.
+Undisclosed AI-generated comments may lead to the pull request or issue being closed.
+
+AI-assisted proofreading or wording polish does not need disclosure, but it is still
+courteous to mention it when the AI materially influenced the final text.
+
+Automated or "full-auto" AI contributions without a human responsible for reviewing
+and standing behind the work may be closed.
+
 ## Fuzzing Test Specific Documentation
 
 For details related to contributing to the fuzzing test suite and OSS-Fuzz integration, please