Python: Establish canonical coding standards and Copilot review guidance #9636

Maintainer-owned issue. Community contributors: please do not pick up or start implementing this issue.

Category

Documentation

Problem

Python engineering guidance is duplicated across python/CODING_STANDARD.md, nested agent skills, and a path-specific Copilot instruction stored outside GitHub's documented repository-root discovery location. The copies disagree on typing suppressions, fixtures, inheritance, performance guidance, and public API ergonomics.

Evidence

• python/CODING_STANDARD.md mixes durable engineering rules with package layout, installation, and workflow-specific guidance.
• python/.github/skills/python-development/SKILL.md duplicates and conflicts with the coding standard.
• python/.github/instructions/python.instructions.md is nested below python/ rather than .github/instructions/ at the repository root.
• GitHub Copilot code review supports repository-root path-specific instructions and reads them from the pull request head branch.

Desired Outcome

Make python/CODING_STANDARD.md the canonical MUST/SHOULD/MAY standard, keep task-specific workflow details in the owning skills, align sample/testing guidance, and add a concise root .github/instructions/python.instructions.md file so Copilot code review loads the Python standards out of the box.

Language

Python

Acknowledgements

• I searched existing issues and did not find a duplicate.
• I will wait for explicit maintainer agreement before starting implementation of a non-trivial change.

Ownership: Core maintainers only; not available for community pickup.