[amuraru]

Description

Discover the CI test matrix from the official Python release-cycle JSON feed used by the Python Developer's Guide, rather than maintaining a fixed list.

• Test every bugfix and security Python release on Ubuntu and macOS; exclude prereleases and EOL releases.
• Validate the feed, retry network failures up to three attempts, and fail discovery explicitly rather than silently skipping tests.
• Upload coverage from the newest discovered stable version.
• Raise the package minimum to Python 3.11, update classifiers through 3.15, and align Black's target. Python 3.10 reached EOL on October 1, 2026.
• Document that future matrix updates are automatic, while package minimum-version and classifier changes remain explicit release decisions.

This addresses the Python support-policy mismatch exposed by #228: its coverage 7.17.0 update requires Python 3.11 or newer. This PR does not change those dependency pins.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring
• Performance improvement
• Test improvement

Testing

• Tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have tested the changes manually

Validation uses the project's existing development dependencies in a dedicated virtual environment, on Python 3.13:

• python -m pytest tests/ -q --cov=himl --cov-report=term-missing --cov-fail-under=80 — passed: 244 tests, 92.51% coverage.
• python -m flake8 . --count --select=E9,F63,F7,F82 --show-source --statistics — passed: zero errors.
• python -m flake8 .github/scripts/python_versions.py tests/test_python_versions.py — passed.
• python -m flake8 . --count --exit-zero --max-complexity=10 --max-line-length=120 --statistics — completed with four existing advisory warnings in unchanged files.
• python -m mypy himl/ .github/scripts/python_versions.py --ignore-missing-imports — passed: 17 source files.
• python -m black --check .github/scripts/python_versions.py tests/test_python_versions.py — passed.
• actionlint -shellcheck='' .github/workflows/ci.yaml — passed.
• python .github/scripts/python_versions.py — passed against the live official feed: versions 3.11–3.15, latest 3.15.
• python -m build --outdir "$ARTIFACT_DIR" — passed for the final commit; ARTIFACT_DIR points to a session-local build output directory.
• python -m twine check "$ARTIFACT_DIR"/* — passed for both the final source distribution and wheel.

The new tests cover stable-release filtering, numeric version sorting, malformed/empty data, network retries, exhausted retries, invalid JSON, and GitHub Actions outputs.

The first GitHub Actions run passed all 15 jobs: live discovery, all ten Python 3.11–3.15 Ubuntu/macOS matrix jobs, security, package build, Docker, and integration tests.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

Additional Notes

• Breaking support change: new releases require Python 3.11 or newer.
• CI now depends on the availability and schema of the official feed. New Python releases can introduce dependency incompatibilities without a repository commit; this is intentional for an always-current matrix.
• Full actionlint .github/workflows/ci.yaml reports the existing ShellCheck SC2086 warning for an unquoted $GITHUB_OUTPUT in the unchanged pip-cache step. Workflow validation passes with ShellCheck disabled; the newly added shell command quotes its output path.
• No dependent downstream changes are required.