Add Python provider with click and pretalx corpus

[markoa]

Pulls Python support forward from post-v0, using the same corpus shape as Ruby.

Canonical test repos

Python has several first-class project shapes (pip / Poetry / uv / Pipenv, pytest vs unittest, Django vs Flask vs FastAPI). Not every shape gets a remote corpus entry:

Shape	Covered by
Django + pip	focused python-django fixture
PEP 621 library + uv.lock	pallets/click
Production Django + uv	pretalx/pretalx
Poetry, Pipenv, setup.py, competing lockfiles, Flask server	unit tests
requirements.txt-only trees	not project roots (too many false positives)
conda	out of scope

This matches Ruby: ruby-rails fixture, ruby/rake library, basecamp/once-campfire app.

Provider

• Identity: pyproject.toml, setup.py, or Pipfile, merged when they coexist
• Managers from lockfiles / [tool.poetry|uv|pdm]; competing signals are an ambiguity
• Runtime: .python-version, .tool-versions, requires-python, with source/pointer from the declaring file
• Inferred commands: manager install, then pytest / unittest / manage.py test / Django/Flask server prefixed with uv run, poetry run, pipenv run, or pdm run when that manager is selected
• Configured tools stay tool.configured when no matching command exists
• GHA recognizes actions/setup-python, including GraalPy version-file pins
• Named pip install <package> in CI is tool provisioning, including option-prefixed forms such as uv --directory . pip install ruff

idea.md and plan.md record the decision to pull Python into v0 as milestone 8.

Accuracy and evidence-contract fixes

• Cites requirements.txt (including prefixed tools such as pytest-cov) instead of a fallback manifest
• Parses only install_requires / tests_require / setup_requires / extras_require in setup.py
• Treats [tool.poetry|uv|pdm] as the manager even when requirements.txt is also present
• Keeps requirements.txt dependencies scoped to pip so Poetry/uv/PDM/Pipenv do not claim packages that file never installs
• Unwraps nested runners so uv run python -m pytest is pytest
• Keeps relative local pip installs (../shared, packages/widget) as repository commands
• Discovers Django tests.py without treating helper modules such as testing.py as tests
• Preserves uv run --directory / -C / --project so CI commands are attributed to that working directory, including Semaphore
• Unwraps uv --directory packages/api run pytest and uv -C … tool run
• Consumes uv run value flags such as --env-file and --with-requirements
• Infers pip install -e . only for installable identities, not tool-only pyproject files
• Merges setup.py / Pipfile with pyproject.toml so build-system-only or tool-only pyproject files do not hide installable identity
• Cites Pipfile (not pyproject) when only Pipfile declares python_version
• Reads [tool.pdm.dev-dependencies] so pytest/Ruff declared there are not missed
• Limits prefix tool matching to pytest plugins; mypy-extensions is not tool.configured=mypy
• Accepts Ruby engine aliases and GraalPy pins in shared version-file parsing
• Does not treat pip/uv/Poetry -v as a version probe
• Treats pip install -c constraints.txt <pkg> as remote tool provisioning
• Skips named pip installs after uv/pip global options (uv --directory . pip install ruff, pip --index-url … install tox)
• Classifies Python installs in ClassifyManager so CI poetry install conflicts with inferred uv sync instead of emitting two preparation commands
• Skips virtualenvs via pyvenv.cfg or site-packages, not every directory named env
• Describes mixed manager ambiguities as competing signals unless every candidate is a lockfile
• Wraps inferred test/server commands in the selected manager environment
• Parses dotted TOML keys (project.name, project.dependencies) as nested tables
• Treats pytest plugins such as pytest-cov as pytest command signals
• Cites the selected manager signal (Pipfile) on inferred Pipenv installs
• Leaves expression-valued uv --directory on the enclosing project instead of fabricating a path
• Matches requires-python with PEP 440 comma bounds and ~= compatible releases
• Compares exact PEP 440 releases with zero padding so ==3.12 matches CI 3.12.0
• Leaves prerelease Python bounds such as >=3.13rc1 unevaluable instead of treating rc tokens as zero
• Activates extras and non-default dependency groups on inferred installs when pytest lives only there, including alongside requirements.txt
• Quotes pip extras (pip install -e '.[test]') so zsh nomatch does not fail the command
• Preserves setup.py extras_require extra names and does not treat tests_require as a main extra
• Honors Poetry optional = true extras via [tool.poetry.extras], optional groups with --with, and [tool.poetry.dev-dependencies]
• Ingests uv's deprecated [tool.uv] dev-dependencies as the default dev group
• Uses PDM -G for both extras and groups
• Keeps pip install --group and unresolved/$VAR wheel targets as visible CI commands
• Classifies poetry sync and pipenv sync as dependency installation
• Recognizes INI sections in setup.cfg and tox.ini for pytest, flake8, mypy, isort, and pylint
• Interprets only unqualified tox / tox run / nox as tests
• Unwraps poetry -C / pdm --project / uv --project globals before run

make check passes. requirements.txt pytest no longer produces poetry run pytest. ==3.12 folds CI 3.12.0 instead of conflicting. setup.cfg / tox.ini sections configure flake8, mypy, isort, and pylint.