fix: use PDM interpreter in generation and formatting scripts (#1277)

## ℹ️ Description
`pdm run generate-artifacts` could fail while creating the default
config when the shell's `python` differed from PDM's selected
interpreter. For example, Python 3.13 on PATH loaded dependencies from
`__pypackages__/3.12`, causing `ModuleNotFoundError:
pydantic_core._pydantic_core`.

Use PDM's interpreter consistently for config generation and Python
post-formatting. This fix is independent of login-entry PR #1276.

## 📋 Changes Summary

- Replace the shell-based config generator with a Python script that
invokes the CLI through `sys.executable`.
- Split `format:py` into a PDM composite so the Python post-formatter
also uses PDM's interpreter.
- Add an integration regression test that regenerates the exact config
snapshot with an unusable Python executable on PATH.
- Preserve supported Python versions, CLI generation behavior, and
generated artifacts. No dependency or user-configuration changes; no
documentation updates needed.

Validation: `pdm run format`, `pdm run lint`, `pdm run test`, `pdm run
generate-artifacts`, and generated-artifact verification passed. The
generator was also verified locally with PDM selecting Python 3.12 while
shell Python resolves to 3.13.

### ⚙️ Type of Change

- [x] 🐞 Bug fix (non-breaking change which fixes an issue)
- [ ] ✨ New feature (adds new functionality without breaking existing
usage)
- [ ] 💥 Breaking change (changes that might break existing user setups,
scripts, or configurations)

## ✅ Checklist

- [x] I have reviewed my changes to ensure they meet the project's
standards.
- [x] I have tested my changes and ensured that all tests pass (`pdm run
test`).
- [x] I have formatted the code (`pdm run format`).
- [x] I have verified that linting passes (`pdm run lint`).
- [x] I have updated documentation where necessary (no documentation
changes required).

By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice.


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Chores**
* Improved the configuration generation workflow by using the active
Python environment directly.
* Split Python formatting into separate automatic formatting and
follow-up processing steps for more consistent results.

* **Tests**
* Added integration coverage to verify configuration generation works
reliably even when conflicting Python executables are present on the
system path.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

pyproject.toml

@@ -93,7 +93,7 @@ debug = "python -m pdb -m kleinanzeigen_bot"
 
 # build & packaging
 generate-schemas = "python scripts/generate_schemas.py"
-generate-config = { shell = "python -c \"from pathlib import Path; Path('docs/config.default.yaml').unlink(missing_ok=True)\" && python -m kleinanzeigen_bot --config docs/config.default.yaml create-config" }
+generate-config = "python scripts/generate_config.py"
 generate-readme-commands = "python scripts/generate_readme_commands.py"
 generate-artifacts = { composite = ["generate-schemas", "generate-config", "generate-readme-commands"] }
 compile.cmd = "python -O -m PyInstaller pyinstaller.spec --clean --workpath .temp"
@@ -107,7 +107,9 @@ deps                = "pdm list --fields name,version,groups"
 
 # format & lint
 format        = { composite = ["format:py", "format:yaml"] }
-"format:py"   = { shell = "autopep8 --recursive --in-place scripts src tests --verbose && python scripts/post_autopep8.py scripts src tests" }
+"format:py"   = { composite = ["format:autopep8", "format:post-autopep8"] }
+"format:autopep8" = "autopep8 --recursive --in-place scripts src tests --verbose"
+"format:post-autopep8" = "python scripts/post_autopep8.py scripts src tests"
 "format:yaml" = "yamlfix scripts/ src/ tests/"
 
 lint = { composite = ["lint:ruff", "lint:mypy", "lint:pyright", "lint:actions"] }

scripts/generate_config.py

@@ -0,0 +1,25 @@
+# SPDX-FileCopyrightText: © Jens Bergmann and contributors
+# SPDX-License-Identifier: AGPL-3.0-or-later
+# SPDX-ArtifactOfProjectHomePage: https://github.com/Second-Hand-Friends/kleinanzeigen-bot/
+"""Regenerate the default config using the interpreter selected by PDM."""
+
+import subprocess  # noqa: S404
+import sys
+from pathlib import Path
+
+
+def main() -> None:
+    """Replace the default config snapshot through the CLI with the current interpreter."""
+    repo_root = Path(__file__).resolve().parent.parent
+    config_path = repo_root / "docs/config.default.yaml"
+    config_path.unlink(missing_ok = True)
+    subprocess.run(  # noqa: S603 trusted, static command arguments
+        [sys.executable, "-m", "kleinanzeigen_bot", "--config", str(config_path), "create-config"],
+        cwd = repo_root,
+        check = True,
+        timeout = 60,
+    )
+
+
+if __name__ == "__main__":
+    main()

tests/integration/test_generate_config.py

@@ -0,0 +1,60 @@
+# SPDX-FileCopyrightText: © Jens Bergmann and contributors
+# SPDX-License-Identifier: AGPL-3.0-or-later
+# SPDX-ArtifactOfProjectHomePage: https://github.com/Second-Hand-Friends/kleinanzeigen-bot/
+"""Regression coverage for config generation with a different Python on PATH."""
+
+import json
+import os
+import shutil
+import subprocess  # noqa: S404
+import sys
+from pathlib import Path
+
+import pytest
+
+
+@pytest.mark.itest
+def test_generate_config_uses_current_interpreter(tmp_path:Path) -> None:
+    repo_root = Path(__file__).resolve().parent.parent.parent
+    pdm_path = shutil.which("pdm")
+    assert pdm_path is not None, "PDM is required to test the generate-config task"
+    # Expose test dependencies only to the task; PDM itself may use a different Python.
+    python_path = os.pathsep.join(str(Path(path).resolve()) for path in sys.path if path)
+    (tmp_path / "pyproject.toml").write_text(
+        (repo_root / "pyproject.toml").read_text(encoding = "utf-8")
+        + f"\n[tool.pdm.scripts._]\nenv = {{ PYTHONPATH = {json.dumps(python_path)} }}\n",
+        encoding = "utf-8",
+    )
+    (tmp_path / ".pdm-python").write_text(sys.executable, encoding = "utf-8")
+    (tmp_path / "pdm.toml").write_text("[python]\nuse_venv = false\n", encoding = "utf-8")
+    script_path = tmp_path / "scripts/generate_config.py"
+    script_path.parent.mkdir()
+    script_path.write_bytes((repo_root / "scripts/generate_config.py").read_bytes())
+    config_path = tmp_path / "docs/config.default.yaml"
+    config_path.parent.mkdir()
+    config_path.write_text("stale config", encoding = "utf-8")
+
+    # A PATH-resolved Python cannot run; the selected interpreter must be used instead.
+    bin_path = tmp_path / "bin"
+    bin_path.mkdir()
+    for name in ("python", "python.exe"):
+        wrong_python = bin_path / name
+        wrong_python.write_text("invalid executable", encoding = "utf-8")
+        wrong_python.chmod(0o755)
+
+    result = subprocess.run(  # noqa: S603 trusted test command
+        [pdm_path, "run", "generate-config"],
+        env = {
+            **{key: value for key, value in os.environ.items() if key != "PYTHONPATH"},
+            "PATH": str(bin_path),
+            "PDM_CHECK_UPDATE": "false",
+        },
+        cwd = tmp_path,
+        check = False,
+        capture_output = True,
+        text = True,
+        timeout = 60,
+    )
+
+    assert result.returncode == 0, result.stderr
+    assert config_path.read_bytes() == (repo_root / "docs/config.default.yaml").read_bytes()