Report a bad ini core value as a handled error

[VXNCXNX]

A bad value in the ini [tox] core section exits with a raw traceback, while the same value in pyproject.toml is already reported properly.

$ printf '[tox]\nmin_version = notaversion\n' > tox.ini && tox l
  File ".../packaging/version.py", line 452, in __init__
    raise InvalidVersion(f"Invalid version: {version!r}")
packaging.version.InvalidVersion: Invalid version: 'notaversion'

The TOML path, same input, unchanged by this PR:

$ printf '[tool.tox]\nmin_version = "notaversion"\n' > pyproject.toml && tox l
ROOT: HandledError| failed to load core.min_version: Invalid version: 'notaversion'

After:

ROOT: HandledError| failed to load tox.min_version: Invalid version: 'notaversion'

requires = ===bad!!! and env_list = {py39,py310 (unbalanced brace) were tracebacks too, and are now handled the same way.

The fix

IniLoader.build called self.to(...) unguarded. TomlLoader.build already wraps the identical call and re-raises as HandledError, so this mirrors it, including letting HandledError and Skip through untouched.

Why the guard is narrow

The wrap only applies to the core section. My first attempt covered every section and broke 6 existing tests, because two paths deliberately let raw exceptions through:

• testenv values, where tox c renders the exception inline as # Exception: ... (test_config_bad_dict, test_config_bad_bool and friends)
• the CLI config file, loaded with conf is None

Those are existing behaviour I did not want to change, so the condition is conf is None or args.env_name is not None to bypass. Core values are the case with no handling at all, because they are loaded before any guard is in place.

Verification

test_ini_core_bad_value_is_handled_error in tests/config/source/test_discover.py, parametrised over min_version, requires and env_list. It asserts no unhandled exception leaks, so it fails on the actual symptom rather than on a message string.

Reverting only the guard condition to always bypass fails it as an assertion:

>       assert leaked is None, f"unhandled {type(leaked).__name__}: {leaked}"
E       AssertionError: unhandled InvalidVersion: Invalid version: 'notaversion'
E       AssertionError: unhandled InvalidRequirement: Expected package name at the start of dependency specifier
E       AssertionError: unhandled ValueError: {py39

pytest tests/config/ is 6644 passed, 2 skipped. tests/config/cli/test_argcomplete.py is excluded because argcomplete is not installed here; it fails to collect identically on a clean checkout.

Disclosure: written with AI assistance (Claude Code). I reproduced the traceback and the TOML contrast at the CLI, confirmed the narrow guard is required by removing it and watching 6 tests break, and ran the mutation check myself.