Validate positive CLI numeric options consistently (closes #15)

[dchaudhari7177]

Closes #15.

The two positive-integer options failed differently for the same class of bad input: --workers 0 was swallowed by args.workers or defaults.workers and silently fell back to the default worker count, while --max-complexity 0 reached AnalyzerConfig and surfaced as a ValueError traceback.

What changed

A small reusable argparse type:

def _positive_int(value: str) -> int:
    try:
        number = int(value)
    except ValueError:
        raise argparse.ArgumentTypeError(f"expected an integer, got {value!r}") from None
    if number < 1:
        raise argparse.ArgumentTypeError(f"must be at least 1, got {number}")
    return number

Applied to --workers and --max-complexity. Both now fail as argparse usage errors with exit code 2:

code-health scan: error: argument --workers: must be at least 1, got 0

It also catches non-integers with a clearer message than argparse's default invalid int value.

The or in main() is now an explicit is None check. _positive_int means 0 can't reach it any more, so this is belt-and-braces — but the or was the bug, and spelling out that None (option omitted) is the only fallback case keeps it from coming back.

AnalyzerConfig.__post_init__ validation is deliberately untouched: CLI validation is additive and direct API callers keep their own guard. There's a test pinning that, since "moved the check to the CLI" would be the tempting wrong refactor.

No dependency added.

Tests

10 added to tests/test_cli.py, parametrized over both option names:

• 0 and -1 → exit code 2, stderr names the option and says "must be at least 1"
• non-integer input → exit code 2, "expected an integer"
• a valid explicit value (--workers 2, --max-complexity 1) still scans and returns 0
• omitting both keeps workers is None and max_complexity == AnalyzerConfig().max_complexity
• AnalyzerConfig(workers=0) / AnalyzerConfig(max_complexity=0) still raise ValueError

Red-before-green: with git stash push -- src/code_health/cli.py, all 6 rejection tests fail against pristine code.

Gate

Ran the full local gate from CONTRIBUTING on Windows / Python 3.12:

• pytest — 24 passed, coverage 92.93% (threshold 85%)
• ruff check . — clean
• ruff format --check . — 28 files already formatted

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