Distilled from un33k/python-slugify#180: an argparse option whose dest is
never read — the flag parses, then silently vanishes. slugify defined
--regex-pattern but slugify_params forwarded every namespace field except
args.regex_pattern.

Low-FP by construction (default tier):
- only fires when a sibling dest on the same namespace IS read in-file, so
  consumption is local and the gap is a genuine oversight (not cross-file use);
- a "namespace" is a parse_args() result or a param annotated
  argparse.Namespace — definitions-only files (e.g. httpie's definition.py)
  have neither and stay silent;
- bails on vars()/getattr/setattr/hasattr/__dict__/parse_known_args namespaces
  (dests could be consumed by string);
- skips help/version actions and dynamic/SUPPRESS dests.

Validated: fires exactly once (regex_pattern) on real slugify master; 0
findings across 10 real argparse CLIs (black/flask/pip/aws/pytest/cpython/
youtube-dl/httpie/tenacity/mitmproxy) — httpie went 46->0 after restricting
reads to actual namespace variables. 51 tests pass, ruff clean, self-clean.

Co-Authored-By: claude-flow <ruv@ruv.net>