Editable installs in CI never exercise wheel packaging, which let the
force-include duplication ship broken source installs while tests stayed
green (#308#315#328#332#334). This gate builds the real wheel, fails
on any duplicate archive entry, asserts SKILL.md/guides/scripts ship,
and smoke-installs into a clean venv.
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>