tests/Feature/Components/ContainmentStylesheetsTest.php is the
containment twin of InputStylesheetsTest.php and ActionStylesheetsTest.php:
same shape, import and ViewClasses checks, keyed on the "Containment"
block of components.css. Its dataset starts empty and grows by one name
per component commit in this stream (plan step 36).
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9
