Plan step 23 (containment). The containment showcase gets a dialog with a
long body, whose rules follow its scroll, and one with `separator`, whose
rules always show. The <x-modal> entry in SKILL.md says what `separator`
means now and that every dialog divides a scrolling body by itself.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Qwx5USif3wFFmxtHg5U1g9