Leading icon + (title over optional subtitle) + trailing control with
4 variants: chevron / value text / switch / badge. Distinct from
add_list_row_v0 (trailing is always icon, no switch/value/badge) and
add_form_field_v0 (label-above-input for forms).
Wires all 9 touchpoints: pen-core builder + index + barrel re-export,
pen-mcp handler + dispatcher case + ext-4 schema, apps/web shim +
Nitro SERVER_BUILDERS, elements.md decision tree #83 + PREFER mapping,
elements-cookbook arg-shape examples, plus shim-server parity case.
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