Three sizes, one anatomy
White panel · cobalt-200 stroke · mono-uppercase chip header · icon+label rows. Don't add an outer shadow, don't fill the panel, don't make it bigger than the prisms it sits next to.
Default, input side. Reads as "things that flow into the platform."
.sidebox · 220 × autoOutput side, what the platform produces, where it lands.
.sidebox · 220 × autoCompact, when the diagram is dense and you need a tight column. Trailing "+ N more" instead of a long list.
.sidebox--compactWhere the rectangle pulls its weight
The shape difference between hex and rectangle is doing real work. Don't muddy it.
Do
Use a side-box for anything not built by Conduction: data sources, identity providers, downstream APIs, third-party SaaS, your customers, citizens, regulators. The rectangle says "external."
Don't
Don't put a Conduction app inside a side-box because the diagram got crowded. If the cluster won't fit, swap the radial cluster for the horizontal pipeline-flow variant.
Do
Cap rows at 5. If you need more, use the compact variant with a "+ N more" footer, or split into two side-boxes labeled by sub-category.
Don't
Don't switch the side-box stroke to KNVB orange to "highlight" it. Side-boxes are intentionally quieter than the prisms, that's the whole hierarchy.