One block's chrome, dispatching to its slots (ADR-0005 decisions 10, 11, 12, 13).

No branch on a type name, ever

Decision 10's layout and slot_style are how nested groups, lanes and interrupt rails render distinctly without the editor branching on a type name. core.parallel declares layout: :columns, so its lane slots sit side by side and the absence of ordering between them is visible; core.resumable_group declares slot_style: %{"interrupts" => :secondary}, so its interrupt rules render as an attached rail rather than a second body. A host block type with the same structural shape gets the same rendering by declaring the same thing, which is the property that matters. There is no branch anywhere in this module on "core.parallel" or on any other type string, and the operator pre-decision behind ADR-0005 is that there never will be.

icon is a name, never markup. This component takes an icon component as an assign and passes the name to it; a host that ships heroicons renders heroicons, a host that ships nothing gets a neutral glyph. Accepting raw SVG from a callback would be injecting host-authored markup into this package's own render tree - an injection surface, and a guarantee that the icon set fragments across palettes.

Unresolvable blocks (decision 12)

A block whose type does not resolve renders rather than vanishing: its type name, unavailable chrome, a :block finding, its config read-only as canonical JSON (there is no config_schema/1 to drive a form and inventing one would be guessing), and its existing children rendered normally, recursively - the document's slots map preserved every one of them, decoding never having consulted a registry.

It may be selected, moved and deleted. Its config may not be edited. It is never a drop target, because decision 5's first rule needs slots/1 and there is none - Edit.Targets already leaves it out of the droppable set, so nothing here has to re-derive that.

The acceptance property is preservation: open a document containing a block type the host does not have, edit an unrelated part of the tree, save, and the unresolvable block's bytes are unchanged. An editor that quietly dropped it would turn a missing palette entry into silent data loss.

The badge

findings_count covers the whole subtree, so a collapsed node still shows that something inside it needs attention. Decision 11's last sentence is explicit that a finding must never hide inside something folded shut - that is the failure mode that makes tree editors feel unreliable.