The GraphInput/GraphOutput cards render through the same build path
as every other node (real graph data, fixed header accents outside
both palettes), GraphOutput as a pure sink with no output ports.
UI-layer protection keeps the pair fixed: the context menu drops the
whole edit section (cut/copy/paste/duplicate/rename/delete) for
them, and delete requests naming an endpoint are narrowed at the
panel — the endpoints and the wires hanging off them always stay,
a request left with nothing is dropped whole. The engine reports the
protected set through AppEngine::protected_graph_nodes (the real
engine resolves Graph::endpoints; the mock demo graph carries its
own marked pair).
Mike-Solar
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