Returns `None` when the node has no `ui::*` attributes at all so callers don't end up with empty entries for unconverted-from-runtime nodes. `input_metadata` is always sized to match `node.inputs.len()` for a strict slot-by-slot rebuild; empty slots use `InputMetadataEntry::default()`.
(node: &crate::Node, network_path: &[RuntimeNodeId], local_id: RuntimeNodeId)
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