Accept any record wire on an input read only for its attributes

An element generic declared on a reading input, absent from the output
and from every other input, has nowhere to go and nothing to be: the
node reads its declared attributes and never the element. That is an
attr-to-element map, so it accepts any upstream record wire.

The blessing is inferred rather than marked, since the signature already
says it. The two substrate pieces were both in place: the element rides
as the byte-carried token, so the registry takes one generic row instead
of a row per element type, and the reads resolve against the input's own
layout as they always have. Only the passthrough rule stood in the way,
in the three places that enforced it.

A generic the output carries, or one on an input with no reads, is
unchanged and still owes an implementations list.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

node-graph/node-macro/src/codegen.rs

@@ -808,7 +808,9 @@ pub(crate) fn generate_node_impl(crate_ident: &CrateIdent, parsed: &ParsedNodeFn
 	// its generic stays a struct parameter.
 	let record_token = match (kind, &node.output.shape.element) {
 		(crate::codegen::ir::NodeKind::RecordIo, crate::codegen::ir::Element::Generic(ident)) if !gather_carrier => Some(ident.clone()),
-		_ => None,
+		// An opaque reading input's element is byte-carried the same way, even
+		// though the output replaces it rather than carrying it through.
+		_ => crate::codegen::classify::opaque_reading_carrier(parsed),
 	};
 	// The record-io write set, resolved from the output item and carrier input.
 	let write_markers: Vec<&Type> = node.output.shape.attrs.iter().map(|attr| &attr.marker).collect();