Write an attribute under a name the graph supplies

`Named<X>` in parameter position declares where a placeholder's name is
wired, and the macro gives that input constant text; `Attr<Named<X, V>>`
in the return writes under it. The kernel is handed the bare placeholder,
since the name is spent resolving the layout and a folded offset is all
the write needs, so the hot path matches a marker node's exactly.

A name-generic write names its value type through the wired generic,
which only an implementations row resolves, so those nodes emit their
layout meta per row rather than sharing one across rows.

`write_attribute` is the catalog's set half, restoring the identifier
master's documents carry with its input positions. Its name input is a
constant, so those documents resolve without migration, and the reset
marker that stood in for the missing node retires with it.

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

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

@@ -157,7 +157,7 @@ fn flip_entries_tokens(parsed: &ParsedNodeFn, struct_name: &Ident, regular_field
 			quote!(&#layout,)
 		});
 		let element_spec = quote!(gcore::record::ElementSpec::Concrete({ use gcore::record::{ElementWritePickHashed as _, ElementWritePickPlain as _}; (&gcore::record::ElementWritePick::<#row_output>(::core::marker::PhantomData)).element_write() }));
-		let layout_meta = crate::codegen::ir::layout_meta_tokens(&node, element_spec, &core_types);
+		let layout_meta = crate::codegen::ir::layout_meta_tokens(&node, element_spec, &core_types, &assignments);
 		Some(quote! {
 			gcore::registry::RegistryEntry {
 				layout_meta: Some(#layout_meta),
@@ -397,7 +397,7 @@ fn single_row_entries(parsed: &ParsedNodeFn, struct_name: &Ident, regular_fields
 				.collect();
 
 			let carried_meta = || {
-				let meta = ir::layout_meta_tokens(&node, quote!(gcore::record::ElementSpec::Carried), &core_types);
+				let meta = ir::layout_meta_tokens(&node, quote!(gcore::record::ElementSpec::Carried), &core_types, &[]);
 				quote!(Some(#meta))
 			};
 
@@ -432,7 +432,25 @@ fn single_row_entries(parsed: &ParsedNodeFn, struct_name: &Ident, regular_fields
 				ir::NodeKind::RecordIo => {
 					let carrier_arg = (node.inputs.first().is_some_and(|input| input.subject) && ir::materialized_levels(&node, 0) == 0).then(|| quote!(&__layout_0,));
 					let layout_meta_fn = format_ident!("{}_layout_meta", fn_name);
-					(quote!(), quote!(#carrier_arg #(#value_layout_args)*), quote!(Some(self::#layout_meta_fn())))
+					// A name-generic write names its value type through a wired
+					// generic, which only the row resolves, so such a node's
+					// meta is emitted per row instead of shared across them.
+					let named = node.output.shape.attrs.iter().any(|attr| crate::parsing::named_marker(&attr.marker).is_some());
+					let meta = match named {
+						false => quote!(Some(self::#layout_meta_fn())),
+						true => {
+							let element_spec = match &node.output.shape.element {
+								ir::Element::Concrete(element) => {
+									let ty = substitute_ident_types(element, assignments);
+									quote!(gcore::record::ElementSpec::Concrete({ use gcore::record::{ElementWritePickHashed as _, ElementWritePickPlain as _}; (&gcore::record::ElementWritePick::<#ty>(::core::marker::PhantomData)).element_write() }))
+								}
+								_ => quote!(gcore::record::ElementSpec::Carried),
+							};
+							let meta = ir::layout_meta_tokens(&node, element_spec, &core_types, assignments);
+							quote!(Some(#meta))
+						}
+					};
+					(quote!(), quote!(#carrier_arg #(#value_layout_args)*), meta)
 				}
 				ir::NodeKind::Routing => {
 					let source_layouts = base_indices.iter().map(|index| format_ident!("__layout_{index}"));

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

@@ -67,7 +67,10 @@ fn inputs(parsed: &ParsedNodeFn, fields: &[&ParsedField], generics: &[Ident]) ->
 				shape: item_shape(&element, depth, &field.attribute_reads, generics),
 				subject: subject(index, field, carrier_subject, routing.as_ref()),
 				lend: matches!(&field.ty, ParsedFieldType::Regular(RegularParsedField { lend: Some(_), .. })),
-				name_source: crate::parsing::named_source(&element),
+				name_source: match &field.ty {
+					ParsedFieldType::Regular(RegularParsedField { name_source, .. }) => name_source.clone(),
+					ParsedFieldType::Node(_) => None,
+				},
 			}
 		})
 		.collect()
@@ -262,7 +265,10 @@ fn ilist_inner(ty: &Type) -> Option<Type> {
 
 /// Emits the `LayoutMeta` literal from the IR. `element_spec` is supplied by the
 /// caller since it is the one row-dependent facet; the rest folds from the node.
-pub(crate) fn layout_meta_tokens(node: &Node, element_spec: TokenStream2, core_types: &TokenStream2) -> TokenStream2 {
+/// `assignments` binds the row's concrete types to the signature's generics,
+/// which a name-generic write needs: its value type is written as a projection
+/// through the wired generic, so only the row resolves it.
+pub(crate) fn layout_meta_tokens(node: &Node, element_spec: TokenStream2, core_types: &TokenStream2, assignments: &[(Ident, Type)]) -> TokenStream2 {
 	let sources = layout_sources(node).into_iter().map(|index| index as u8);
 	let reads = node
 		.inputs
@@ -275,7 +281,7 @@ pub(crate) fn layout_meta_tokens(node: &Node, element_spec: TokenStream2, core_t
 			quote!(#core_types::record::InputReads { input: #index, reads: ::std::vec![#(#descs),*] })
 		});
 	let writes = field_writes(&node.output.shape.attrs, core_types);
-	let named_writes = named_field_writes(node, core_types);
+	let named_writes = named_field_writes(node, core_types, assignments);
 	let removes = node.output.removes.iter().map(|attr| {
 		let marker = &attr.marker;
 		let level = attr.level;
@@ -369,13 +375,20 @@ fn field_writes(attrs: &[LevelAttr], core_types: &TokenStream2) -> Vec<TokenStre
 
 /// Emits one `NamedWrite` per name-generic write, pairing the template minted
 /// from the concrete value type with the input its placeholder's name sits at.
-fn named_field_writes(node: &Node, core_types: &TokenStream2) -> Vec<TokenStream2> {
+fn named_field_writes(node: &Node, core_types: &TokenStream2, assignments: &[(Ident, Type)]) -> Vec<TokenStream2> {
 	node.output
 		.shape
 		.attrs
 		.iter()
 		.filter_map(|attr| {
 			let (placeholder, value) = crate::parsing::named_marker(&attr.marker)?;
+			let value = qualify_projection(node, &crate::codegen::classify::substitute_ident_types(&value, assignments), assignments);
+			// Only a row resolves a value type written through a generic, so
+			// the row-free meta omits the write rather than naming a type that
+			// is not in scope there.
+			if node.generics.iter().any(|generic| mentions_ident(&value, &generic.ident)) {
+				return None;
+			}
 			let input = name_input(node, &placeholder)? as u8;
 			let level = attr.level;
 			Some(quote!(#core_types::record::NamedWrite::of::<#placeholder, #value>(#input, #level)))
@@ -383,6 +396,51 @@ fn named_field_writes(node: &Node, core_types: &TokenStream2) -> Vec<TokenStream
 		.collect()
 }
 
+/// Rewrites `V::Assoc` into `<Row as Bound>::Assoc` once the row assigns `V`.
+/// A value type reached through an associated type needs the generic's own
+/// bound to name the projection, which only the signature carries.
+fn qualify_projection(node: &Node, ty: &Type, assignments: &[(Ident, Type)]) -> Type {
+	let Type::Path(path) = ty else { return ty.clone() };
+	if path.qself.is_some() || path.path.segments.len() < 2 {
+		return ty.clone();
+	}
+	let base = &path.path.segments[0].ident;
+	let Some(generic) = node.generics.iter().find(|generic| &generic.ident == base) else {
+		return ty.clone();
+	};
+	let Some((_, row)) = assignments.iter().find(|(ident, _)| ident == base) else {
+		return ty.clone();
+	};
+	let mut bounds = generic.bounds.iter().filter_map(|bound| match bound {
+		TypeParamBound::Trait(bound) => Some(&bound.path),
+		_ => None,
+	});
+	let (Some(bound), None) = (bounds.next(), bounds.next()) else {
+		return ty.clone();
+	};
+	let rest = path.path.segments.iter().skip(1);
+	syn::parse_quote!(<#row as #bound>::#(#rest)::*)
+}
+
+/// Whether `ty` names `ident` anywhere, so a type written through a generic
+/// can be told from one already concrete.
+fn mentions_ident(ty: &Type, ident: &Ident) -> bool {
+	struct Search<'a> {
+		ident: &'a Ident,
+		found: bool,
+	}
+
+	impl syn::visit::Visit<'_> for Search<'_> {
+		fn visit_ident(&mut self, found: &Ident) {
+			self.found |= found == self.ident;
+		}
+	}
+
+	let mut search = Search { ident, found: false };
+	syn::visit::Visit::visit_type(&mut search, ty);
+	search.found
+}
+
 /// The input position carrying `placeholder`'s name, which is the parameter
 /// declared at that placeholder.
 pub(crate) fn name_input(node: &Node, placeholder: &Type) -> Option<usize> {
@@ -772,6 +830,35 @@ mod tests {
 		);
 	}
 
+	#[test]
+	fn a_named_write_takes_its_name_from_the_declared_input() {
+		let mut parsed = crate::parsing::parse_node_fn(
+			quote!(category("")),
+			quote!(
+				fn tag<'e, V: WireValue>(ctx: impl Ctx + ExtractArena<'e>, content: f64, name: Named<Name0>, value: V) -> (f64, Attr<'e, Named<Name0, V::Row>>) {
+					(content, Attr(value))
+				}
+			),
+		)
+		.unwrap();
+		parsed.replace_impl_trait_in_input();
+		let node = build(&parsed);
+		let attrs = &node.output.shape.attrs;
+		assert_eq!(attrs.len(), 1, "the write is recorded on the output");
+		let (placeholder, _) = crate::parsing::named_marker(&attrs[0].marker).expect("the marker is name-generic");
+		assert_eq!(name_input(&node, &placeholder), Some(1), "the name comes from the `Named<Name0>` parameter");
+
+		// The row resolves the value type written through the wired generic.
+		let assignments = vec![(syn::parse_quote!(V), syn::parse_quote!(f64))];
+		let emitted = named_field_writes(&node, &quote!(gcore), &assignments);
+		assert_eq!(emitted.len(), 1, "the row carries the named write, got {emitted:?}");
+		assert!(
+			emitted[0].to_string().contains("WireValue"),
+			"the projection is qualified by the generic's bound, got {}",
+			emitted[0]
+		);
+	}
+
 	#[test]
 	fn bridge_record_remove() {
 		assert_bridge(