Re-derive the shared edge pointer and type-check the paint transmute

node-graph/libraries/core-types/src/registry.rs

@@ -124,6 +124,13 @@ impl<N: ?Sized> SharedEdge<N> {
 	pub fn share(&self) -> Self {
 		Self { ptr: self.ptr, own: self.own.clone() }
 	}
+
+	/// Re-derives the cached pointer from the owned payload. An exclusive
+	/// re-borrow of the payload invalidates the pointer taken before it, so
+	/// every mutation through `own` ends here.
+	pub fn rederive(&mut self) {
+		self.ptr = std::ptr::NonNull::from(&*self.own);
+	}
 }
 
 // SAFETY: `ptr` is derived from the owned Arc and never mutated through, so the edge is exactly as
@@ -222,6 +229,7 @@ impl EdgeHandle {
 				let shared = edge.downcast_mut::<SharedEdge<N>>().expect("set_layout hook matches the stored edge type");
 				let node = std::sync::Arc::get_mut(&mut shared.own).expect("layout is installed before the node is shared");
 				Node::<ContextImpl>::set_layout(node, layout);
+				shared.rederive();
 			},
 			ty,
 		}

node-graph/libraries/graphic-types/src/graphic.rs

@@ -378,9 +378,21 @@ fn forced_paint<'a, A: Attribute>(paint: LanePaint<'a>) -> Option<A::Value<'a>>
 		name if name == Stroke::NAME => paint.stroke,
 		_ => None,
 	}?;
+	assert_eq!(
+		std::any::TypeId::of::<A::Value<'static>>(),
+		std::any::TypeId::of::<Option<&'static List<Graphic<'static>>>>(),
+		"attribute `{}` is declared at another value type than this crate's paint form",
+		A::NAME
+	);
+	assert_eq!(
+		size_of::<A::Value<'a>>(),
+		size_of::<Option<&'a List<Graphic<'a>>>>(),
+		"the paint value form must span the marker's value"
+	);
 	// SAFETY: the census admits one value type per attribute name and panics on
-	// a conflict at registration, so a marker named `fill` or `stroke` carries
+	// a conflict at registration, and the asserts above re-check it, so a marker
-	// this crate's `Option<&List<Graphic>>` value form.
+	// named `fill` or `stroke` carries this crate's `Option<&List<Graphic>>`
+	// value form at the same size.
 	Some(unsafe { std::mem::transmute_copy::<Option<&'a List<Graphic>>, A::Value<'a>>(&Some(slot)) })
 }