A name that a sprite already owns cannot name a property, and a division by zero cannot answer (#63, #64)

#63: a shader Property node named "width" quietly took over the sprite
row of the same name. isSpriteProp lives in PropertySchema now and is
derived from FULL_SCHEMAS.sprite instead of being a second list that
drifts. isValidPropertyName rejects those ten names, and the compiler
reports it at the node as its own problem: "width" is a sprite
property, told apart from "not a word" and from a duplicate.

#64: Divide emitted (a / b) and handed NaN to the driver. It emits
divide(a, b) now, with the guard in the prologue next to straight(),
scalar and per channel: zero divided by zero is zero. That was already
the house rule in the behavior and particle graphs - only the shader
had never been told. Clamp comes along as a shader node for the same
reason: the behavior catalog has had it all along.

src/core/properties/PropertySchema.ts

@@ -306,6 +306,17 @@ export function schemaFor(type: AssetType): PropertySchema {
   return FULL_SCHEMAS[type];
 }
 
+const SPRITE_KEYS = new Set(FULL_SCHEMAS.sprite.map((d) => d.key));
+
+/**
+ * A row every sprite has already: the switch, the transform and the sprite's own. A shader
+ * parameter under one of these names would be a second row on the same bag key, and its uniform
+ * would read the sprite's value instead of the default the Property node declares (#63).
+ */
+export function isSpriteProp(key: string): boolean {
+  return SPRITE_KEYS.has(key);
+}
+
 /**
  * The type schema, for behaviors followed by their declared variables, for sprites by the
  * parameters of the shader asset their bag names – which is why the project is needed.

src/core/properties/shaders.ts

@@ -1,6 +1,6 @@
 import type { Graph, GraphNode } from '../graph/Graph';
 import { type PropertyBag, textOf } from '../model/Properties';
-import { type FlatDef, isValidFieldName } from './PropertySchema';
+import { type FlatDef, isSpriteProp, isValidFieldName } from './PropertySchema';
 
 /** The sprite property naming the shader asset it wears; `''` is no shader and no render pass. */
 export const SHADER_KEY = 'shader';
@@ -27,9 +27,13 @@ export function propertyName(node: GraphNode): string {
   return textOf(node.params[PROPERTY_NAME_PARAM] ?? '');
 }
 
-/** A property's name is a bag key and a uniform, so it has to be an identifier. */
+/**
+ * A property's name is a bag key and a uniform, so it has to be an identifier – and not one of the
+ * rows the sprite brings itself: both rows would share the key and the uniform would read the
+ * sprite's width instead of the declared default (#63). The compiler names which of the two it is.
+ */
 export function isValidPropertyName(name: string): boolean {
-  return isValidFieldName(name);
+  return isValidFieldName(name) && !isSpriteProp(name);
 }
 
 /**