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.