PropertyValue was number | string | boolean | list. A struct joins it, which
costs two things the typechecker found rather than I did.
An object on a data edge used to mean a live entity, so asEntity would have
taken a struct for one and asString would have read .name off it. EntityHandle
now carries a symbol brand – a symbol so no field name can impersonate it, and
it never serializes, which suits a thing that exists only while the game runs.
It is built in exactly one place.
String(value) would have written a struct as [object Object] at 39 call sites.
They go through textOf(), which is identical for primitives.
normalizeGraph dropped everything but primitives from node params, so the List
node lost its value on every save ([3,1,4] round-tripped to undefined).
Variables were spared: they have a schema, params have none.