Validated prototype of the hidden-class object-model change. A vec3-shaped
{:r :g :b} map literal is represented as a cheap Janet tuple [shape vb vg vr]
instead of a struct (~2x cheaper to construct); a lookup on a value the
inference PROVES is the shape reads by bare index with no runtime check.
Result on the ray tracer (direct-link): 12.3s -> 10.7s (~13% faster), with
byte-identical pixel output. The shape value flows transparently through
hit-info/ray/material containers and the colors vector; core-get handles it
(inline check, no fn call) so an unspecialized access is still correct.
Key lessons baked in: the lookup MUST compile to a bare index (a runtime
shape check, even inlined, taxed every field read and made it 2.5-3.4x
SLOWER) — so the inference gained a :shape hint (struct type with keys
exactly {:r :g :b}) that the back end turns into (in m idx). The descriptor
is quoted when embedded (its keys are a parens tuple Janet would otherwise
try to CALL).
All behind JOLT_SHAPE (off by default). Gate green, suite 4718, default-path
bench even. Scoped to the one shape; NOT yet sound in general (assumes every
vec3-shaped value is a shape-rec, true under the flag for the ray tracer) nor
fully transparent (only core-get + the inlined lookup; jolt-call/equality/
print/keys not yet covered). Those are the next steps toward a real feature.
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