K3 validates, never defines VINDEX3

K3 — 2.8 trillion parameters, 896 latent-space experts — is the stress test, but the conformance envelope holds five architectures precisely so that no K3-ism becomes the ABI. GPT-OSS, Kimi-Linear, Inkling-Small and a control each contribute a capability nothing else exercises. K3 validates the format; it does not define it.