Report input tokens and frame-step output units in response metadata and
record them through the existing usage accounting pipeline. Preserve the
accounting rule and model-specific dimensions as JSON without extending
the gRPC schema for each modality.
Expose animation usage only under metadata.usage, validate counts before
recording, and document the response contract and loaded-model location.
Add coverage for transport, defaults, failures, persistence, and recording
requests once with statistics enabled or disabled.
Assisted-by: Codex:GPT-6
Signed-off-by: Richard Palethorpe <io@richiejp.com>