SpectrumOutputSpec.outputPrimaries property

Desired output colourimetry. The pipeline auto-injects whatever conversions are needed (TransferFunction, GamutMap, range conversion) to reach these from the kernel-natural upstream — for example, a toneMap chain followed by outputTransfer: "bt709" will deliver an SDR BT.709-encoded stream rather than linear-light. Omit any field to mirror the kernel’s natural output for that aspect.

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