ReadonlydirtyReadonlykeyReadonlykeyOptional ReadonlyreasonReadonlyrootReadonlyrootFieldPathId (Static IR table index).
Optional ReadonlyrootOptional: mark when the output is TopK-truncated (light/full). Note: truncation does not affect the definition of keyHash/keySize/rootCount (they still refer to full roots).
When dirtyAll=true, a stable reason code must be provided; when dirtyAll=false, it should be omitted.