Positive-time spacetime measurability and finite-L² adapters for the
three fields used by the H_m per-time pairing interface. Quantitative rate
constants remain producer inputs: the Piola-source rate is supplied
directly, while the gradient and d_m rates are read from
HmGradientContract and SourceErrorDContract. The separate adapter
below bounds only the legacy (flux - Kmat) : ∇Gbar contraction.
The five AEStronglyMeasurable fields consumed by
hm_per_time_pairing_data_of_joint_fields_and_spacetime_eLpNorm, deduced from
the actual joint-continuity construction.
HmGradientContract gives the spacetime vector L² bound consumed by
the pairing assembler. The closed-time extension supplies the integrability
needed to interpret its real-valued energy as an actual square integral.
The SourceErrorDContract time-slice Euclidean rate supplies the matching
spacetime eLpNorm bound for d_m, with the same source-rate constant.