8475199609
Replaces the independent log_delta_e/log_edep targets with 2 additive-log-ratio coordinates over the deposit/secondary/post-energy simplex (fractions of pre_E summing to 1), so edep + e_sec + post_E == pre_E holds by construction after decoding (softmax) rather than being learned approximately. Requires e_sec (secondary energy) as a new conditioning input and a steps_to_parquet.py pass to derive it from child track first-step energies.