This model splits scale weight change into four components: fat loss, glycogen+water (front-loaded), protein loss (nitrogen-based), and gut content loss (front-loaded).

1) Fat loss: daily_fat_loss = MIN(k * fat_mass, TDEE_base / 3500) * ramp(day)

k = MIN(k_max, k_base * A * F), where A = 1 + ActivityRaw, and F = MIN(1, fat_mass / 25)

2) Glycogen+water (front-loaded): glycogen_g = 6 * lean_kg * TrainingFactor total_glyco_water_lb = glycogen_g * (1 + water_ratio) / 453.6

3) Protein loss (nitrogen-based): N = lean_soft_lb * 0.1; protein_g = N * 6.25 dry_protein_lb = protein_g / 453.6; protein_plus_water_lb = dry_protein_lb * (1 + water_factor) then decays by day

4) Gut content: mass-only front-load over days 1-3.