EpcSimulation is the Simulation Overlay — a narrow all-optional partial
mirror of EpcPropertyData/SapBuildingPart (wall surface first), targeting
building parts by BuildingPartIdentifier (composition, not inheritance).
apply_simulations(baseline, simulations) deep-copies the baseline, folds
overlays in order (later wins on a shared field) via a generic non-None
field write, and returns a throwaway EpcPropertyData for the calculator;
the baseline is never mutated.
Four behaviour tests (hand-built EPD from the 000490 fixture, no PDF):
targeted-write-leaves-others-untouched, empty-overlay no-op, sequential
last-wins, baseline-immutability. pyright strict clean.
Slice 1 of the Modelling stage rebuild (ADR-0016). Closes#1153.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
