Formalizes a pattern repeated by hand all session: copy the current
whole-base plan, add a building/recipe, diff simulate() against the
baseline for the true marginal profit and capex (not PRUNplanner's
plan-level ROI, which divides whole-plan profit by only the new capex
and badly overstates once a base exists).
Also flags any workforce tier the addition newly overloads, distinct
from a pre-existing overload it didn't cause - this is what caught the
PP2/pioneer-housing and 2nd-CHP/pioneer-housing surprises by hand
before this tool existed.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
