nx_purchase.nx

nx_purchase.nx -- R4 of THE NISHI SITUATION-MANAGEMENT arc: the PURCHASE-DECISION / OPPORTUNITY-COST engine that powers the Nishi browser's "before you buy" check (operator: "showing what you have vs what it will cost and help with the opportunity costs"). Grounded in REAL economics, not invented (corpus: knowledge/fetched/spend_*.raw -- opportunity cost, time value of money, hyperbolic discounting/present bias [why showing the future cost works], impulse/nudge/cooling-off). THE KEY INSIGHT (opportunity cost, exact): if you carry high-interest debt, a $X purchase is not $X -- it is $X you did NOT put toward that debt, so it costs you $X PLUS the interest you forgo saving. The engine computes that EXACTLY by two nx_debt amortization runs (R4-gated): interest(balance) minus interest(balance - X). It also shows "what you have" (affordability from your available cash) and the concrete reframes that counter present bias: hours-of-your-life and %-of-your-goal. Composes nx_money + nx_debt + nx_adhd. No floats, no hardware writes, ADVISORY only (autonomy). license_tier: ORIGINAL