nx_debt_gate.nx

nx_debt_gate.nx -- R4 GATE: proves debt amortization is bit-exact, detects the minimum-payment trap, and that avalanche pays LESS total interest than snowball (measured, not asserted by faith). EXACT ANCHORS (hand-computed, banker's rounding, 1% monthly = 12% APR): $1,000 @ 12%, pay $2,000 -> 1 month, interest $10.00 (round(1000.00*0.01)=1000c) $1,000 @ 12%, pay $100 -> 11 months, interest $58.98 (5898c) -- full schedule summed by hand $300 @ 0%, pay $100 -> 3 months, interest $0 $10,000 @ 24%, pay $100 -> -1 TRAP (interest $200 > payment $100; never amortizes) MEASURED: A=$10,000@24% min$200 + B=$2,000@6% min$50, budget $500/mo. Avalanche kills the 24% debt first; snowball kills the small $2,000 debt first. Both pay off; avalanche pays less interest. Exits 0 iff ALL pass. license_tier: ORIGINAL