{
  "tool_id": "art-335-compute-dti-ratios",
  "note": "golden_hash filled by golden-parity.test.mjs --update. Vector 1: standard within-limits DTI. Vector 2: exceeds manual-UW max, requires AUS. Vector 3: zero-income edge (finite gate).",
  "vectors": [
    {
      "name": "standard_within_limits",
      "description": "$8,000 gross monthly income, $1,800 PITIA, $600 other debts, DU underwriting. Back-end 30% is within the standard-manual 36% band and well under the DU 50% max.",
      "policy_parameters": {
        "gross_monthly_income": 8000,
        "housing_payment_pitia": 1800,
        "other_monthly_debts": 600,
        "underwriting_type": "du"
      },
      "output_payload": {
        "front_end_dti_pct": 22.5,
        "back_end_dti_pct": 30,
        "gross_monthly_income": 8000,
        "housing_payment_pitia": 1800,
        "other_monthly_debts": 600,
        "total_monthly_debt": 2400,
        "dti_tier": "standard_manual",
        "underwriting_type": "du",
        "max_dti_pct": 50,
        "within_max": true,
        "regulatory_basis": "Fannie Mae Selling Guide B3-6-02 (Debt-to-Income Ratios); Freddie Mac Single-Family Seller/Servicer Guide 5401.2 (Debt payment-to-income ratio)",
        "note": "Front-end = housing payment (PITIA) / gross monthly income. Back-end = total monthly debt / gross monthly income. Tier bands are representative GSE manual-underwriting / AUS bands -- confirm against the current Selling Guide / Seller Guide and the specific AUS findings for the loan in question. Not check_agency_eligibility_matrix (art-222), which consumes this ratio as one of several eligibility checks."
      },
      "compliance_flags": [],
      "golden_hash": "d990441e8baf230f60630cec552fb08f86d19afa7271f52f14ba612b02d94f3d"
    },
    {
      "name": "exceeds_manual_max_needs_aus",
      "description": "$6,000 gross monthly income, $2,000 PITIA, $1,000 other debts, manual underwriting selected. Back-end 50% exceeds the manual 45% ceiling; tier shows du_lpa_only meaning an AUS approval (DU/LPA, 50% max) would be required.",
      "policy_parameters": {
        "gross_monthly_income": 6000,
        "housing_payment_pitia": 2000,
        "other_monthly_debts": 1000,
        "underwriting_type": "manual"
      },
      "output_payload": {
        "front_end_dti_pct": 33.33,
        "back_end_dti_pct": 50,
        "gross_monthly_income": 6000,
        "housing_payment_pitia": 2000,
        "other_monthly_debts": 1000,
        "total_monthly_debt": 3000,
        "dti_tier": "du_lpa_only",
        "underwriting_type": "manual",
        "max_dti_pct": 45,
        "within_max": false,
        "regulatory_basis": "Fannie Mae Selling Guide B3-6-02 (Debt-to-Income Ratios); Freddie Mac Single-Family Seller/Servicer Guide 5401.2 (Debt payment-to-income ratio)",
        "note": "Front-end = housing payment (PITIA) / gross monthly income. Back-end = total monthly debt / gross monthly income. Tier bands are representative GSE manual-underwriting / AUS bands -- confirm against the current Selling Guide / Seller Guide and the specific AUS findings for the loan in question. Not check_agency_eligibility_matrix (art-222), which consumes this ratio as one of several eligibility checks."
      },
      "compliance_flags": [
        "DTI_EXCEEDS_MAX"
      ],
      "golden_hash": "9dc09cc4a1ef089debcd67fff81fbd5b306286361a48e7b17210e9b4786c2232"
    },
    {
      "name": "zero_income_edge",
      "description": "Zero gross monthly income. Finite gate must zero the ratios instead of producing Infinity/NaN and flag DTI_ZERO_INCOME.",
      "policy_parameters": {
        "gross_monthly_income": 0,
        "housing_payment_pitia": 1500,
        "other_monthly_debts": 200,
        "underwriting_type": "du"
      },
      "output_payload": {
        "front_end_dti_pct": 0,
        "back_end_dti_pct": 0,
        "gross_monthly_income": 0,
        "housing_payment_pitia": 1500,
        "other_monthly_debts": 200,
        "total_monthly_debt": 1700,
        "dti_tier": "invalid_income",
        "underwriting_type": "du",
        "max_dti_pct": 50,
        "within_max": false,
        "regulatory_basis": "Fannie Mae Selling Guide B3-6-02 (Debt-to-Income Ratios); Freddie Mac Single-Family Seller/Servicer Guide 5401.2 (Debt payment-to-income ratio)",
        "note": "Front-end = housing payment (PITIA) / gross monthly income. Back-end = total monthly debt / gross monthly income. Tier bands are representative GSE manual-underwriting / AUS bands -- confirm against the current Selling Guide / Seller Guide and the specific AUS findings for the loan in question. Not check_agency_eligibility_matrix (art-222), which consumes this ratio as one of several eligibility checks."
      },
      "compliance_flags": [
        "DTI_ZERO_INCOME"
      ],
      "golden_hash": "860cc9ed769654735709908f9051fdc9a4e0e3a319d5242052d81d2b251500bd"
    }
  ]
}