feat: fuel surcharge per lane and cargo type

apps/edr-freight-api/src/contracts/contract-rate-schedule.builder.ts

@@ -193,17 +193,26 @@ export class ContractRateScheduleBuilder {
     return rate.tradeDirection === want;
   }
 
-  /** Fuel row — the lane matters, so it rides along in the charge label. */
+  /**
+   * Fuel row — the lane matters, so it rides along in the charge label.
+   * Per-liter collapses to one flat total (base liters × rate value); the
+   * customer only ever sees the final price.
+   */
   private fuelRow(rate: Rate): RateScheduleRow {
     const origin = rate.originYard?.label ?? rate.originYard?.code ?? '—';
     const destination =
       rate.destinationYard?.label ?? rate.destinationYard?.code ?? '—';
+    const perLiter = rate.rateUnit === 'PER_LITER';
     return {
       route: `Fuel surcharge (${origin} → ${destination})`,
       cargo: this.cargoLabel(rate),
       currency: rate.currency,
-      amount: this.formatAmount(rate.rateValue),
-      unit: this.unitLabel(rate.rateUnit),
+      amount: this.formatAmount(
+        perLiter
+          ? Number(rate.baseLiters ?? 0) * Number(rate.rateValue)
+          : rate.rateValue,
+      ),
+      unit: perLiter ? 'flat' : this.unitLabel(rate.rateUnit),
     };
   }
 

apps/edr-freight-api/src/modules/contracts/contract-pricing.service.ts

@@ -302,15 +302,18 @@ export class ContractPricingService {
             r.cargoTypeId === scope.cargoTypeId,
         );
         if (fuel && Number(fuel.rateValue) > 0) {
-          const base = Number(fuel.baseLiters ?? 0);
+          // Per-liter collapses to one flat total (base liters × rate value) —
+          // the customer only sees the final price, and booking pricing bills
+          // the same flat figure once (see RuleEngineService.fuelCharges).
+          const perLiter = fuel.rateUnit === 'PER_LITER';
+          const total = perLiter
+            ? Number(fuel.baseLiters ?? 0) * Number(fuel.rateValue)
+            : Number(fuel.rateValue);
           lineItems.push({
             code: 'FUEL_SURCHARGE',
-            label:
-              fuel.rateUnit === 'PER_LITER'
-                ? `Fuel surcharge (${scope.cargoType.cargoTypeName}, ${base} liters)`
-                : `Fuel surcharge (${scope.cargoType.cargoTypeName})`,
-            unit: toContractUnit(fuel.rateUnit),
-            unitPrice: convert(Number(fuel.rateValue)),
+            label: `Fuel surcharge (${scope.cargoType.cargoTypeName})`,
+            unit: perLiter ? 'flat' : toContractUnit(fuel.rateUnit),
+            unitPrice: convert(total),
             cargoTypeCode: scope.cargoType.code ?? null,
             conditionalOn: 'has_fuel',
           });

apps/edr-freight-api/src/modules/rule-engine/rule-engine.service.spec.ts

@@ -475,13 +475,16 @@ describe('RuleEngineService — fuel surcharge (per lane + cargo type)', () => {
   const fuelMods = (result: Awaited<ReturnType<RuleEngineService['evaluate']>>) =>
     result.appliedModifiers.filter((m) => m.surchargeCode === 'FUEL_SURCHARGE');
 
-  it('PER_LITER bills base liters × rate value once, regardless of wagons', async () => {
+  it('PER_LITER collapses to one flat total (base liters × rate value), regardless of wagons', async () => {
     const result = await buildService([fuelPerLiter]).evaluate(fuelInput());
     const mods = fuelMods(result);
     expect(mods).toHaveLength(1);
-    expect(mods[0].triggerValue).toBe(100);
+    // Flat: the customer sees only the total, and a frozen contract snapshot
+    // (also stored flat) multiplies it by quantity 1 — never by the liters.
+    expect(mods[0].triggerValue).toBe(1);
+    expect(mods[0].unitPriceUsd).toBe(200);
     expect(mods[0].calculatedAmount).toBe(200);
-    expect(mods[0].billingUnit).toBe('PER_LITER');
+    expect(mods[0].billingUnit).toBe('FLAT');
   });
 
   it('PER_WAGON bills the wagons the cargo occupies', async () => {

apps/edr-freight-api/src/modules/rule-engine/rule-engine.service.ts

@@ -648,9 +648,12 @@ export class RuleEngineService {
   /**
    * Fuel surcharge — fires when the booking's cargo type has hasFuel = true,
    * billed off the FUEL rate matching the booking's lane (trade direction +
-   * origin + destination) and cargo type. PER_LITER bills baseLiters ×
-   * rateValue once per booking; PER_WAGON bills the wagons the cargo occupies.
-   * No matching lane rate simply bills nothing — same leniency as lashing.
+   * origin + destination) and cargo type. PER_LITER collapses to one FLAT
+   * amount (baseLiters × rateValue, once per booking) — the customer only ever
+   * sees the total, and the frozen contract snapshot stores that same flat
+   * figure so the snapshot-override math bills it exactly once. PER_WAGON
+   * bills the wagons the cargo occupies. No matching lane rate simply bills
+   * nothing — same leniency as lashing.
    */
   private fuelCharges(
     input: BookingEvaluationInput,
@@ -673,9 +676,12 @@ export class RuleEngineService {
       0,
       Number(input.bulkWagons ?? 0) || Number(input.totalWagons ?? 0),
     );
-    const billedQty =
-      rate.rateUnit === 'PER_LITER' ? Number(rate.baseLiters ?? 0) : wagons;
-    const amount = billedQty * rateValue;
+    const perLiter = rate.rateUnit === 'PER_LITER';
+    const billedQty = perLiter ? 1 : wagons;
+    const unitPrice = perLiter
+      ? Number(rate.baseLiters ?? 0) * rateValue
+      : rateValue;
+    const amount = billedQty * unitPrice;
     if (!(amount > 0)) return modifiers;
     modifiers.push({
       rateId: rate.id,
@@ -683,8 +689,8 @@ export class RuleEngineService {
       triggerValue: billedQty,
       calculatedAmount: amount,
       currency: rate.currency,
-      unitPriceUsd: rateValue,
-      billingUnit: rate.rateUnit,
+      unitPriceUsd: unitPrice,
+      billingUnit: perLiter ? 'FLAT' : rate.rateUnit,
     });
     return modifiers;
   }