fix issue

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

@@ -132,6 +132,24 @@ export class RatesService {
     );
   }
 
+  /**
+   * True when pricing resolves exactly ONE rate for this shape (base freight,
+   * customs clearance, lashing, empty-container return — all `find()`-based
+   * lookups). For those the unit is not part of the rate's identity: two rows
+   * for the same lane differing only by unit are a duplicate the engine cannot
+   * choose between.
+   *
+   * The additive surcharges are the opposite — the engine bills EVERY matching
+   * rate by its own unit, which is how hazard can be per-container for boxes
+   * and per-ton for bulk at the same time — so their unit stays part of the key.
+   */
+  private resolvesSingleRate(
+    appliesTo: Rate['appliesTo'],
+    trigger: Rate['trigger'],
+  ): boolean {
+    return this.isRouteScoped(appliesTo, trigger) || trigger === 'LASHING';
+  }
+
   /**
    * Which country each end of the leg must sit in, given what the rate is for.
    * The railway only sells three shapes: import lands at the Djibouti ports and
@@ -326,10 +344,17 @@ export class RatesService {
    * Reject a second rate with the same identity pattern (rateType + scope). With
    * effective-date windows gone, two LIVE/DRAFT rates for the same pattern would
    * make pricing ambiguous — so we allow exactly one per pattern.
+   *
+   * The UNIT is not part of that identity. Pricing resolves one rate per lane +
+   * scope and then applies whatever unit it carries; a per-container and a
+   * per-wagon row for the same 20ft lane are two answers to one question, and
+   * the engine silently picked one of them. Changing how a lane is billed means
+   * editing its rate, not adding a second.
    */
   private async assertNoDuplicatePattern(pattern: {
     rateType: string;
-    rateUnit: string;
+    /** Passed only for additive surcharges — see {@link resolvesSingleRate}. */
+    rateUnit?: string;
     containerTypeId: string | null;
     cargoTypeId: string | null;
     tradeDirection: string | null;
@@ -415,7 +440,7 @@ export class RatesService {
 
     await this.assertNoDuplicatePattern({
       rateType,
-      rateUnit,
+      ...(this.resolvesSingleRate(appliesTo, trigger) ? {} : { rateUnit }),
       containerTypeId,
       cargoTypeId,
       tradeDirection,
@@ -600,7 +625,7 @@ export class RatesService {
     // Guard the pattern uniqueness for the new identity, ignoring this row.
     await this.assertNoDuplicatePattern({
       rateType,
-      rateUnit,
+      ...(this.resolvesSingleRate(appliesTo, trigger) ? {} : { rateUnit }),
       containerTypeId: updates.containerTypeId,
       cargoTypeId: updates.cargoTypeId,
       tradeDirection: updates.tradeDirection,