feat: implement 20ft container weight-pairing validation

- Added ContainerValidationService to handle 20ft weight-pairing logic.
- Introduced validate20ftWeightPairing utility function to check weight differences.
- Updated BookingPricingService to include overweight line details and pairing errors in price response.
- Enhanced BookingTransitionService to reject submissions with unpairable 20ft containers.
- Created ShipmentValidation interface for pre-submit validation of container contracts.
- Integrated shipment validation into the contract booking process, providing warnings for overweight containers and hard blocks for pairing errors.
- Updated front-end components to display validation results and prevent submission when errors are present.

apps/edr-freight-api/src/modules/bookings/container-validation.service.ts

@@ -0,0 +1,76 @@
+import { Injectable } from '@nestjs/common';
+import { InjectDataSource } from '@nestjs/typeorm';
+import { DataSource, In } from 'typeorm';
+
+import { TrainSchedulingGlobalRules } from '../train-scheduling/entities/train-scheduling-global-rules.entity';
+import { Booking } from './entities/booking.entity';
+import { BookingContainerUnit } from './entities/booking-container-unit.entity';
+import {
+  Container20ftUnit,
+  PairingViolation,
+  validate20ftWeightPairing,
+} from './container-pairing.util';
+
+/** Default 20ft pair weight-difference cap when no global rules row exists (matches the entity default). */
+const DEFAULT_MAX_20FT_PAIR_DIFF_TONS = 10;
+
+/**
+ * Booking-time container validations that need the customer-entered per-unit
+ * weights (`BookingContainerUnit`): the 20ft weight-pairing rule. Kept out of the
+ * rule engine (which works on line totals) because pairing is per physical unit.
+ */
+@Injectable()
+export class ContainerValidationService {
+  constructor(@InjectDataSource() private readonly dataSource: DataSource) {}
+
+  private async maxPairDiffTons(): Promise<number> {
+    const row = await this.dataSource
+      .getRepository(TrainSchedulingGlobalRules)
+      .find({ order: { createdAt: 'ASC' }, take: 1 })
+      .then((rows) => rows[0] ?? null)
+      .catch(() => null);
+    const v = row?.max20ftPairWeightDiffTons;
+    const n = v == null ? NaN : Number(v);
+    return Number.isFinite(n) ? n : DEFAULT_MAX_20FT_PAIR_DIFF_TONS;
+  }
+
+  /** Load every 20ft container UNIT weight for a booking (customer-entered VGM). */
+  private async load20ftUnits(booking: Booking): Promise<Container20ftUnit[]> {
+    const lines = (booking.bookingContainers ?? []).filter(
+      (bc) => (bc.containerSize ?? '').includes('20'),
+    );
+    if (!lines.length) return [];
+
+    const units = await this.dataSource
+      .getRepository(BookingContainerUnit)
+      .find({
+        where: { bookingContainerId: In(lines.map((l) => l.id)) },
+        order: { sortOrder: 'ASC' },
+      });
+
+    return units.map((u) => ({
+      label: u.containerNumber || u.id.slice(0, 8),
+      grossWeightTons: Number(u.vgmTons ?? 0),
+    }));
+  }
+
+  /**
+   * Validate the 20ft weight-pairing rule for a booking. Returns one message per
+   * pair whose weight difference exceeds the cap; empty when all 20ft can be
+   * balanced onto wagons (or there is nothing to pair). A lone odd 20ft is fine —
+   * it flows to consolidation. Callers hard-block a non-empty result.
+   */
+  async validate20ftPairing(booking: Booking): Promise<PairingViolation[]> {
+    // Only bookings whose 20ft lines actually carry per-unit weights can be
+    // checked; contract-drawdown bookings do (units are required there).
+    const containerLines = booking.bookingContainers ?? [];
+    const has20ft = containerLines.some((bc) => (bc.containerSize ?? '').includes('20'));
+    if (!has20ft) return [];
+
+    const units = await this.load20ftUnits(booking);
+    if (units.length < 2) return [];
+
+    const maxDiff = await this.maxPairDiffTons();
+    return validate20ftWeightPairing(units, maxDiff);
+  }
+}