feat(api): add equipment domain errors

apps/api/src/equipment/equipment.errors.ts

@@ -0,0 +1,71 @@
+import { HttpException, HttpStatus } from '@nestjs/common';
+
+export type EquipmentErrorCode =
+  | 'CHARACTER_ITEM_NOT_FOUND'
+  | 'ITEM_NOT_OWNED'
+  | 'ITEM_NOT_EQUIPPABLE'
+  | 'ITEM_LEVEL_REQUIREMENT_NOT_MET'
+  | 'INVALID_EQUIPMENT_SLOT'
+  | 'CHARACTER_IN_COMBAT';
+
+export class EquipmentDomainError extends HttpException {
+  constructor(
+    public readonly code: EquipmentErrorCode,
+    status: HttpStatus,
+    message: string,
+  ) {
+    super({ statusCode: status, code, message }, status);
+  }
+}
+
+export function characterItemNotFound(): EquipmentDomainError {
+  return new EquipmentDomainError(
+    'CHARACTER_ITEM_NOT_FOUND',
+    HttpStatus.NOT_FOUND,
+    'This item could not be found.',
+  );
+}
+
+export function itemNotOwned(): EquipmentDomainError {
+  return new EquipmentDomainError(
+    'ITEM_NOT_OWNED',
+    HttpStatus.FORBIDDEN,
+    'This item does not belong to the character.',
+  );
+}
+
+export function itemNotEquippable(): EquipmentDomainError {
+  return new EquipmentDomainError(
+    'ITEM_NOT_EQUIPPABLE',
+    HttpStatus.BAD_REQUEST,
+    'This item cannot be equipped.',
+  );
+}
+
+export function itemLevelRequirementNotMet(): EquipmentDomainError {
+  return new EquipmentDomainError(
+    'ITEM_LEVEL_REQUIREMENT_NOT_MET',
+    HttpStatus.BAD_REQUEST,
+    "The character does not meet this item's level requirement.",
+  );
+}
+
+// Defensive: slot is always derived from the item definition server-side, so
+// this is unreachable in practice (spec §27 still names it explicitly).
+export function invalidEquipmentSlot(): EquipmentDomainError {
+  return new EquipmentDomainError(
+    'INVALID_EQUIPMENT_SLOT',
+    HttpStatus.BAD_REQUEST,
+    'This item does not target a valid equipment slot.',
+  );
+}
+
+export function characterInCombat(): EquipmentDomainError {
+  return new EquipmentDomainError(
+    'CHARACTER_IN_COMBAT',
+    HttpStatus.CONFLICT,
+    'Equipment cannot be changed during an active combat.',
+  );
+}
+
+export { characterNotFound } from '../travel/travel.errors';