fix(moveExpenses): clear accounting category when moving to different host

When expenses are moved to an account under a different host, the
AccountingCategoryId is now cleared since accounting categories belong
to specific hosts and would be invalid after the move.

The migration log now also captures the previous AccountingCategoryId
for audit purposes.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: znarf

server/graphql/common/expenses.ts

@@ -4152,6 +4152,12 @@ export const moveExpenses = async (req: express.Request, expenses: Expense[], de
   // -- Move expenses --
   const expenseIds: number[] = uniq(expenses.map(expense => expense.id));
   const recurringExpenseIds: number[] = uniq(expenses.map(expense => expense.RecurringExpenseId).filter(Boolean));
+
+  // Check if moving to a different host - if so, we need to clear accounting categories
+  const isMovingToDifferentHost = expenses.some(
+    e => e.collective.HostCollectiveId !== destinationAccount.HostCollectiveId,
+  );
+
   const result = await sequelize.transaction(async dbTransaction => {
     const associatedTransactionsCount = await models.Transaction.count({
       where: { ExpenseId: expenseIds },
@@ -4162,9 +4168,12 @@ export const moveExpenses = async (req: express.Request, expenses: Expense[], de
       throw new ValidationFailed('Cannot move expenses with associated transactions');
     }
 
-    // Moving associated models
+    // Moving expenses - clear AccountingCategoryId if moving to different host (category belongs to old host)
     const [, updatedExpenses] = await models.Expense.update(
-      { CollectiveId: destinationAccount.id },
+      {
+        CollectiveId: destinationAccount.id,
+        ...(isMovingToDifferentHost && { AccountingCategoryId: null }),
+      },
       {
         transaction: dbTransaction,
         returning: true,
@@ -4231,7 +4240,7 @@ export const moveExpenses = async (req: express.Request, expenses: Expense[], de
       },
     );
 
-    // Record the migration log
+    // Record the migration log (previousExpenseValues includes AccountingCategoryId for audit)
     await models.MigrationLog.create(
       {
         type: MigrationLogType.MOVE_EXPENSES,
@@ -4243,7 +4252,9 @@ export const moveExpenses = async (req: express.Request, expenses: Expense[], de
           comments: updatedComments.map(c => c.id),
           activities: updatedActivities.map(a => a.id),
           destinationAccount: destinationAccount.id,
-          previousExpenseValues: mapValues(keyBy(expenses, 'id'), expense => pick(expense, ['CollectiveId'])),
+          previousExpenseValues: mapValues(keyBy(expenses, 'id'), expense =>
+            pick(expense, ['CollectiveId', 'AccountingCategoryId']),
+          ),
         },
       },
       { transaction: dbTransaction },

test/server/graphql/v2/mutation/RootMutations.test.ts

@@ -7,10 +7,12 @@ import roles from '../../../../../server/constants/roles';
 import { TwoFactorAuthenticationHeader } from '../../../../../server/lib/two-factor-authentication/lib';
 import models from '../../../../../server/models';
 import {
+  fakeAccountingCategory,
   fakeActivity,
   fakeCollective,
   fakeComment,
   fakeExpense,
+  fakeHost,
   fakeMember,
   fakeRecurringExpense,
   fakeTransaction,
@@ -171,7 +173,9 @@ describe('server/graphql/v2/mutation/RootMutations', () => {
         expenses: [testExpense.id],
         recurringExpenses: [],
         destinationAccount: testCollective.id,
-        previousExpenseValues: { [testExpense.id]: { CollectiveId: previousCollective.id } },
+        previousExpenseValues: {
+          [testExpense.id]: { CollectiveId: previousCollective.id, AccountingCategoryId: null },
+        },
         activities: [],
         comments: [],
       });
@@ -263,6 +267,51 @@ describe('server/graphql/v2/mutation/RootMutations', () => {
       await recurringExpense.reload();
       expect(recurringExpense.CollectiveId).to.eq(collective.id);
     });
+
+    it('clears accounting category when moving expense to a different host', async () => {
+      const sourceHost = await fakeHost();
+      const sourceCollective = await fakeCollective({ HostCollectiveId: sourceHost.id });
+      const accountingCategory = await fakeAccountingCategory({ CollectiveId: sourceHost.id, kind: 'EXPENSE' });
+      const destinationHost = await fakeHost();
+      const destinationCollective = await fakeCollective({ HostCollectiveId: destinationHost.id });
+
+      const expense = await fakeExpense({
+        CollectiveId: sourceCollective.id,
+        AccountingCategoryId: accountingCategory.id,
+      });
+
+      const result = await callMoveExpenseMutation(
+        { destinationAccount: { legacyId: destinationCollective.id }, expenses: [{ legacyId: expense.id }] },
+        rootUser,
+      );
+
+      result.errors && console.error(result.errors);
+      expect(result.errors).to.not.exist;
+      await expense.reload();
+      expect(expense.AccountingCategoryId).to.be.null;
+    });
+
+    it('preserves accounting category when moving expense within the same host', async () => {
+      const host = await fakeHost();
+      const sourceCollective = await fakeCollective({ HostCollectiveId: host.id });
+      const destinationCollective = await fakeCollective({ HostCollectiveId: host.id });
+      const accountingCategory = await fakeAccountingCategory({ CollectiveId: host.id, kind: 'EXPENSE' });
+
+      const expense = await fakeExpense({
+        CollectiveId: sourceCollective.id,
+        AccountingCategoryId: accountingCategory.id,
+      });
+
+      const result = await callMoveExpenseMutation(
+        { destinationAccount: { legacyId: destinationCollective.id }, expenses: [{ legacyId: expense.id }] },
+        rootUser,
+      );
+
+      result.errors && console.error(result.errors);
+      expect(result.errors).to.not.exist;
+      await expense.reload();
+      expect(expense.AccountingCategoryId).to.equal(accountingCategory.id);
+    });
   });
 
   describe('editAccountType', () => {