fix(maintenance-pool): wrap deposit() in dataSource.transaction() to resolve PessimisticLockTransactionRequiredError (#457)

[PINYOPATTANAWASANPORN]

Summary of Changes

Wraps the entire MaintenancePoolService.deposit() in dataSource.transaction() so the SELECT … FOR UPDATE pessimistic lock executes inside an active transaction.

Root Cause (#457)

The #275 fix added setLock('pessimistic_write') to the pool query inside deposit(), but nothing wraps the method in a transaction. TypeORM's SelectQueryBuilder.executeEntitiesAndRawResults guards:

if (this.expressionMap.lockMode === "pessimistic_write" && !queryRunner.isTransactionActive)
  throw new PessimisticLockTransactionRequiredError();

Every POST /maintenance-pool/:id/deposit therefore 500s before reaching any business logic, making the endpoint completely non-functional.

Fix

- async deposit(id, amount, funderAddress): Promise<MaintenancePool> {
-   const pool = await this.poolRepo
-     .createQueryBuilder('pool')
-     .setLock('pessimistic_write')
-     .where('pool.id = :id', { id })
-     .getOne();
+ async deposit(id, amount, funderAddress): Promise<MaintenancePool> {
+   return this.dataSource.transaction(async (manager) => {
+     const pool = await manager
+       .createQueryBuilder(MaintenancePool, 'pool')
+       .setLock('pessimistic_write')
+       .where('pool.id = :id', { id })
+       .getOne();

All subsequent poolRepo.update / poolRepo.increment / findOne calls inside the method are replaced with manager.* equivalents so all operations share the same connection and transaction boundary.

Verification & Testing

5 unit tests added to maintenance-pool.service.spec.ts:

1. wraps deposit() in dataSource.transaction() — dataSource.transaction called once
2. issues SELECT … FOR UPDATE (pessimistic_write) on the manager QueryBuilder — setLock('pessimistic_write') asserted
3. throws NotFoundException when pool is not found inside the transaction
4. throws BadRequestException for a non-ACTIVE pool
5. calls escrowService.fund on first deposit (escrowId is null)

Impact & Compatibility

• Breaking changes: None — deposit() public signature is unchanged.
• DataSource is injected via @InjectDataSource(), already available in the NestJS DI container.

Closes #457

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