Composer autoloader seems to be not included correctly - php

Question

I'm trying to implement simple library without web server. That means I actually don't have any entry point where I can include autoload.php.
I trying to add bunch of classes, but PhpStorm cannot recognise namespacing and and my classes cannot being auto-imported.
E.g.
I'm trying to import file App/Engines/Contracts/BaseEngine.php which is placed in src/Engines/Contracts/BaseEngine.php via
use App\Engines\Contracts\BaseEngine;
The PhpStorm says Undefined Class
All PhpStorm configuration seems to be correct: I've specified composer.json and checked auto-import in namespace scope.
So, basically the question is: How to deal with composer autoloader in such a library?
Attaching my composer.json code.
{
"name": "mom/task",
"description": "Todo",
"authors": [
{
"name": "Foo Bar",
"email": "foo.mail.com"
}
],
"require": {
"php": "^7.4"
},
"require-dev": {
"phpunit/phpunit": "^8",
"squizlabs/php_codesniffer": "3.*"
},
"autoload": {
"psr-4": {
"App\\": "src/"
}
},
"autoload-dev": {
"psr-4": {
"Tests\\": "tests/"
}
}
}
UPD: attaching BaseEngine code.
<?php
namespace App\Engines\Contracts;
interface BaseEngine
{
/**
* #param int $variable
* #param int $multiplier
* #return mixed
*/
public function compute(int $variable, int $multiplier): int;
}