composer: (Maybe bug?) "build" folder is not copied when mirroring

My composer.json:

{
    "name": "graphql-api/graphql-api-for-wp",
    "type": "wordpress-plugin",
    "require": {
        "php": "^7.4|^8.0",
        "graphql-by-pop/graphql-clients-for-wp": "dev-master"
    },
    "repositories": [
        {
            "type": "path",
            "url": "../../../../layers/GraphQLByPoP/packages/graphql-clients-for-wp",
            "options": {
                "symlink": false
            }
        }
    ]
}

Output of composer diagnose:

Checking composer.json: OK
Checking platform settings: OK
Checking git settings: OK
Checking http connectivity to packagist: OK
Checking https connectivity to packagist: OK
Checking github.com oauth access: OK
Checking disk free space: OK
Checking pubkeys: 
Tags Public Key Fingerprint: 57815BA2 7E54DC31 7ECC7CC5 573090D0  87719BA6 8F3BB723 4E5D42D0 84A14642
Dev Public Key Fingerprint: 4AC45767 E5EC2265 2F0C1167 CBBB8A2B  0C708369 153E328C AD90147D AFE50952
OK
Checking composer version: OK
Composer version: 2.0.8
PHP version: 7.4.13
PHP binary path: /usr/local/Cellar/php@7.4/7.4.13_1/bin/php
OpenSSL version: OpenSSL 1.1.1h  22 Sep 2020
cURL version: 7.73.0 libz 1.2.11 ssl (SecureTransport) OpenSSL/1.1.1h
zip: extension present, unzip present

When I run this command:

composer install

It installs my packages. I’m using mirroring since all packages are hosted in a monorepo.

The mirrored package graphql-by-pop/graphql-clients-for-wp (using symlink => false) was successfully copied over, so far everything is OK.

However, the package contains a build folder (this one) that was NOT copied over.

Checking the content of build for the source, produces:

$ ls -l ../../../../layers/GraphQLByPoP/packages/graphql-clients-for-wp/clients/graphiql-with-explorer/build
total 32
-rw-r--r--@ 1 mac  staff  1116 Nov 20 22:38 asset-manifest.json
-rw-r--r--@ 1 mac  staff   420 Nov 20 22:38 index.html
-rw-r--r--@ 1 mac  staff  1253 Nov 20 22:38 precache-manifest.68954ae21e420d7bd929958591027434.js
-rw-r--r--@ 1 mac  staff  1039 Nov 20 22:38 service-worker.js
drwxr-xr-x@ 5 mac  staff   160 Nov 20 22:38 static

Checking the content of build for the mirrored package produces:

$ ls -l vendor/graphql-by-pop/graphql-clients-for-wp/clients/graphiql-with-explorer/build
ls: vendor/graphql-by-pop/graphql-clients-for-wp/clients/graphiql-with-explorer/build: No such file or directory

That build folder contains the output of compiling an application with React, which expects it to be called build, so I can’t rename it.

Is the build folder always being skipped? Is this a bug? Or can I configure this somewhere?