htaccess - check if original URL in the HTML contained `../` - php

Question

I have a directory tree that looks like:
public_html
_COMMON
INIT.php
project-1
index.php
project-2
index.php
Those two projects use files from _COMMON. First, they load some configuration via the following code in their index.php:
require_once '../_COMMON/INIT.php';
After that, they use common resources via:
<script src="../_COMMON/node_modules/jquery/dist/jquery.min.js"></script>
I have two domains. They are both connected to the same server, meaning they both serve the same files. I want to serve project-1 from:
http://example.com/project-1/
and
http://project1.com/
To do that, I rewrite project1.com URLs to project1.com/project-1/ with the following htaccess:
RewriteCond %{HTTP_HOST} ^(?:www\.)?project1.com$
RewriteCond %{REQUEST_URI} !/project-1
RewriteRule ^(.*)$ /project-1/$1 [L,NC,QSA]
Problem comes here.
The require_once part works because the URL of INIT.php is resolved after the request URL is rewritten, meaning:
User vists http://project1.com/
URL rewritten to http://project1.com/project-1/
Executing http://project1.com/project-1/index.php
http://project1.com/project-1/index.php with ../_COMMON/INIT.php resolved to http://project1.com/_COMMON/INIT.php
However, the script isn't loaded successfully. I guess that's because the URL of jquery.min.js is resolved in the browser, before the URL is rewritten. I guess the following happens:
User vists http://project1.com/
http://project1.com/project-1/index.php is served, but URL is http://project1.com/
Browser sees ../_COMMON/node_modules... and tries to resolve it
Browser initiates a request for http://project1.com/_COMMON/node_modules/jquery/dist/jquery.min.js
URL is rewritten to http://project1.com/project-1/_COMMON/... which doesn't exist
What I've tried
I could just add this:
RewriteCond %{REQUEST_URI} !/_COMMON
to my htaccess and be done.
That's kind of a cheesy solution, though. What If project-1 uses a file from another directory at the root? Adding all those directories in the htaccess seems silly. I don't need to rewrite the URL if it doesn't contain _COMMON, I need to rewrite it if it doesn't go up the directory tree, I.E. if it contains ../. Is there a way to detect that?
Basically, what I want is to not rewrite URLs that begin with ../. I tried:
RewriteCond %{REQUEST_URI} !\.\./
but it doesn't work. I guess it's because that ../ is resolved in the browser, so it's not inside the URL that is actually processed by the htaccess. Is there some other way I could detect whether the original URL contained ../?