How to pass a subdomain name using .htaccess to a script without overwriting other parameters?

Question

Domain name market

I make virtual subdomains with

RewriteCond %{HTTP_HOST} ^test\.example\.com$
RewriteCond %{REQUEST_URI} (.*)/$
RewriteRule ^(.*)$ ?sub=test [L]

RewriteCond %{HTTP_HOST} ^demo\.example\.com$
RewriteCond %{REQUEST_URI} (.*)/$
RewriteRule ^(.*)$ ?sub=demo [L]

Not universal, yes...
The problem is that if I pass GET parameters, they are overwritten. Did it like this

RewriteCond %{HTTP_HOST} ^test\.example\.com$
RewriteCond %{REQUEST_URI} (.*)/$
RewriteRule ^(.*)$ ?sub=test&%{QUERY_STRING} [L]

It turns out conditionally such a transformation

http://test.example.com/?q1=1&q2=2
в
http://example.com/?sub=test&?q1=1&q2=2

Not exactly pretty "&?", but it works.
The next step, I wanted to tie this "hack" with the finished CMS, but there was a conflict of rules
example.com/user/admin/, opens the profile, GET data comes

[subaction] => userinfo
[user] => admin

test.example.com/user/admin/, opens the main page, GET data comes in
[test] => test
My edits are before the processing rule

RewriteRule ^user/([^/]*)(/?)+$ index.php?subaction=userinfo&user=$1 [L]

Accordingly, if you swap
test.example.com/user/admin/, opens the profile, GET data arrives

[subaction] => userinfo
[user] => admin

but now my subdomain data is falling off