Seek geek with expert knowledge in WP3 + Apache2 mod_rewrite

I found that I can insert my own PHP code to scrutinize the REQUEST_URI, QUERY_STRING, etc, so I can pull out the parameters needed for my app, and then edit the REQUEST_URI so WordPress is none the wiser, ... and simply displays the proper page. ... then my app code gets invoked, ... plus it has access to my parameters. Solution found.

1. WordPress wants the "Page" name to come last, so I followed your suggestion, but with "app" moved to the end. Same idea as your rule, but rearranged. See .htaccess appended below.

2. The REQUEST_URI is "alpha/beta/app", and the QUERY_STRING "p1=alpha&p2=beta", ...

but the WordPress index.php comes into play and seems to do a REDIRECT (so my app never gets a chance to run)

so that REQUEST_URI becomes "app" and QUERY_STRING is empty. My app code runs, but now it is too late; the parameters are gone.

Any further suggestions?

  # .htaccess
  
  <IfModule mod_rewrite.c>
  RewriteEngine On
  RewriteBase /
  RewriteRule ^index\.php$ - [L]
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteRule ^([^/]+)/([^/]+)/app$ /app/?p1=$1&p2=$2 [QSA,L]
  </IfModule>
  
  # BEGIN WordPress
  <IfModule mod_rewrite.c>
  RewriteEngine On
  RewriteBase /
  RewriteRule ^index\.php$ - [L]
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteRule . /index.php [L]
  </IfModule>
  
  # END WordPress