.htaccess, proper rewriting of directory and file with same name - .htaccess

Question

As of now my website has a few static pages, one of which is /portfolio. Among other things, my htaccess hides the .html extension. I'd like to add a portfolio directory, but I do not want to move my existing portfolio page into the portfolio directory as the default index file. My /portfolio page is one of my Google sitelinks and I am afraid if it is moved or if the url changes in someway, Google will consider it to be a brand new page.
My problem is once I add the /portfolio/ directory, whenever I try to visit the original /portfolio page, a trailing slash is automatically added and it links to the directory itself.
I've tried countless options, one being a rewrite of /portfolio/ to /portfolio, however this creates an infinite loop. I also tried "DirectorySlash Off" but that only removed the trailing slash while being inside the directory, it didn't revert access to the original /portfolio page.
Ultimately, I would like to keep my /portfolio page as-is, linking to pages inside the directory like so /portfolio/example and if either /portfolio or /portfolio/ is accessed it will result in showing the same page which is outside of the directory without Google thinking it is duplicate content.
A similar question exists here:
.htaccess rewriting url to page or directory though this still resulted in an infinite loop for me for some reason, I'm guess it has something to do with the hidden extensions.
Here's my htaccess-
RewriteEngine On
# HTML to PHP
RemoveHandler .html .htm
AddType application/x-httpd-php .htm .html
# Hide extension
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond %{REQUEST_FILENAME}\.html -f
RewriteRule ^(.*)$ $1.html
# Force WWW
RewriteCond %{HTTP_HOST} ^mydomain\.net
RewriteRule ^(.*)$ http://www.mydomain.net/$1 [R=301,L]
# Blog Subdomain
RewriteCond %{HTTP_HOST} ^blog.mydomain.net$
RewriteRule ^(.*)$ http://www.mydomain.net/blog/$1 [R=301,L]
I know it's not a great idea having a directory with the same name as a static page, but I really would rather not alter the existing page and lose the Google sitelink, so a clean and proper way to handle this would be a help.

Answer 1

There are two things going "wrong" here, and two ways to fix it.
The first is that apache "figures out" that there is a directory by the name of "portfolio" before the rewrite conditions are applied. That means that the rewrite conditions are receiving "portfolio/" instead of "portfolio".
Second, the "!-d" rule is specifically avoiding the rewrite that you want to make if there is in fact a directory by that name
Solution 1: Manually re-route requests for the portfolio directory to remove the slash.
# Manually re-route portfolio/ requests to portfolio
RewriteCond %{REQUEST_FILENAME} portfolio/$
RewriteRule ^(.*)/$ $1
# Hide extension
RewriteCond %{REQUEST_FILENAME}\.html -f
RewriteRule ^(.*)$ $1.html
Note the removal of the "!-d" condition.
The downside to this is that you are having to hard-code the "portfolio" edge case directly into the rewrite rules, and will still result in the browser being first redirected to portfolio/
Solution 2: Set DirectorySlash Off and remove directory exists test
# Disable Automatic Directory detection
DirectorySlash Off
# Hide extension
RewriteCond %{REQUEST_FILENAME}\.html -f
RewriteRule ^(.*)$ $1.html
Setting DirectorySlash Off would fix this issue the best, but may break other parts of your site where you actually want the auto DirectorySlash. Best of Luck, and I hope this helps.
Note when testing solution 2, your browser may remember the redirect of "portfolio" to "portfolio/" and perform the redirect before it even sends the request to the server. Be sure to test in a cache-clear, clean environment for best results.