Subdomains can be seen as a seperate site altogether from the main domain. I would recommend keeping the blog on a directory within the main site.

Hope this helps some.

Depending on what CMS you're using you should be able to add a meta no-index tag sitewide fairly easily. I know with WordPress there's an option in the backend under "Setting", "Reading" Discourage search engines from indexing this site that should allow you to apply a meta no index tag site wide.

If you're not on WordPress you should be able to edit your code and apply a no index sitewide. You might need a tool like FileZilla so you can set up some sort of FTP access and edit your Header file directly.

Cheers

Hey there --

Blocking resources with the robots.txt file prevents search engines from crawling content the no-index tag would be better suited for preventing content from being indexed.

However, previous best practice would dictate blocking access to /wp-includes/ and /wp-content/ directories, etc but that's no longer necessary.

Today, Google will fetch all your styling and JavaScript files so they can render your pages completely. Search engines now try to understand your page's layout and presentation as a key part of how they evaluate quality.

So, yeah this might have some impact on your SEO.

Also, if you're using a plugin to cache content you should want Google to crawl your cache content. And in my experience, Googlebot does a good job of not indexing /wp-content/ sections.

So, for your example page, https://example.com/wp-content/cache/minify/df983.js it shouldn't end up in their index.

Hope this helps some.