Is there a Mustache template key for the request URL path available?

I don't believe there is a global variable which you can use to achieve something approaching {{req.url.path}}.

Could you use JS instead append the image to the footer of each page? Adding something like this to script.js should do the trick:

document.body.innerHTML += 
  `<img src="https://MYCODE.goatcounter.com/count?p=${window.location.path}">`

I came up with a solution.

In all my posts & pages I use the link: metadata e.g.

---
link: /my-link
---

So I realized I was able to use this (if it exists) to include a <noscript>:

<script data-goatcounter="https://MYCODE.goatcounter.com/count" async src="//gc.zgo.at/count.js"></script>
{{#entry.metadata.link}}
<noscript>
  <img src="https://MYCODE.goatcounter.com/count?p={{{entry.metadata.link}}}">
</noscript>
{{/entry.metadata.link}}

It's slightly more complicated on my custom theme, but that's the gist of it.