In this diagram, the last place that you have my-first-post in context is within the snippet shortcode.
You cannot pass additional context with the .GetPage method, nor can you leverage a page-level .Scratch or .Store because multiple origin pages could be trying to include the same fragment.
I encourage you to think through this and simplify your implementation. Even if you could access the origin page parameters from the final shortcode, the approach seems complicated and fragile.
Thanks @jmooring - that’s exactly what I’m trying to do. Unfortunately I can’t see any other reasonable way of accomplishing the goal - reusing a topic where the content varies in places.