Render README Snippet from Relative Link

Question

Background

I am creating the README.md for my GitHub repo ("MyRepo"), which provides certain VBA functionality. Here I wish to display a code snippet, which the user should paste into their own code.

Since this snippet enables the functionality, it is a crucial element of the project. As such, I maintain it modularly in src/Snippet.bas.

Goal

I am wish to combine the following features for the snippet in my README:

1. The button to copy the snippet with a single click.
2. The scrollable pane, which keeps the README visually uncluttered by the large snippet.
3. The injection of code from an upstream source file.
4. The dynamic injection of the latest code from that file.
5. The relative reference (src/Snippet.bas) to that file, rather than the unwieldy absolute (https://github.com/Greg/MyRepo/tree/HEAD/src/Snippet.bas).
6. The inclusion of the entire file, rather than a fixed section of it (#L14-L22).

Issue

Unfortunately, (1) appears only for code samples written manually within ``` fences; and not for permalinks to the code. As for (2), it appears only for the permalinks; and not for the manually written samples.

While permalinks do achieve (3), they seem anchored to a specific commit, and thus fail at (4). Furthermore, it seems they require the absolute URL, and do not render the relative for (5). Finally, they are anchored rigidly lines (#L14-L22) within the file, and thus do not accommodate (6).

Question

Is there a way to achieve all (or more) of these features in GitHub Flavored Markdown, or in the HTML it permits? Or would this task require sophisticated GitHub Actions?

Alternatively, is there a URL parameter like copy, which automatically copies the linked file to the clipboard?

src/Snippet.bas?copy=1