> and then to explicitly submit a request to that LLM that explicitly said to read and parse arbitrary issues (including the one created earlier) and then just blindly parse and process and perform whatever those issues said to do, and then blindly make a publicly-visible update to a public repo with the results of those operation(s).

I think you're missing the issue with the latter part.

Prompt injection means that as long as they submit a request to the LLM that reads issues (which may be a request as simple as "summarise the bugs reported today") the all of the remainder can be instructions in the malicious issue.