I'm struggling to understand why an LLM even needs to be involved in this at all. Can't you write a script that takes the last 10 slack messages and checks the github status for any URLs and adds an emoji? It could be a script or slack bot and it would work far more reliably and cost nothing in LLM calls. IMO it seems far more efficient to have an LLM write a repeatable workflow once than calling an LLM every time.
This reminds of when Adam Wathan admitted that LLMs really helped his workflow due to automating the process for turning SVG's into react components... something that can be handled with a single script rather than calling an LLM every time like you mentioned.
Sometimes people just don't know better.