Authoring Markdown externally and getting even 'prettier' output in Slack with `md2slack`

You know what's a little bit sad to think to yourself? Wow, I'm a little bit jealous of how nice that person's Slack message looks And yet, that something I thought to myself last week 😅 I was looking at a colleague's message - which was posted to Slack via Claude - and it had the regular sort of rendered-Markdown that you'd expect from Slack, but inline in the message it had a pretty-rendered table, and a syntax-highlighted code snippet, followed by other bits of text. (Aside: I'm not really a fan of people using AI to post to Slack, because it infers that a) the human may not be involved in the loop and b) does that mean all our private conversations are now being ingested by the AI provider?) This wasn't a "normal" message that could be posted normally, especially as it included multiple types of content all rendered nicely. After doing some digging, it looks like it was created using the Slack Block Kit, which is much more powerful than the interface you get through Slack's…