Render mermaid diagrams in markdown

[xl0]

What do you want to change?

Render mermaid diagrams in markdown

Why?

Human vision works better withe diagrams.

How? (optional)

Using the grok-mermaid library

[xl0]

Some thoughts from the PR:

• I did not implement this as a built-in extension because we don't have an API that allows extensions to add config variables, and we want t be able to toggle it. I thik this has been brought up before and shut down, but maybe re-consider?

• grok-mermaid always does best-effort rendering, but also outputs an array of warnings. We render best-effort while streaming (to avoid flickering between rendered and failed), but after the messages is complete, we only render if the diagram did not raise warnings, and display the warning if present. The original code blcock is rendered otherwise, same if we don't support the diagram type:

Yes, I display the rendering warning by adding an linine code block, which feels a bit wrong, but is more ergonomic than a notice and does not hide the problem.

To be fair, I have not seen gpt produce a broken diagram unless asked on purpose.

[xl0]

Also, re unicode math. I don't think the renderer should live in pi, because it's either not robust (what I have in https://github.com/xl0/pi-lovely-markdown/blob/master/extensions/lovely-markdown/math.ts right now), or not simple.

I'll put together another library for that.