Syntax grammar guarantees and API

[lmeyerov]

We're thinking through how to do some syntax checking and tool tips during editing of embedded mermaid diagrams, and are wondering:

1. Early detection of errors: If a partial mermaid markdown is written, say the first 10 lines, and a few more to be done, would we expect it to parse successfully? More specifically, if there's a parse failure on that fragment, are we guaranteed there is no additional lines that can be appended after to fix it? I suspect that may be true of any mermaid markdown > 5 lines, but am not sure, and maybe it's mostly true, and only a few known exceptions..

2. We'd love to just call the CLI or a Python API for this kind of check, any guidance on that?

I see the great progress on the CLI and langium ( #4450 ), so curious if any guidance on a future-friendly path here