Adding text between <> characters renders an empty post. (Example in this post)

[sam (Sam Saffron)]

@fzngagan

But in terms of core discourse, how about disallowing submission of a post if its cooked version is less than min post length ?

I am not sure about this, it would not be intuitive to the user. There are going to be edge cases where raw is longer than cooked and it is legitimate.