Thanks! Looks like our new type system has a few omissions. We’ll try to correct them quickly, for now you can use local typeof = typeof as a workaround (which will silence the warnings by not detecting them), or just live with them for a bit.
Yes - we will support type refinement through predicates. Typed Lua isn’t ready yet but we’re starting to migrate our existing code to share as much as possible with Luau - what you’re seeing is that script analysis is now internally driven by Luau parser and Luau type environment, even though the type system itself hasn’t been enabled yet.