JavaScript Type Annotations Proposal Update

Dialog for this update is at https://github.com/tc39/notes/blob/main/meetings/2023-03/mar...

What I would like is a "use: 'typechecked'" at the top of the file indicating that the code has already been checked. This would be accompanied by a new proprosal that defines a standard for what is considered checked (for example checking nullablity in the types) and would allow for browsers to make some optimizations. This could also perhaps reduce the amount of necessary runtime checks such that it would be possible to make it a fully sound typesystem with most of the checks done beforehand.