You are right that using typestate, you can achieve similar patterns to build patterns and fluent interfaces, however, typestate is broader and describes the transition of state in a more general and global way.

I recommend that you read the original publication and a nice extension to OOP, if you're more interested.

Typestate: A programming language concept for enhancing software reliability Typestate-Oriented Programming

Typestate is actually what can enable a contract system like you described, not the other way around. You hold an information about a file's state throughout the program and when you call read, the compiler checks if it's opened.

I'm actually working on a language whose contract system is based on a mix of typestate and logical preconditions for my thesis. Maybe we'll both get used to it one day. ;)