Compiler: warn when bare state chains are used

We teach users to pass state values into operations.

But state references can go stale (an issue made worse by global state, which I think should be removed, see #17) or not be assigned yet because they are read synchronously.

For example:

get('/some-data')
post('some-data', state.data)

This code will fail because the value of state.data is read synchronously, because the get was completed.

It should be written with some kind of lazy state evaluation, like this:

get('/some-data')
post('some-data, (state) => state.data)

The compiler should be able to detect references to state (literally that global variable reference) and raise a warning when it is used in a naive chain like this.

Start by locating the compiler entry point that analyzes operation chains and references to the global state variable; the issue names no specific file or test. Review the synchronous state example and the proposed lazy callback, then define and test warning behavior for naive state references while preserving valid lazy evaluation.