Previously if you wanted to reuse the same scalar in different modules you had to redefine it in all of them.
That made sense from the modularity point of view - after all the modules are supposed to be self-sufficient. But scalars are such low-level building blocks that they are usually shared and it made sense to come up with a new pattern.
We discussed and came up with a backward-compatible solution with @jmvtrinidad and @ovidiup13.
Now, starting with version chimp@4.1.2 if you just want to use a scalar in a given module, but do not want to redefine it, use @predefined directive.

For example:

src/global/global.graphql

scalar JSON
scalar Date

src/moduleOne/moduleOne.graphql

type WithJSON {
  id: ID!
  json: JSON!
}
scalar JSON @predefined

src/moduleTwo/moduleTwo.graphql

type WithDate {
  id: ID!
  date: Date!
}
scalar Date @predefined

will result with src/global/scalars/Date.ts and src/global/scalars/JSON.ts files generated and connected to the apollo resolvers object. moduleOne and moduleTwo will NOT generate their versions of scalars but will be using the ones implemented in src/global/scalars/.

Obviously if you extract a given module to a separate micrograph you will need to remove the @predefined keyword and reimplement the scalar. If you are not sure what am I talking about here - don't worry, you probably don't need to. :-)