The solution is to create an action that acts as an endpoint for reading data from the other application. Our security model assumes that each application owns its data. If it needs to share data with another application, it can use custom events or expose an endpoint.
Similar to that question, we recommend practicing caution when considering a solution to share data between applications as it can give users access to data that they are not supposed to be able to see.
In regards to the file lib, it is tied to one namespace at the moment and doesn't allow cross-namespace access.