public Set<Path> getSources() {
        return sources;
    }
Gets the source models, or models that are considered the subject
of the build.

<p>This does not return an exhaustive set of model paths! There are
typically two kinds of models that are added to a build: source
models and discovered models. Discovered models are someone else's
models. Source models are the models owned by the package being built.

@return Returns the source models.
smithy-build/src/main/java/software/amazon/smithy/build/TransformContext.java