Shouldn't this be handled by ObjectApiEndpoint?

The thing is that method Include#enrichParameters is executed after ObjectApiEndpoint#createBaseParams. So even you set proper values in ObjectApiEndpoint#createBaseParams then they might be overritten in Include#enrichParameters.
I could revert the change you pointed out but then modification of Include#enrichParameters is required from

from

    public Map<String, String> enrichParameters(Map<String, String> baseParams) {
        final Map<String, String> enrichedMap = new HashMap<>(baseParams);
        if (!inclusionFlags.isEmpty()) {
            enrichedMap.put(INCLUDE_PARAM_NAME, join(inclusionFlags));
        }
        return enrichedMap;
    }

to

    public Map<String, String> enrichParameters(Map<String, String> baseParams) {
        final Map<String, String> enrichedMap = new HashMap<>(baseParams);
        if (!inclusionFlags.isEmpty()) {
            String currentIncludeValue = enrichedMap.get(INCLUDE_PARAM_NAME);
            inclusionFlags.add(currentIncludeValue);
            enrichedMap.put(INCLUDE_PARAM_NAME, join(inclusionFlags));
        }
        return enrichedMap;
    }

Do you see other options?

Maybe remove change in ObjectApiEndpoint and that one here and put something like this:

static final Collection<String> DEFAULT_INCLUDE_FLAGS = Arrays.asList("type", "status");

private final List<String> inclusionFlags = new ArrayList<>(DEFAULT_INCLUDE_FLAGS);

That way you should have it regardless of custom being added or not. The question that I have for you though. Are you sure we should add always both type and status? I'm pretty sure it's a status only for memberships, but somehow I don't see it in Kotlin implementation so I don't know anymore

As discussed on a cal I am working on this.

I wonder why populate this uuids list here. Nothing in the step says that it should be done. I'd implemented it by just storing the member data in the state class. Later steps should decide what to do with it

Makes sense. I will change it.

Why not like this?

setChannelMetadataState.pnChannelMetadata = pnChannelMetadata

Good catch. I will modify it.