What exacly is transmit! expected to return for merging to work? when I return {:body {:some :map}} , the merge is happening but the target indent is an empty map.

look at the existing implementation. The final merge is based on the return data AND the query component that was used. They must match in shape for things to work right, and the query needs to have the normalizing component on the metadata (still) or it won’t be able to calculate idents.