The hydrator round-trips _subjectSubscriptions by reflection.
Stored as a plain JSON object (subjectId → {followed,
mutedSurfaces}); structured-value persistence per the
ContactsMixin._contacts precedent. Default {} hydrates legacy
avatar docs (no field) cleanly.
The hydrator round-trips
_subjectSubscriptionsby reflection. Stored as a plain JSON object (subjectId → {followed, mutedSurfaces}); structured-value persistence per theContactsMixin._contactsprecedent. Default{}hydrates legacy avatar docs (no field) cleanly.