watch_muted_must_be_self· reason_code· applies to auth_decision`ak.strand.watch.set` writing `level="muted"` for another actor is rejected — `muted` suppresses mention / moderation / workflow notifications and MUST be opt-in by the target actor themself. `ak.strand.watch.set.others` only authorizes writing `level ∈ {mentions_only, participating, all}` for other actors. See zh/models/strand-and-message.md §8.4.