DL-489
Server-written homes (peer DMs, coordination channels, Linear routing) live in a per-owner system namespace on the channel row: channels.system_namespace (1 DM, 2 coordination, 3 Linear routing) plus channels.namespace_owner_id, unique on (namespace_owner_id, system_namespace, name). No RPC input can set either column, so the reserved-group guards are deleted; the DM resume belt and the Linear wrong-kind refusal stay. ReparentChannel refuses a system channel with INVALID_ARGUMENT. A cross-owner DM keeps the name xdm:<idLo>:<idHi> over the two party account ids, never a handle, with a prefix no same-owner dm: name can produce; a DM name is a resume key, so it carries no reclaimable token. It is homed in the lower owner id’s DM namespace; same-owner DMs keep dm:<lo>:<hi>. A DM convert clears the namespace and frees the name. (Refines DL-294 and DL-296: ‘reserved DM group’ now means the DM system namespace; both stay Active.)
Status: Active (proposed, pending Matt, 2026-10-11)