DL-295

The reserved per-owner DM group is server-enforced: CreateChannel refuses any create targeting it (merged not_found) — only the OpenDM path writes there (primary squat defense); the resume/upsert path additionally verify-reconciles DM invariants (kind=DM ∧ mandatory ∧ both parties ⊆ members) as belt.

Status: Active (Matt, 2026-08-30)