@@ -81,12 +81,256 @@ pub enum ModerationAuthority {
 /// Returns the matched authority for the audit row, or `Err` with a
 /// client-safe denial message.
 pub async fn authorize_moderation_action(
-    _tenant: &TenantContext,
-    _state: &Arc<AppState>,
-    _actor_pubkey: &[u8],
-    _channel_id: Option<Uuid>,
-    _target: ModerationTarget<'_>,
-    _action: ModerationAction,
+    tenant: &TenantContext,
+    state: &Arc<AppState>,
+    actor_pubkey: &[u8],
+    channel_id: Option<Uuid>,
+    target: ModerationTarget<'_>,
+    action: ModerationAction,
 ) -> anyhow::Result<ModerationAuthority> {
-    todo!("L2 (Mari): relay_members role + channel role lookup, owner>admin guard rails")
+    let community = tenant.community();
+
+    // Community role: `relay_members` stores pubkeys as 64-char hex, fenced to
+    // `community` in the query itself. This is the primary authority — owner and
+    // admin can moderate any channel in their community.
+    let actor_role = state
+        .db
+        .get_relay_member(community, &hex::encode(actor_pubkey))
+        .await?
+        .map(|m| m.role);
+
+    // The target's community role is read only for the admin guard rail — i.e.
+    // an admin actioning a pubkey with ban/timeout — so the owner and
+    // channel-role paths stay at a single query.
+    let target_role = match (actor_role.as_deref(), action, target) {
+        (Some("admin"), ModerationAction::Ban | ModerationAction::Timeout, target) => {
+            match target {
+                ModerationTarget::Pubkey(pk) => state
+                    .db
+                    .get_relay_member(community, &hex::encode(pk))
+                    .await?
+                    .map(|m| m.role),
+                _ => None,
+            }
+        }
+        _ => None,
+    };
+
+    // The channel role is read only when community authority does not apply and
+    // the action is channel-local (DeleteMessage/Kick within `channel_id`).
+    let channel_role = match (actor_role.as_deref(), action, channel_id) {
+        (Some("owner") | Some("admin"), _, _) => None,
+        (_, ModerationAction::DeleteMessage | ModerationAction::Kick, Some(channel_id)) => {
+            state
+                .db
+                .get_member_role(community, channel_id, actor_pubkey)
+                .await?
+        }
+        _ => None,
+    };
+
+    decide_authority(
+        actor_role.as_deref(),
+        target_role.as_deref(),
+        channel_role.as_deref(),
+        action,
+    )
+}
+
+/// Pure authorization decision from resolved roles — the policy, factored out
+/// of the I/O so it is exhaustively unit-testable.
+///
+/// - `actor_role` / `target_role`: community `relay_members` role, if any.
+/// - `channel_role`: the actor's channel role, resolved by the caller only when
+///   community authority does not apply and the action is channel-local.
+fn decide_authority(
+    actor_role: Option<&str>,
+    target_role: Option<&str>,
+    channel_role: Option<&str>,
+    action: ModerationAction,
+) -> anyhow::Result<ModerationAuthority> {
+    match actor_role {
+        // Owner holds every capability, community-wide, with no guard rail.
+        Some("owner") => Ok(ModerationAuthority::CommunityOwner),
+        // Admin holds every capability, but cannot ban/timeout the owner or a
+        // fellow admin — only the owner may action an admin. The guard trips only
+        // on a target *role* of owner/admin: a target with no `relay_members` row
+        // (a drive-by spammer who already left) is bannable. Unban/Untimeout lift
+        // a restriction and are intentionally unguarded — a banned admin can't
+        // self-unban (banned means blocked at the auth seam before any command
+        // runs), so the only reachable case is an admin lifting a fellow admin's
+        // restriction, which is benign, audited, and owner-reversible; guarding it
+        // would instead strand a wrongly-banned admin behind an owner-only unlock.
+        Some("admin") => {
+            if matches!(action, ModerationAction::Ban | ModerationAction::Timeout)
+                && matches!(target_role, Some("owner") | Some("admin"))
+            {
+                anyhow::bail!("an admin cannot ban or time out a community owner or fellow admin");
+            }
+            Ok(ModerationAuthority::CommunityAdmin)
+        }
+        // Not a community owner/admin: channel owner/admin keep channel-local
+        // authority for DeleteMessage/Kick only.
+        _ => match (action, channel_role) {
+            (
+                ModerationAction::DeleteMessage | ModerationAction::Kick,
+                Some("owner") | Some("admin"),
+            ) => Ok(ModerationAuthority::ChannelRole),
+            _ => anyhow::bail!("moderator access required"),
+        },
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    /// Every community-wide action a community owner can take. Channel-local
+    /// actions (DeleteMessage/Kick) are included — the owner holds them too.
+    const ALL_ACTIONS: [ModerationAction; 8] = [
+        ModerationAction::DeleteMessage,
+        ModerationAction::Kick,
+        ModerationAction::Ban,
+        ModerationAction::Unban,
+        ModerationAction::Timeout,
+        ModerationAction::Untimeout,
+        ModerationAction::ResolveReport,
+        ModerationAction::ViewQueue,
+    ];
+
+    fn ok(r: anyhow::Result<ModerationAuthority>) -> ModerationAuthority {
+        r.expect("expected authorization")
+    }
+
+    #[test]
+    fn community_owner_authorized_for_everything() {
+        for action in ALL_ACTIONS {
+            // Even against another owner/admin target: the owner has no guard rail.
+            assert_eq!(
+                ok(decide_authority(Some("owner"), Some("admin"), None, action)),
+                ModerationAuthority::CommunityOwner,
+                "owner must be authorized for {action:?}"
+            );
+        }
+    }
+
+    #[test]
+    fn community_admin_authorized_against_non_privileged_targets() {
+        for action in ALL_ACTIONS {
+            // Target is a plain member (or unknown) — admin holds every capability.
+            assert_eq!(
+                ok(decide_authority(
+                    Some("admin"),
+                    Some("member"),
+                    None,
+                    action
+                )),
+                ModerationAuthority::CommunityAdmin,
+                "admin must be authorized for {action:?} against a member"
+            );
+            assert_eq!(
+                ok(decide_authority(Some("admin"), None, None, action)),
+                ModerationAuthority::CommunityAdmin,
+                "admin must be authorized for {action:?} against a non-member"
+            );
+        }
+    }
+
+    #[test]
+    fn admin_cannot_ban_or_timeout_owner_or_fellow_admin() {
+        for target in ["owner", "admin"] {
+            for action in [ModerationAction::Ban, ModerationAction::Timeout] {
+                assert!(
+                    decide_authority(Some("admin"), Some(target), None, action).is_err(),
+                    "admin must not {action:?} a community {target}"
+                );
+            }
+        }
+    }
+
+    #[test]
+    fn admin_can_ban_or_timeout_a_non_member_target() {
+        // A target with no `relay_members` row (e.g. a drive-by spammer who
+        // already left) must still be bannable — the guard trips on a privileged
+        // *role*, never on a missing row.
+        for action in [ModerationAction::Ban, ModerationAction::Timeout] {
+            assert_eq!(
+                ok(decide_authority(Some("admin"), None, None, action)),
+                ModerationAuthority::CommunityAdmin,
+                "admin must be able to {action:?} a non-member target"
+            );
+            // A plain member target is likewise fair game.
+            assert_eq!(
+                ok(decide_authority(
+                    Some("admin"),
+                    Some("member"),
+                    None,
+                    action
+                )),
+                ModerationAuthority::CommunityAdmin,
+                "admin must be able to {action:?} a plain member"
+            );
+        }
+    }
+
+    #[test]
+    fn admin_guard_rail_is_scoped_to_ban_and_timeout() {
+        // Reversals and non-restriction actions against an admin target are allowed —
+        // the guard rail protects against *applying* a restriction, not lifting one.
+        for action in [
+            ModerationAction::Unban,
+            ModerationAction::Untimeout,
+            ModerationAction::DeleteMessage,
+            ModerationAction::Kick,
+            ModerationAction::ResolveReport,
+            ModerationAction::ViewQueue,
+        ] {
+            assert_eq!(
+                ok(decide_authority(Some("admin"), Some("admin"), None, action)),
+                ModerationAuthority::CommunityAdmin,
+                "admin must be authorized for {action:?} even against an admin target"
+            );
+        }
+    }
+
+    #[test]
+    fn channel_role_covers_only_delete_and_kick() {
+        for role in ["owner", "admin"] {
+            for action in [ModerationAction::DeleteMessage, ModerationAction::Kick] {
+                assert_eq!(
+                    ok(decide_authority(None, None, Some(role), action)),
+                    ModerationAuthority::ChannelRole,
+                    "channel {role} must be authorized for {action:?}"
+                );
+            }
+            // No community authority: channel role does NOT grant community actions.
+            for action in [
+                ModerationAction::Ban,
+                ModerationAction::Timeout,
+                ModerationAction::Unban,
+                ModerationAction::Untimeout,
+                ModerationAction::ResolveReport,
+                ModerationAction::ViewQueue,
+            ] {
+                assert!(
+                    decide_authority(None, None, Some(role), action).is_err(),
+                    "channel {role} must NOT be authorized for community action {action:?}"
+                );
+            }
+        }
+    }
+
+    #[test]
+    fn plain_channel_member_and_stranger_are_denied() {
+        for action in ALL_ACTIONS {
+            assert!(
+                decide_authority(None, None, Some("member"), action).is_err(),
+                "channel member must be denied {action:?}"
+            );
+            assert!(
+                decide_authority(None, None, None, action).is_err(),
+                "user with no role must be denied {action:?}"
+            );
+        }
+    }
 }