diff --git a/frontend/src/components/UserListDrawer.vue b/frontend/src/components/UserListDrawer.vue
new file mode 100644
index 0000000..dc548b4
--- /dev/null
+++ b/frontend/src/components/UserListDrawer.vue
@@ -0,0 +1,63 @@
+<script lang="ts" setup>
+import {storeToRefs} from 'pinia'
+import {useUserStore} from '@/stores/user'
+
+defineProps<{
+  modelValue: boolean
+}>()
+
+const userStore = useUserStore()
+const {users} = storeToRefs(userStore)
+
+const emit = defineEmits<{
+  (event: 'update:modelValue', value: boolean): void
+}>()
+
+const getUserInitials = (username: string): string => {
+  if (!username) return '?'
+  return username.trim().slice(0, 2).toUpperCase()
+}
+
+const close = () => emit('update:modelValue', false)
+</script>
+
+<template>
+  <v-navigation-drawer
+    :model-value="modelValue"
+    location="right"
+    temporary
+    width="280"
+    @update:model-value="emit('update:modelValue', $event)"
+  >
+    <v-toolbar density="compact" flat>
+      <v-toolbar-title>Utilisateurs</v-toolbar-title>
+      <v-btn
+        aria-label="Fermer la liste des utilisateurs"
+        icon="mdi-close"
+        size="small"
+        variant="text"
+        @click="close"
+      ></v-btn>
+    </v-toolbar>
+
+    <v-divider></v-divider>
+
+    <v-list v-if="users.length" density="compact">
+      <v-list-item
+        v-for="user in users"
+        :key="user.id"
+        :title="user.username"
+      >
+        <template #prepend>
+          <v-avatar color="primary" size="32">
+            <span class="text-caption font-weight-medium">{{ getUserInitials(user.username) }}</span>
+          </v-avatar>
+        </template>
+      </v-list-item>
+    </v-list>
+
+    <div v-else class="pa-4 text-medium-emphasis text-body-2">
+      Aucun utilisateur à afficher.
+    </div>
+  </v-navigation-drawer>
+</template>
diff --git a/frontend/src/layouts/AppLayout.vue b/frontend/src/layouts/AppLayout.vue
index c7cf0aa..2e86bd4 100644
--- a/frontend/src/layouts/AppLayout.vue
+++ b/frontend/src/layouts/AppLayout.vue
@@ -1,15 +1,24 @@
 <script lang="ts" setup>
 import {storeToRefs} from 'pinia'
 import {useServerStore} from '@/stores/server'
-import {ref} from 'vue'
-import {useRouter} from 'vue-router'
+import {computed, ref, watch} from 'vue'
+import {useRoute, useRouter} from 'vue-router'
 import ContextMenu from "@/components/ContextMenu.vue";
+import UserListDrawer from '@/components/UserListDrawer.vue'
 
 const serverStore = useServerStore()
+const route = useRoute()
 const router = useRouter()
 
 const {servers} = storeToRefs(serverStore)
 
+const showUsersDrawer = ref(false)
+const isServerContext = computed(() => Boolean(route.params.serverId))
+
+watch(isServerContext, (isActive) => {
+  if (!isActive) showUsersDrawer.value = false
+})
+
 const showDialog = ref(false)
 const formData = ref({
   name: '',
@@ -72,13 +81,13 @@ const getServerColor = (str: string): string => {
   const hue = Math.abs(hash) % 360
   return `hsl(${hue}, 60%, 45%)`
 }
+
 </script>
 
 <template>
   <v-app @contextmenu.prevent>
     <!--Top bar-->
     <v-system-bar>
-
       <v-spacer></v-spacer>
 
       <v-icon>mdi-square</v-icon>
@@ -86,6 +95,15 @@ const getServerColor = (str: string): string => {
       <v-icon>mdi-circle</v-icon>
 
       <v-icon>mdi-triangle</v-icon>
+
+      <v-btn
+        v-if="isServerContext"
+        aria-label="Afficher les utilisateurs"
+        icon="mdi-account-group"
+        size="small"
+        variant="text"
+        @click="showUsersDrawer = !showUsersDrawer"
+      ></v-btn>
     </v-system-bar>
 
     <v-navigation-drawer
@@ -127,6 +145,11 @@ const getServerColor = (str: string): string => {
       ></v-btn>
 
     </v-navigation-drawer>
+
+    <UserListDrawer
+      v-model="showUsersDrawer"
+    />
+
     <router-view/>
     <!-- Menu contextuel global -->
     <ContextMenu/>
@@ -184,4 +207,4 @@ const getServerColor = (str: string): string => {
   flex-direction: column;
   gap: 1rem;
 }
-</style>
\ No newline at end of file
+</style>
diff --git a/frontend/src/pages/server/index.vue b/frontend/src/pages/server/index.vue
index 0ae4045..f623182 100644
--- a/frontend/src/pages/server/index.vue
+++ b/frontend/src/pages/server/index.vue
@@ -142,7 +142,11 @@ function onChannelContextMenu(event: MouseEvent, channel: any) {
       width="100%"
     ></v-sheet>
 
-    <v-list v-model:opened="openedCategories" density="compact">
+    <v-list
+      v-model:opened="openedCategories"
+      open-strategy="multiple"
+      density="compact"
+    >
       <template v-for="(item, index) in currentTree" :key="index">
         <!-- Catégorie et ses canaux enfants -->
         <v-list-group v-if="'Category' in item" :value="item.Category[0].id">
diff --git a/src/repositories/server_item_order.rs b/src/repositories/server_item_order.rs
index 7751a48..9ab2406 100644
--- a/src/repositories/server_item_order.rs
+++ b/src/repositories/server_item_order.rs
@@ -1,9 +1,6 @@
 use crate::models::server_item_order;
-use crate::models::server_item_order::OrderedResourceType;
 use crate::repositories::{AnyResult, RepositoryContext};
-use sea_orm::{
-    ActiveModelTrait, ColumnTrait, EntityTrait, QueryFilter, QueryOrder, TransactionTrait,
-};
+use sea_orm::{ColumnTrait, EntityTrait, QueryFilter, QueryOrder};
 use std::sync::Arc;
 use uuid::Uuid;
 
@@ -17,29 +14,9 @@ impl ServerItemOrderRepository {
     pub async fn get_by_server(&self, server_id: Uuid) -> AnyResult<Vec<server_item_order::Model>> {
         Ok(server_item_order::Entity::find()
             .filter(server_item_order::Column::ServerId.eq(server_id))
+            .order_by_asc(server_item_order::Column::ParentCategoryId)
             .order_by_asc(server_item_order::Column::OrderKey)
             .all(&self.context.db)
             .await?)
     }
-
-    /// Réorganise en bloc (reorder) une liste d'éléments dans un serveur ou une catégorie
-    pub async fn update_orders(
-        &self,
-        server_id: Uuid,
-        items: Vec<(Uuid, OrderedResourceType, Option<Uuid>, i64)>, // (resource_id, resource_type, parent_category_id, order_key)
-    ) -> AnyResult<()> {
-        self.context
-            .db
-            .transaction::<_, (), anyhow::Error>(|txn| {
-                Box::pin(async move {
-                    for (resource_id, res_type, parent_cat_id, order_key) in items {
-                        // Logique de mise à jour / upsert des order_key
-                    }
-                    Ok(())
-                })
-            })
-            .await?;
-
-        Ok(())
-    }
 }
diff --git a/src/repositories/server_tree.rs b/src/repositories/server_tree.rs
index 79e68e3..a8db6f5 100644
--- a/src/repositories/server_tree.rs
+++ b/src/repositories/server_tree.rs
@@ -2,7 +2,7 @@ use crate::models::{category, channel, computed_permission, server_item_order};
 use crate::permissions::ChannelPermission;
 use crate::repositories::types::{CategoryWithPermissions, ChannelWithPermissions, ServerTreeData};
 use crate::repositories::{AnyResult, RepositoryContext};
-use sea_orm::{ColumnTrait, EntityTrait, QueryFilter};
+use sea_orm::{ColumnTrait, EntityTrait, QueryFilter, QueryOrder};
 use std::collections::HashMap;
 use std::sync::Arc;
 use uuid::Uuid;
@@ -19,6 +19,8 @@ impl ServerTreeRepository {
                 Ok::<_, anyhow::Error>(
                     server_item_order::Entity::find()
                         .filter(server_item_order::Column::ServerId.eq(server_id))
+                        .order_by_asc(server_item_order::Column::ParentCategoryId)
+                        .order_by_asc(server_item_order::Column::OrderKey)
                         .all(&self.context.db)
                         .await?,
                 )
diff --git a/src/routes/server/mapper.rs b/src/routes/server/mapper.rs
index 26e21d3..470e288 100644
--- a/src/routes/server/mapper.rs
+++ b/src/routes/server/mapper.rs
@@ -67,9 +67,14 @@ pub fn build_server_tree(
     channels: Vec<ChannelWithPermissions>,
     categories: Vec<CategoryWithPermissions>,
 ) -> ServerTreeResponse {
-    let order_map: HashMap<Uuid, i64> = orders
+    let order_map: HashMap<(Option<Uuid>, Uuid), i64> = orders
         .into_iter()
-        .map(|order| (order.resource_id, order.order_key))
+        .map(|order| {
+            (
+                (order.parent_category_id, order.resource_id),
+                order.order_key,
+            )
+        })
         .collect();
 
     let mut category_channels: HashMap<Uuid, Vec<ChannelWithPermissions>> = HashMap::new();
@@ -88,7 +93,12 @@ pub fn build_server_tree(
 
     // Trier les canaux dans chaque catégorie par leur order_key
     for chans in category_channels.values_mut() {
-        chans.sort_by_key(|c| order_map.get(&c.channel.id).copied().unwrap_or(i64::MAX));
+        chans.sort_by_key(|c| {
+            order_map
+                .get(&(c.channel.category_id, c.channel.id))
+                .copied()
+                .unwrap_or(i64::MAX)
+        });
     }
 
     // Préparer les éléments racine (catégories & canaux orphelins) avec leur order_key
@@ -96,7 +106,7 @@ pub fn build_server_tree(
 
     for cat_with_perm in categories {
         let cat_id = cat_with_perm.category.id;
-        let order_key = order_map.get(&cat_id).copied().unwrap_or(i64::MAX);
+        let order_key = order_map.get(&(None, cat_id)).copied().unwrap_or(i64::MAX);
         let chans = category_channels.remove(&cat_id).unwrap_or_default();
 
         let cat_perm_bits = cat_with_perm.permissions.map(|p| p.bits()).unwrap_or(0);
@@ -121,7 +131,7 @@ pub fn build_server_tree(
 
     for chan_with_perm in orphan_channels {
         let order_key = order_map
-            .get(&chan_with_perm.channel.id)
+            .get(&(None, chan_with_perm.channel.id))
             .copied()
             .unwrap_or(i64::MAX);
         let chan_perm_bits = chan_with_perm.permissions.map(|p| p.bits()).unwrap_or(0);
@@ -142,3 +152,92 @@ pub fn build_server_tree(
 
     ServerTreeResponse { items }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::models::{category, channel};
+    use crate::permissions::ChannelPermission;
+    use chrono::Utc;
+
+    fn channel(id: Uuid, category_id: Option<Uuid>, name: &str) -> ChannelWithPermissions {
+        ChannelWithPermissions {
+            channel: channel::Model {
+                id,
+                server_id: Some(Uuid::new_v4()),
+                category_id,
+                channel_type: channel::ChannelType::Text,
+                name: Some(name.to_owned()),
+                created_at: Utc::now(),
+                updated_at: Utc::now(),
+            },
+            permissions: Some(ChannelPermission::empty()),
+        }
+    }
+
+    #[test]
+    fn sorts_channels_by_order_key_within_each_category() {
+        let category_id = Uuid::new_v4();
+        let first_id = Uuid::new_v4();
+        let second_id = Uuid::new_v4();
+
+        let category = CategoryWithPermissions {
+            category: category::Model {
+                id: category_id,
+                server_id: Uuid::new_v4(),
+                name: "Discussion".to_owned(),
+                created_at: Utc::now(),
+                updated_at: Utc::now(),
+            },
+            permissions: Some(ChannelPermission::empty()),
+        };
+
+        let orders = vec![
+            server_item_order::Model {
+                id: Uuid::new_v4(),
+                server_id: category.category.server_id,
+                resource_id: category_id,
+                resource_type: server_item_order::OrderedResourceType::Category,
+                parent_category_id: None,
+                order_key: 1,
+                created_at: Utc::now(),
+                updated_at: Utc::now(),
+            },
+            server_item_order::Model {
+                id: Uuid::new_v4(),
+                server_id: category.category.server_id,
+                resource_id: first_id,
+                resource_type: server_item_order::OrderedResourceType::Channel,
+                parent_category_id: Some(category_id),
+                order_key: 2,
+                created_at: Utc::now(),
+                updated_at: Utc::now(),
+            },
+            server_item_order::Model {
+                id: Uuid::new_v4(),
+                server_id: category.category.server_id,
+                resource_id: second_id,
+                resource_type: server_item_order::OrderedResourceType::Channel,
+                parent_category_id: Some(category_id),
+                order_key: 1,
+                created_at: Utc::now(),
+                updated_at: Utc::now(),
+            },
+        ];
+
+        let response = build_server_tree(
+            orders,
+            vec![
+                channel(first_id, Some(category_id), "second"),
+                channel(second_id, Some(category_id), "first"),
+            ],
+            vec![category],
+        );
+
+        let ServerExplorerItemResponse::Category(_, channels) = &response.items[0] else {
+            panic!("expected a category");
+        };
+        assert_eq!(channels[0].name.as_deref(), Some("first"));
+        assert_eq!(channels[1].name.as_deref(), Some("second"));
+    }
+}
diff --git a/src/services/category.rs b/src/services/category.rs
index 6ca8933..864c9a6 100644
--- a/src/services/category.rs
+++ b/src/services/category.rs
@@ -1,9 +1,7 @@
 use crate::models::category;
-use crate::models::server_item_order::{self, OrderedResourceType};
+use crate::models::server_item_order::OrderedResourceType;
 use crate::services::ServicesContext;
-use sea_orm::{
-    ActiveModelTrait, ColumnTrait, EntityTrait, QueryFilter, QuerySelect, Set, TransactionTrait,
-};
+use sea_orm::{ActiveModelTrait, EntityTrait, Set, TransactionTrait};
 use std::sync::Arc;
 use uuid::Uuid;
 
@@ -24,6 +22,13 @@ impl CategoryService {
     ) -> Result<category::Model, anyhow::Error> {
         let db = &self.service_context.repositories.server.context.db;
         let event_bus = &self.service_context.event_bus;
+        let server_order = self
+            .service_context
+            .services
+            .get()
+            .expect("services initialized")
+            .server_order
+            .clone();
 
         let cat = db
             .transaction::<_, category::Model, anyhow::Error>(|txn| {
@@ -35,25 +40,9 @@ impl CategoryService {
                     };
                     let cat = active.insert(txn).await?;
 
-                    let max_order: Option<i64> = server_item_order::Entity::find()
-                        .filter(server_item_order::Column::ServerId.eq(server_id))
-                        .filter(server_item_order::Column::ParentCategoryId.is_null())
-                        .select_only()
-                        .column_as(server_item_order::Column::OrderKey.max(), "max_key")
-                        .into_tuple::<Option<i64>>()
-                        .one(txn)
-                        .await?
-                        .flatten();
-
-                    let order_item = server_item_order::ActiveModel {
-                        server_id: Set(server_id),
-                        resource_id: Set(cat.id),
-                        resource_type: Set(OrderedResourceType::Category),
-                        parent_category_id: Set(None),
-                        order_key: Set(max_order.unwrap_or(0) + 1),
-                        ..Default::default()
-                    };
-                    order_item.insert(txn).await?;
+                    server_order
+                        .append(txn, server_id, cat.id, OrderedResourceType::Category, None)
+                        .await?;
 
                     Ok(cat)
                 })
@@ -98,10 +87,12 @@ impl CategoryService {
 
         let txn = db.begin().await?;
 
-        server_item_order::Entity::delete_many()
-            .filter(server_item_order::Column::ResourceId.eq(id))
-            .filter(server_item_order::Column::ResourceType.eq(OrderedResourceType::Category))
-            .exec(&txn)
+        self.service_context
+            .services
+            .get()
+            .expect("services initialized")
+            .server_order
+            .remove(&txn, id, OrderedResourceType::Category)
             .await?;
 
         let res = category::Entity::delete_by_id(id).exec(&txn).await?;
diff --git a/src/services/channel.rs b/src/services/channel.rs
index 39c88b4..4661a75 100644
--- a/src/services/channel.rs
+++ b/src/services/channel.rs
@@ -1,10 +1,11 @@
 use crate::domain::dto::channel::{CreateChannelRequest, UpdateChannelRequest};
+use crate::models::server_item_order::OrderedResourceType;
 use crate::models::{channel, role};
 use crate::permissions::PermissionSet;
 use crate::services::ServicesContext;
 use crate::services::permission::PermissionService;
 use sea_orm::{
-    ActiveModelTrait, ColumnTrait, EntityTrait, QueryFilter, QuerySelect, Set, TransactionTrait,
+    ActiveModelTrait, ColumnTrait, EntityTrait, QueryFilter, Set, TransactionTrait,
 };
 use std::sync::Arc;
 use uuid::Uuid;
@@ -25,6 +26,13 @@ impl ChannelService {
     ) -> Result<channel::Model, anyhow::Error> {
         let db = &self.service_context.repositories.server.context.db;
         let event_bus = &self.service_context.event_bus;
+        let server_order = self
+            .service_context
+            .services
+            .get()
+            .expect("services initialized")
+            .server_order
+            .clone();
 
         let channel = db
             .transaction::<_, channel::Model, anyhow::Error>(|txn| {
@@ -42,35 +50,15 @@ impl ChannelService {
 
                     // 2. Si server_id est présent, enregistrement de l'ordre d'affichage
                     if let Some(server_id) = payload.server_id {
-                        let max_order: Option<i64> =
-                            crate::models::server_item_order::Entity::find()
-                                .filter(
-                                    crate::models::server_item_order::Column::ServerId
-                                        .eq(server_id),
-                                )
-                                .select_only()
-                                .column_as(
-                                    crate::models::server_item_order::Column::OrderKey.max(),
-                                    "max_key",
-                                )
-                                .into_tuple::<Option<i64>>()
-                                .one(txn)
-                                .await?
-                                .flatten();
-
-                        let next_order = max_order.unwrap_or(0) + 1;
-
-                        let order_item = crate::models::server_item_order::ActiveModel {
-                            server_id: Set(server_id),
-                            resource_id: Set(channel.id),
-                            resource_type: Set(
-                                crate::models::server_item_order::OrderedResourceType::Channel,
-                            ),
-                            parent_category_id: Set(payload.category_id),
-                            order_key: Set(next_order),
-                            ..Default::default()
-                        };
-                        order_item.insert(txn).await?;
+                        server_order
+                            .append(
+                                txn,
+                                server_id,
+                                channel.id,
+                                OrderedResourceType::Channel,
+                                payload.category_id,
+                            )
+                            .await?;
 
                         // 3. Attribution des permissions par défaut au rôle par défaut
                         if let Some(default_role) = role::Entity::find()
@@ -130,17 +118,19 @@ impl ChannelService {
 
         let channel = active.update(&txn).await?;
 
-        // Update server_item_order parent_category_id or server_id if needed
-        if let Some(server_id) = channel.server_id {
-            crate::models::server_item_order::Entity::update_many()
-                .set(crate::models::server_item_order::ActiveModel {
-                    parent_category_id: Set(channel.category_id),
-                    ..Default::default()
-                })
-                .filter(crate::models::server_item_order::Column::ResourceId.eq(channel.id))
-                .exec(&txn)
-                .await?;
-        }
+        self.service_context
+            .services
+            .get()
+            .expect("services initialized")
+            .server_order
+            .sync(
+                &txn,
+                channel.id,
+                OrderedResourceType::Channel,
+                channel.server_id,
+                channel.category_id,
+            )
+            .await?;
 
         txn.commit().await?;
 
@@ -155,10 +145,12 @@ impl ChannelService {
 
         let txn = db.begin().await?;
 
-        // Delete associated order records
-        crate::models::server_item_order::Entity::delete_many()
-            .filter(crate::models::server_item_order::Column::ResourceId.eq(id))
-            .exec(&txn)
+        self.service_context
+            .services
+            .get()
+            .expect("services initialized")
+            .server_order
+            .remove(&txn, id, OrderedResourceType::Channel)
             .await?;
 
         let res = channel::Entity::delete_by_id(id).exec(&txn).await?;
diff --git a/src/services/server_order.rs b/src/services/server_order.rs
index fcc93de..e74ac43 100644
--- a/src/services/server_order.rs
+++ b/src/services/server_order.rs
@@ -1,5 +1,10 @@
+use crate::models::server_item_order::{self, OrderedResourceType};
 use crate::services::ServicesContext;
+use sea_orm::{
+    ActiveModelTrait, ColumnTrait, DatabaseTransaction, EntityTrait, QueryFilter, QuerySelect, Set,
+};
 use std::sync::Arc;
+use uuid::Uuid;
 
 #[derive(Debug, Clone)]
 pub struct ServerOrderService {
@@ -11,9 +16,303 @@ impl ServerOrderService {
         Self { service_context }
     }
 
+    pub(crate) async fn append(
+        &self,
+        txn: &DatabaseTransaction,
+        server_id: Uuid,
+        resource_id: Uuid,
+        resource_type: OrderedResourceType,
+        parent_category_id: Option<Uuid>,
+    ) -> Result<server_item_order::Model, anyhow::Error> {
+        self.sync(
+            txn,
+            resource_id,
+            resource_type,
+            Some(server_id),
+            parent_category_id,
+        )
+        .await?
+        .ok_or_else(|| anyhow::anyhow!("Unable to create server order"))
+    }
+
+    pub(crate) async fn sync(
+        &self,
+        txn: &DatabaseTransaction,
+        resource_id: Uuid,
+        resource_type: OrderedResourceType,
+        server_id: Option<Uuid>,
+        parent_category_id: Option<Uuid>,
+    ) -> Result<Option<server_item_order::Model>, anyhow::Error> {
+        let existing = server_item_order::Entity::find()
+            .filter(server_item_order::Column::ResourceId.eq(resource_id))
+            .filter(server_item_order::Column::ResourceType.eq(resource_type))
+            .one(txn)
+            .await?;
+
+        let Some(server_id) = server_id else {
+            if let Some(order) = existing {
+                server_item_order::Entity::delete_by_id(order.id)
+                    .exec(txn)
+                    .await?;
+            }
+            return Ok(None);
+        };
+
+        let order_key = match existing.as_ref() {
+            Some(order)
+                if order.server_id == server_id
+                    && order.parent_category_id == parent_category_id =>
+            {
+                order.order_key
+            }
+            _ => {
+                self.next_order_key(txn, server_id, parent_category_id)
+                    .await?
+            }
+        };
+
+        let order = if let Some(order) = existing {
+            let mut active: server_item_order::ActiveModel = order.into();
+            active.server_id = Set(server_id);
+            active.parent_category_id = Set(parent_category_id);
+            active.order_key = Set(order_key);
+            active.update(txn).await?
+        } else {
+            server_item_order::ActiveModel {
+                server_id: Set(server_id),
+                resource_id: Set(resource_id),
+                resource_type: Set(resource_type),
+                parent_category_id: Set(parent_category_id),
+                order_key: Set(order_key),
+                ..Default::default()
+            }
+            .insert(txn)
+            .await?
+        };
+
+        Ok(Some(order))
+    }
+
+    pub(crate) async fn remove(
+        &self,
+        txn: &DatabaseTransaction,
+        resource_id: Uuid,
+        resource_type: OrderedResourceType,
+    ) -> Result<(), anyhow::Error> {
+        server_item_order::Entity::delete_many()
+            .filter(server_item_order::Column::ResourceId.eq(resource_id))
+            .filter(server_item_order::Column::ResourceType.eq(resource_type))
+            .exec(txn)
+            .await?;
+        Ok(())
+    }
+
+    async fn next_order_key(
+        &self,
+        txn: &DatabaseTransaction,
+        server_id: Uuid,
+        parent_category_id: Option<Uuid>,
+    ) -> Result<i64, anyhow::Error> {
+        let mut query = server_item_order::Entity::find()
+            .filter(server_item_order::Column::ServerId.eq(server_id));
+        query = match parent_category_id {
+            Some(category_id) => {
+                query.filter(server_item_order::Column::ParentCategoryId.eq(category_id))
+            }
+            None => query.filter(server_item_order::Column::ParentCategoryId.is_null()),
+        };
+
+        let max_order = query
+            .select_only()
+            .column_as(server_item_order::Column::OrderKey.max(), "max_key")
+            .into_tuple::<Option<i64>>()
+            .one(txn)
+            .await?
+            .flatten()
+            .unwrap_or(0);
+
+        Ok(max_order + 1)
+    }
+
     pub async fn exemple_call_other_service(&self) {
         if let Some(services) = self.service_context.services.get() {
             services.permission_sync.start_listen_event().await;
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::models::{category, server};
+    use crate::repositories::Repositories;
+    use event_bus::EventBus;
+    use migration::{Migrator, MigratorTrait};
+    use sea_orm::{
+        ActiveModelTrait, ColumnTrait, Database, DatabaseConnection, EntityTrait, Set,
+        TransactionTrait,
+    };
+
+    async fn service() -> ServerOrderService {
+        let db = Database::connect("sqlite::memory:").await.unwrap();
+        Migrator::up(&db, None).await.unwrap();
+
+        let context = Arc::new(ServicesContext {
+            repositories: Arc::new(Repositories::new(db)),
+            event_bus: Arc::new(EventBus::new()),
+            services: std::sync::OnceLock::new(),
+        });
+        ServerOrderService::new(context)
+    }
+
+    async fn seed_server(db: &DatabaseConnection, server_id: Uuid) {
+        server::ActiveModel {
+            id: Set(server_id),
+            name: Set("test".to_owned()),
+            is_default: Set(false),
+            ..Default::default()
+        }
+        .insert(db)
+        .await
+        .unwrap();
+    }
+
+    #[tokio::test]
+    async fn sync_uses_scoped_keys_and_preserves_position() {
+        let service = service().await;
+        let db = &service.service_context.repositories.server.context.db;
+        let server_id = Uuid::new_v4();
+        let category_id = Uuid::new_v4();
+        let category_resource_id = Uuid::new_v4();
+        let root_channel_id = Uuid::new_v4();
+        let nested_channel_id = Uuid::new_v4();
+        seed_server(db, server_id).await;
+        category::ActiveModel {
+            id: Set(category_id),
+            server_id: Set(server_id),
+            name: Set("category".to_owned()),
+            ..Default::default()
+        }
+        .insert(db)
+        .await
+        .unwrap();
+
+        let txn = db.begin().await.unwrap();
+        service
+            .append(
+                &txn,
+                server_id,
+                category_resource_id,
+                OrderedResourceType::Category,
+                None,
+            )
+            .await
+            .unwrap();
+        service
+            .append(
+                &txn,
+                server_id,
+                root_channel_id,
+                OrderedResourceType::Channel,
+                None,
+            )
+            .await
+            .unwrap();
+        service
+            .append(
+                &txn,
+                server_id,
+                nested_channel_id,
+                OrderedResourceType::Channel,
+                Some(category_id),
+            )
+            .await
+            .unwrap();
+        txn.commit().await.unwrap();
+
+        let txn = db.begin().await.unwrap();
+        let unchanged = service
+            .sync(
+                &txn,
+                nested_channel_id,
+                OrderedResourceType::Channel,
+                Some(server_id),
+                Some(category_id),
+            )
+            .await
+            .unwrap()
+            .unwrap();
+        assert_eq!(unchanged.order_key, 1);
+
+        let moved = service
+            .sync(
+                &txn,
+                nested_channel_id,
+                OrderedResourceType::Channel,
+                Some(server_id),
+                None,
+            )
+            .await
+            .unwrap()
+            .unwrap();
+        assert_eq!(moved.order_key, 3);
+        txn.commit().await.unwrap();
+    }
+
+    #[tokio::test]
+    async fn sync_none_removes_order_and_rollback_is_atomic() {
+        let service = service().await;
+        let db = &service.service_context.repositories.server.context.db;
+        let server_id = Uuid::new_v4();
+        let resource_id = Uuid::new_v4();
+        seed_server(db, server_id).await;
+
+        let txn = db.begin().await.unwrap();
+        service
+            .append(
+                &txn,
+                server_id,
+                resource_id,
+                OrderedResourceType::Channel,
+                None,
+            )
+            .await
+            .unwrap();
+        txn.rollback().await.unwrap();
+
+        assert!(
+            server_item_order::Entity::find()
+                .filter(server_item_order::Column::ResourceId.eq(resource_id))
+                .one(db)
+                .await
+                .unwrap()
+                .is_none()
+        );
+
+        let txn = db.begin().await.unwrap();
+        service
+            .append(
+                &txn,
+                server_id,
+                resource_id,
+                OrderedResourceType::Channel,
+                None,
+            )
+            .await
+            .unwrap();
+        service
+            .sync(&txn, resource_id, OrderedResourceType::Channel, None, None)
+            .await
+            .unwrap();
+        txn.commit().await.unwrap();
+
+        assert!(
+            server_item_order::Entity::find()
+                .filter(server_item_order::Column::ResourceId.eq(resource_id))
+                .one(db)
+                .await
+                .unwrap()
+                .is_none()
+        );
+    }
+}