fix: resolve sync data inconsistency between mobile and web (#55)

Three root causes fixed:

1. API GET /api/sync returned raw entities but mobile client expected
   {changes: [...], sync_token} format — pullChanges() iterated
   data.changes which was undefined, silently skipping all server data.
   Now transforms entities into the SyncPullChange format.

2. Mobile outbox writes used snake_case keys (due_date, list_id, etc.)
   but server processOperation spreads data directly into Drizzle which
   expects camelCase (dueDate, listId). Fixed all outbox writes to use
   camelCase. Also fixed task_tag → taskTag entity type.

3. Missing completedAt in task outbox payloads — completion state was
   lost during sync. Added completedAt to both create and update outbox
   entries, and added Date conversion in server update handler.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/db/repository/lists.ts

@@ -54,7 +54,7 @@ export async function createList(name: string, color?: string, icon?: string) {
     color: color ?? null,
     icon: icon ?? null,
     position: maxPosition + 1,
-    is_inbox: false,
+    isInbox: false,
   }).catch(() => {});
 
   return id;

src/db/repository/outbox.ts

@@ -3,7 +3,7 @@ import { syncOutbox } from '../schema';
 import { randomUUID } from '@/src/lib/uuid';
 import { useSettingsStore } from '@/src/stores/useSettingsStore';
 
-type EntityType = 'task' | 'list' | 'tag' | 'task_tag';
+type EntityType = 'task' | 'list' | 'tag' | 'taskTag';
 type Action = 'create' | 'update' | 'delete';
 
 /**

src/db/repository/tags.ts

@@ -52,7 +52,10 @@ export async function setTagsForTask(taskId: string, tagIds: string[]) {
       tagIds.map((tagId) => ({ taskId, tagId }))
     );
   }
-  writeOutboxEntry('task_tag', taskId, 'update', { task_id: taskId, tag_ids: tagIds }).catch(() => {});
+  // Send individual taskTag create operations (server expects entityId=taskId, data.tagId)
+  for (const tagId of tagIds) {
+    writeOutboxEntry('taskTag', taskId, 'create', { tagId }).catch(() => {});
+  }
 }
 
 export async function addTagToTask(taskId: string, tagId: string) {

src/db/repository/tasks.ts

@@ -176,10 +176,12 @@ export async function createTask(data: {
     id,
     title: data.title,
     notes: data.notes ?? null,
+    completed: false,
+    completedAt: null,
     priority: data.priority ?? 0,
-    due_date: data.dueDate?.toISOString() ?? null,
-    list_id: data.listId,
-    parent_id: data.parentId ?? null,
+    dueDate: data.dueDate?.toISOString() ?? null,
+    listId: data.listId,
+    parentId: data.parentId ?? null,
     recurrence: sanitizedRecurrence,
   }).catch(() => {});
 
@@ -255,10 +257,11 @@ export async function updateTask(
       title: task.title,
       notes: task.notes,
       completed: task.completed,
+      completedAt: task.completedAt ? new Date(task.completedAt).toISOString() : null,
       priority: task.priority,
-      due_date: task.dueDate ? new Date(task.dueDate).toISOString() : null,
-      list_id: task.listId,
-      parent_id: task.parentId,
+      dueDate: task.dueDate ? new Date(task.dueDate).toISOString() : null,
+      listId: task.listId,
+      parentId: task.parentId,
       recurrence: task.recurrence,
     }).catch(() => {});
   }

web/src/app/api/sync/route.ts

@@ -64,12 +64,87 @@ export async function GET(request: NextRequest) {
       .where(inArray(slTaskTags.taskId, taskIds));
   }
 
+  // Transform entities into the changes format expected by the mobile client
+  const changes: {
+    entity_type: string;
+    entity_id: string;
+    action: 'create' | 'update' | 'delete';
+    payload: Record<string, unknown>;
+    updated_at: string;
+  }[] = [];
+
+  for (const l of lists) {
+    changes.push({
+      entity_type: 'list',
+      entity_id: l.id,
+      action: l.deletedAt ? 'delete' : 'update',
+      payload: {
+        name: l.name,
+        color: l.color,
+        icon: l.icon,
+        position: l.position,
+        is_inbox: l.isInbox,
+        created_at: l.createdAt.toISOString(),
+        updated_at: l.updatedAt.toISOString(),
+      },
+      updated_at: l.updatedAt.toISOString(),
+    });
+  }
+
+  for (const t of tasks) {
+    changes.push({
+      entity_type: 'task',
+      entity_id: t.id,
+      action: t.deletedAt ? 'delete' : 'update',
+      payload: {
+        title: t.title,
+        notes: t.notes,
+        completed: t.completed,
+        completed_at: t.completedAt?.toISOString() ?? null,
+        priority: t.priority,
+        due_date: t.dueDate?.toISOString() ?? null,
+        list_id: t.listId,
+        parent_id: t.parentId,
+        position: t.position,
+        recurrence: t.recurrence,
+        created_at: t.createdAt.toISOString(),
+        updated_at: t.updatedAt.toISOString(),
+      },
+      updated_at: t.updatedAt.toISOString(),
+    });
+  }
+
+  for (const tag of tags) {
+    changes.push({
+      entity_type: 'tag',
+      entity_id: tag.id,
+      action: tag.deletedAt ? 'delete' : 'update',
+      payload: {
+        name: tag.name,
+        color: tag.color,
+        created_at: tag.createdAt.toISOString(),
+        updated_at: tag.createdAt.toISOString(),
+      },
+      updated_at: tag.createdAt.toISOString(),
+    });
+  }
+
+  for (const tt of taskTags) {
+    changes.push({
+      entity_type: 'task_tag',
+      entity_id: `${tt.taskId}:${tt.tagId}`,
+      action: 'update',
+      payload: {
+        task_id: tt.taskId,
+        tag_id: tt.tagId,
+      },
+      updated_at: new Date().toISOString(),
+    });
+  }
+
   return NextResponse.json({
-    lists,
-    tasks,
-    tags,
-    taskTags,
-    syncedAt: new Date().toISOString(),
+    changes,
+    sync_token: new Date().toISOString(),
   });
 }
 
@@ -162,9 +237,14 @@ async function processOperation(op: SyncOperation, userId: string) {
       } else if (action === 'update') {
         await verifyOwnership(slTasks, entityId, userId);
         const raw = { ...(data as Record<string, unknown>), updatedAt: now } as Record<string, unknown>;
+        // Remove id from payload to avoid overwriting primary key
+        delete raw.id;
         if (raw.dueDate !== undefined) {
           raw.dueDate = raw.dueDate ? new Date(raw.dueDate as string) : null;
         }
+        if (raw.completedAt !== undefined) {
+          raw.completedAt = raw.completedAt ? new Date(raw.completedAt as string) : null;
+        }
         await db.update(slTasks)
           .set(raw)
           .where(and(eq(slTasks.id, entityId), eq(slTasks.userId, userId)));