## 27) Error response body shape is inconsistent

backend/app/routers/setup.py

@@ -8,9 +8,10 @@ return ``409 Conflict``.
 from __future__ import annotations
 
 import structlog
-from fastapi import APIRouter, HTTPException, status
+from fastapi import APIRouter, status
 
 from app.dependencies import AppDep, SettingsDep, SettingsServiceContextDep
+from app.exceptions import SetupAlreadyCompleteError
 from app.models.setup import SetupRequest, SetupResponse, SetupStatusResponse, SetupTimezoneResponse
 from app.services import setup_service
 from app.utils.runtime_state import update_app_settings
@@ -59,13 +60,10 @@ async def post_setup(
         :class:`~app.models.setup.SetupResponse` on success.
 
     Raises:
-        HTTPException: 409 if setup has already been completed.
+        SetupAlreadyCompleteError: if setup has already been completed.
     """
     if is_setup_complete_cached(app) or await setup_service.is_setup_complete(settings_ctx.db):
-        raise HTTPException(
-            status_code=status.HTTP_409_CONFLICT,
-            detail="Setup has already been completed.",
-        )
+        raise SetupAlreadyCompleteError()
 
     await setup_service.run_setup(
         settings_ctx.db,