diff --git a/backend/alembic.ini b/backend/alembic.ini
index 24512a0..a4d0f3f 100644
--- a/backend/alembic.ini
+++ b/backend/alembic.ini
@@ -1,7 +1,7 @@
 [alembic]
 script_location = migrations
 prepend_sys_path = .
-version_path_separator = os
+path_separator = os
 # Last-resort fallback only. migrations/env.py's _resolve_url() overrides this
 # from the app's own APP_SQLITE_PATH setting (or an `-x sqlalchemy.url=...`
 # argument) whenever either is available — this value is used only if neither is.
diff --git a/backend/app/routers/auth.py b/backend/app/routers/auth.py
index 0cca4da..74be6b9 100644
--- a/backend/app/routers/auth.py
+++ b/backend/app/routers/auth.py
@@ -116,7 +116,7 @@ async def get_context(
     """Return workspace + children for the current user. Used by the dev harness."""
     pd = await pd_repo.get_by_id(current_user.personal_data_uuid)
     if pd is None:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, "No parent profile found")
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, "No parent profile found")
     children = await child_repo.list_by_workspace(pd.workspace_id)
     return _UserContext(
         personal_data_uuid=str(pd.uuid),
diff --git a/backend/app/routers/calendar.py b/backend/app/routers/calendar.py
index 2533df5..6a9bc73 100644
--- a/backend/app/routers/calendar.py
+++ b/backend/app/routers/calendar.py
@@ -31,5 +31,5 @@ async def get_calendar_days(
             workspace_id=workspace_id, start_year=start_year, years=years
         )
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
     return CalendarDaysResponse.from_domain(window)
diff --git a/backend/app/routers/day_overrides.py b/backend/app/routers/day_overrides.py
index de3a9cc..30eae7f 100644
--- a/backend/app/routers/day_overrides.py
+++ b/backend/app/routers/day_overrides.py
@@ -28,7 +28,7 @@ async def upsert_day_override(
             note=payload.note,
         )
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
     return DayOverrideResponse.from_entity(entity)
 
 
diff --git a/backend/app/routers/fetch_data.py b/backend/app/routers/fetch_data.py
index 6986c3e..c42b03b 100644
--- a/backend/app/routers/fetch_data.py
+++ b/backend/app/routers/fetch_data.py
@@ -82,7 +82,7 @@ async def save_manual_entry(
             source=payload.source,
         )
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
     return ParentalLeaveFetchResponse.from_entity(fetch)
 
 
@@ -170,7 +170,7 @@ async def start_fetch(
         children = await child_repo.list_by_workspace(workspace_id)
         if not children:
             raise HTTPException(
-                status.HTTP_422_UNPROCESSABLE_ENTITY,
+                status.HTTP_422_UNPROCESSABLE_CONTENT,
                 "No child in workspace — add one before fetching.",
             )
         child_id = children[0].id
diff --git a/backend/app/routers/leave_wishes.py b/backend/app/routers/leave_wishes.py
index 1179722..81654ef 100644
--- a/backend/app/routers/leave_wishes.py
+++ b/backend/app/routers/leave_wishes.py
@@ -64,7 +64,7 @@ async def create_leave_wish(
             wants_dubbeldag=payload.wants_dubbeldag,
         )
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
     return LeaveWishResponse.from_entity(entity)
 
 
@@ -125,7 +125,7 @@ async def update_leave_wish(
             _clear_target_days="target_days" in fields_set and payload.target_days is None,
         )
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
     except NotFoundError as exc:
         raise HTTPException(status.HTTP_404_NOT_FOUND, str(exc)) from exc
     return LeaveWishResponse.from_entity(entity)
diff --git a/backend/app/routers/plan.py b/backend/app/routers/plan.py
index 7172788..945c0f2 100644
--- a/backend/app/routers/plan.py
+++ b/backend/app/routers/plan.py
@@ -34,7 +34,7 @@ async def propose_plan(
     except NotFoundError as exc:
         raise HTTPException(status.HTTP_404_NOT_FOUND, str(exc)) from exc
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
     return PlanProposalResponse.from_domain(proposal)
 
 
@@ -101,5 +101,5 @@ async def sync_plan(
     except NotFoundError as exc:
         raise HTTPException(status.HTTP_404_NOT_FOUND, str(exc)) from exc
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
     return PlanSyncResponse.from_domain(result)
diff --git a/backend/app/routers/planned_day_exclusions.py b/backend/app/routers/planned_day_exclusions.py
index 67b0e7c..d7d8189 100644
--- a/backend/app/routers/planned_day_exclusions.py
+++ b/backend/app/routers/planned_day_exclusions.py
@@ -39,7 +39,7 @@ async def create_planned_day_exclusion(
             day=payload.date,
         )
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
     return PlannedDayExclusionResponse.from_entity(entity)
 
 
diff --git a/backend/app/routers/planned_days.py b/backend/app/routers/planned_days.py
index 8a8502a..55ff1b7 100644
--- a/backend/app/routers/planned_days.py
+++ b/backend/app/routers/planned_days.py
@@ -30,10 +30,10 @@ def _to_http_error(exc: ValidationError) -> HTTPException:
     """
     if exc.message_key:
         return HTTPException(
-            status.HTTP_422_UNPROCESSABLE_ENTITY,
+            status.HTTP_422_UNPROCESSABLE_CONTENT,
             detail={"message_key": exc.message_key, "data": exc.data},
         )
-    return HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, detail=str(exc))
+    return HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, detail=str(exc))
 
 
 @router.post("", response_model=PlannedLeaveDayResponse, status_code=status.HTTP_201_CREATED)
diff --git a/backend/app/routers/preschool_planning_days.py b/backend/app/routers/preschool_planning_days.py
index 7bbd3f3..7810c5c 100644
--- a/backend/app/routers/preschool_planning_days.py
+++ b/backend/app/routers/preschool_planning_days.py
@@ -32,7 +32,7 @@ async def upsert_planned_days(
     try:
         entity = await service.upsert_planned(child, year, payload.planned_days)
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
     return PreschoolPlanningDaysResponse.from_entity(entity)
 
 
@@ -48,7 +48,7 @@ async def record_taken_days(
     try:
         entity = await service.record_taken(child, year, payload.taken_days)
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
     return PreschoolPlanningDaysResponse.from_entity(entity)
 
 
diff --git a/backend/app/routers/settings.py b/backend/app/routers/settings.py
index db26be7..530e4ae 100644
--- a/backend/app/routers/settings.py
+++ b/backend/app/routers/settings.py
@@ -83,7 +83,7 @@ async def create_child(
         )
         return _child_to_response(child)
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
 
 
 @child_router.get("/{child_id}", response_model=ChildResponse)
@@ -130,7 +130,7 @@ async def update_child(
         )
         return _child_to_response(child)
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
     except NotFoundError as exc:
         raise HTTPException(status.HTTP_404_NOT_FOUND, str(exc)) from exc
 
@@ -164,6 +164,6 @@ async def update_parent_settings(
         )
         return PersonalDataResponse.from_entity(updated)
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
     except NotFoundError as exc:
         raise HTTPException(status.HTTP_404_NOT_FOUND, str(exc)) from exc
diff --git a/backend/app/routers/vacation_days.py b/backend/app/routers/vacation_days.py
index b03abe3..8133fba 100644
--- a/backend/app/routers/vacation_days.py
+++ b/backend/app/routers/vacation_days.py
@@ -30,7 +30,7 @@ async def upsert_vacation_days(
             saved_days_in=payload.saved_days_in,
         )
     except ValidationError as exc:
-        raise HTTPException(status.HTTP_422_UNPROCESSABLE_ENTITY, str(exc)) from exc
+        raise HTTPException(status.HTTP_422_UNPROCESSABLE_CONTENT, str(exc)) from exc
     return VacationDaysResponse.from_entity(entity)
 
 
diff --git a/backend/app/routers/workspace.py b/backend/app/routers/workspace.py
index c09823d..1b2a499 100644
--- a/backend/app/routers/workspace.py
+++ b/backend/app/routers/workspace.py
@@ -48,7 +48,7 @@ def _to_http_error(exc: NotFoundError | ValidationError) -> HTTPException:
     code = (
         status.HTTP_404_NOT_FOUND
         if isinstance(exc, NotFoundError)
-        else status.HTTP_422_UNPROCESSABLE_ENTITY
+        else status.HTTP_422_UNPROCESSABLE_CONTENT
     )
     if exc.message_key:
         return HTTPException(code, detail={"message_key": exc.message_key, "data": exc.data})
@@ -91,7 +91,7 @@ async def update_workspace(
         code = (
             status.HTTP_404_NOT_FOUND
             if isinstance(exc, NotFoundError)
-            else status.HTTP_422_UNPROCESSABLE_ENTITY
+            else status.HTTP_422_UNPROCESSABLE_CONTENT
         )
         raise HTTPException(code, str(exc)) from exc
     return WorkspaceResponse.from_entity(ws)
@@ -220,6 +220,6 @@ async def revoke_invitation(
         code = (
             status.HTTP_404_NOT_FOUND
             if isinstance(exc, NotFoundError)
-            else status.HTTP_422_UNPROCESSABLE_ENTITY
+            else status.HTTP_422_UNPROCESSABLE_CONTENT
         )
         raise HTTPException(code, str(exc)) from exc