refactor: split calendar source setup orchestration

src/govoplan_calendar/backend/router.py

@@ -99,6 +99,15 @@ from govoplan_core.db.session import get_session
 router = APIRouter(prefix="/calendar", tags=["calendar"])
 
 
+def _caldav_discovery_http_error(
+    exc: CalendarError | CalDAVError,
+) -> HTTPException:
+    return HTTPException(
+        status_code=status.HTTP_422_UNPROCESSABLE_CONTENT,
+        detail=str(exc),
+    )
+
+
 def _require_scope(principal: ApiPrincipal, scope: str) -> None:
     if not has_scope(principal, scope):
         raise HTTPException(status_code=status.HTTP_403_FORBIDDEN, detail=f"Missing scope: {scope}")
@@ -492,7 +501,7 @@ def api_discover_caldav_calendars(
         calendars = discover_caldav_calendars(session, tenant_id=principal.tenant_id, payload=payload)
         return CalendarCalDavDiscoveryResponse(calendars=calendars)
     except (CalendarError, CalDAVError) as exc:
-        raise HTTPException(status_code=status.HTTP_422_UNPROCESSABLE_CONTENT, detail=str(exc)) from exc
+        raise _caldav_discovery_http_error(exc) from exc
 
 
 @router.post("/caldav/sources", response_model=CalendarCalDavSourceResponse, status_code=status.HTTP_201_CREATED)