fixes and refactor

app/middleware/errors.py

@@ -46,6 +46,25 @@ def _get_correlation_id(request: Request) -> str:
     return str(uuid4())
 
 
+def _json_safe(value: Any) -> Any:
+    """Recursively convert non-JSON-serializable objects (like Exceptions) into strings.
+
+    Keeps overall structure intact so tests inspecting error details (e.g. 'loc', 'msg') still work.
+    """
+    # Exception -> string message
+    if isinstance(value, BaseException):
+        return str(value)
+    # Mapping types
+    if isinstance(value, dict):
+        return {k: _json_safe(v) for k, v in value.items()}
+    # Sequence types
+    if isinstance(value, (list, tuple)):
+        return [
+            _json_safe(v) for v in value
+        ]
+    return value
+
+
 def _build_error_response(
     request: Request,
     *,
@@ -66,7 +85,7 @@ def _build_error_response(
         "correlation_id": correlation_id,
     }
     if details is not None:
-        body["error"]["details"] = details
+        body["error"]["details"] = _json_safe(details)
 
     response = JSONResponse(content=body, status_code=status_code)
     response.headers[ERROR_HEADER_NAME] = correlation_id