register and sign in pages

backend/core/exceptions.py

@@ -0,0 +1,32 @@
+"""A single response shape for every error the API returns.
+
+    {"detail": "...", "code": "...", "errors": {"field": ["..."]}}
+
+`errors` is only present for validation failures. The SPA reads `code` to
+branch (e.g. `registration_required`) and `detail` to show a message.
+"""
+
+from rest_framework import exceptions
+from rest_framework.views import exception_handler as drf_exception_handler
+
+
+def exception_handler(exc, context):
+    response = drf_exception_handler(exc, context)
+    if response is None:
+        return None
+
+    code = getattr(exc, "default_code", "error")
+    data = response.data
+
+    if isinstance(exc, exceptions.ValidationError):
+        detail = "The submitted data was invalid."
+        if isinstance(data, dict):
+            non_field = data.get("detail") or data.get("non_field_errors")
+            if non_field:
+                detail = non_field[0] if isinstance(non_field, list) else str(non_field)
+        response.data = {"detail": str(detail), "code": code, "errors": data}
+        return response
+
+    detail = data.get("detail") if isinstance(data, dict) else data
+    response.data = {"detail": str(detail), "code": code}
+    return response