[FIX] export_bg: Handle import_compat parameter correctly in background export

When import_compat=False, avoid using field 'value' for data extraction
to prevent issues when the exported data is used for record updates.

- In import_compat mode: use name -> value -> id fallback chain
- In regular export mode: use only name -> id (skip 'value')
- Field labels (headers) are handled appropriately for each mode

This ensures exported data maintains proper field references based on
the intended use case (import vs display/update).

closes #367

Signed-off-by: Franco Leyes <lef@adhoc.com.ar>

Author: rov-adhoc

export_bg/models/export_bg_mixin.py

@@ -39,8 +39,18 @@ def _export_chunk_bg(self, data, export_id, export_format):
                 ]
             )
 
-        field_names = [f.get("name") or f.get("value") or f.get("id") for f in params["fields"]]
-        field_labels = [f.get("label") or f.get("string") for f in params["fields"]]
+        # Extract field names considering import_compat mode
+        import_compat = params.get("import_compat", True)
+
+        # For field_names (data extraction), always use the technical field name
+        # Only use 'value' as fallback when import_compat=True (for import compatibility)
+        if import_compat:
+            field_names = [f.get("name") or f.get("value") or f.get("id") for f in params["fields"]]
+            field_labels = field_names  # Use field names as headers for import compatibility
+        else:
+            # When not import_compat, use only 'name' or 'id' for field_names, not 'value'
+            field_names = [f.get("name") or f.get("id") for f in params["fields"]]
+            field_labels = [f.get("label") or f.get("string") for f in params["fields"]]
 
         export_data = self.export_data(field_names).get("datas", [])