Fix concat_on_disk

src/anndata/experimental/merge.py

@@ -371,13 +371,13 @@
 
 
 def _write_alt_mapping(groups, output_group, alt_axis_name, alt_indices, merge):
-    alt_mapping = merge([read_as_backed(g[alt_axis_name]) for g in groups])
+    alt_mapping = merge([read_as_backed(g[f"{alt_axis_name}m"]) for g in groups])
     # If its empty, we need to write an empty dataframe with the correct index
     if not alt_mapping:
         alt_df = pd.DataFrame(index=alt_indices)
-        write_elem(output_group, alt_axis_name, alt_df)
+        write_elem(output_group, f"{alt_axis_name}m", alt_df)
     else:
-        write_elem(output_group, alt_axis_name, alt_mapping)
+        write_elem(output_group, f"{alt_axis_name}m", alt_mapping)
 
 
 def _write_alt_annot(groups, output_group, alt_axis_name, alt_indices, merge):
@@ -402,6 +402,11 @@
     write_elem(output_group, axis_name, concat_annot)
 
 
+def _write_uns(groups, output_group, merge):
+    uns = merge([read_elem(g["uns"]) for g in groups])
+    write_elem(output_group, "uns", uns)
+
+
 def concat_on_disk(
     in_files: Collection[str | os.PathLike] | Mapping[str, str | os.PathLike],
     out_file: str | os.PathLike,
@@ -633,6 +638,9 @@
     # Write {alt_axis_name}m
     _write_alt_mapping(groups, output_group, alt_axis_name, alt_index, merge)
 
+    # Write uns
+    _write_uns(groups, output_group, uns_merge)
+
     # Write X
 
     _write_concat_arrays(