fix: update_project_metadata keeps fields absent from attrs instead of resetting them

lib/bds/metadata.ex

@@ -318,6 +318,8 @@ defmodule BDS.Metadata do
     }
   end
 
+  # Keys absent from attrs are left out entirely, so the merge in
+  # update_project_metadata/2 keeps their current values (partial update).
   defp normalize_project_metadata_attrs(attrs, project) do
     %{
       name: attr(attrs, :name) || project.name,
@@ -333,6 +335,26 @@ defmodule BDS.Metadata do
       semantic_similarity_enabled: attr(attrs, :semantic_similarity_enabled) || false,
       blog_languages: normalize_language_list(attr(attrs, :blog_languages) || [])
     }
+    |> Map.take(present_attr_keys(attrs))
+  end
+
+  defp present_attr_keys(attrs) do
+    Enum.filter(
+      [
+        :name,
+        :description,
+        :public_url,
+        :main_language,
+        :default_author,
+        :max_posts_per_page,
+        :image_import_concurrency,
+        :blogmark_category,
+        :pico_theme,
+        :semantic_similarity_enabled,
+        :blog_languages
+      ],
+      fn key -> Map.has_key?(attrs, key) or Map.has_key?(attrs, Atom.to_string(key)) end
+    )
   end
 
   defp normalize_category_settings(settings) do

lib/bds/scripting/api_docs.ex

@@ -762,7 +762,8 @@ defmodule BDS.Scripting.ApiDocs do
     %{
       module: "meta",
       name: "update_project_metadata",
-      description: "Update metadata for the current project.",
+      description:
+        "Update metadata for the current project. Keys omitted from updates keep their current values.",
       params: [%{name: "updates", type: "table", required: true}],
       returns: "ProjectMetadata | nil"
     },

lib/bds/ui/settings_form.ex

@@ -388,30 +388,8 @@ defmodule BDS.UI.SettingsForm do
     )
   end
 
-  # Project, technology and style all live in the same metadata record;
-  # `Metadata.update_project_metadata/2` treats missing keys as nil, so the
-  # current values are always passed along and only the edits override them.
   defp save_project_metadata(project_id, overrides) do
-    {:ok, metadata} = Metadata.get_project_metadata(project_id)
-
-    attrs =
-      metadata
-      |> Map.take([
-        :name,
-        :description,
-        :public_url,
-        :main_language,
-        :default_author,
-        :max_posts_per_page,
-        :image_import_concurrency,
-        :blogmark_category,
-        :pico_theme,
-        :semantic_similarity_enabled,
-        :blog_languages
-      ])
-      |> Map.merge(overrides)
-
-    case Metadata.update_project_metadata(project_id, attrs) do
+    case Metadata.update_project_metadata(project_id, overrides) do
       {:ok, _metadata} -> :ok
       {:error, reason} -> {:error, reason}
     end