Fix default_order_by_id for association loading

The extension hooks into Dataset#all/each/first to inject ORDER BY id,
but Sequel's PlaceholderLiteralizer bypasses these methods entirely. It
pre-compiles SQL via Dataset#sql and calls with_sql_all directly, so
associations loaded through this optimized path had no deterministic
ordering.

Override placeholder_literalizer_loader to inject the ordering into the
dataset before it gets compiled into a reusable SQL template.

Author: philippthun

lib/sequel/extensions/default_order_by_id.rb

@@ -2,7 +2,8 @@
 
 # Sequel extension that adds default ORDER BY id to model queries.
 #
-# Hooks into fetch methods (all, each, first) to add ORDER BY id just before
+# Hooks into fetch methods (all, each, first) and placeholder_literalizer_loader
+# (used for optimized association loading) to add ORDER BY id just before
 # execution. This ensures ordering is only added to the final query, not to
 # subqueries or compound query parts.
 #
@@ -47,6 +48,13 @@ def first(*, &)
         ds.first(*, &)
       end
 
+      def placeholder_literalizer_loader(&block)
+        super do |pl, ds|
+          result_ds = block.call(pl, ds)
+          result_ds.send(:default_order_by_id) || result_ds
+        end
+      end
+
       private
 
       def default_order_by_id

spec/unit/lib/sequel/extensions/default_order_by_id_spec.rb

@@ -153,4 +153,30 @@ def capture_sql(&)
       end
     end
   end
+
+  describe 'association loading (placeholder_literalizer_loader)' do
+    let(:child_class) { Class.new(Sequel::Model(db[:test_default_order_join])) }
+
+    it 'adds ORDER BY id to association queries' do
+      child = child_class
+      parent_class = Class.new(Sequel::Model(db[:test_default_order_main])) do
+        one_to_many :children, class: child, key: :main_id
+      end
+      parent = parent_class.new
+      parent.values[:id] = 1
+      sql = capture_sql { parent.children }
+      expect(sql).to match(/ORDER BY .id./)
+    end
+
+    it 'does not override explicit association order' do
+      child = child_class
+      parent_class = Class.new(Sequel::Model(db[:test_default_order_main])) do
+        one_to_many :children, class: child, key: :main_id, order: Sequel.desc(:id)
+      end
+      parent = parent_class.new
+      parent.values[:id] = 1
+      sql = capture_sql { parent.children }
+      expect(sql).to match(/ORDER BY .id. DESC/)
+    end
+  end
 end