fix: sort persisters before concatenating with transformers

lib/spark/dsl/extension.ex

@@ -680,7 +680,7 @@ defmodule Spark.Dsl.Extension do
           |> Enum.flat_map(& &1.transformers())
           |> Transformer.sort()
           |> Enum.reject(& &1.after_compile?())
-          |> Enum.concat(Enum.flat_map(@extensions, & &1.persisters()))
+          |> Enum.concat(@extensions |> Enum.flat_map(& &1.persisters()) |> Transformer.sort())
         else
           []
         end

test/persister_sort_test.exs

@@ -0,0 +1,64 @@
+# SPDX-FileCopyrightText: 2026 spark contributors <https://github.com/ash-project/spark/graphs/contributors>
+#
+# SPDX-License-Identifier: MIT
+
+defmodule PersisterSortTest do
+  use ExUnit.Case
+
+  defmodule PersisterA do
+    use Spark.Dsl.Transformer
+
+    def transform(dsl) do
+      order = Spark.Dsl.Transformer.get_persisted(dsl, :persister_order, [])
+      {:ok, Spark.Dsl.Transformer.persist(dsl, :persister_order, order ++ [:a])}
+    end
+  end
+
+  defmodule PersisterB do
+    use Spark.Dsl.Transformer
+
+    def before?(PersisterSortTest.PersisterA), do: true
+    def before?(_), do: false
+
+    def transform(dsl) do
+      order = Spark.Dsl.Transformer.get_persisted(dsl, :persister_order, [])
+      {:ok, Spark.Dsl.Transformer.persist(dsl, :persister_order, order ++ [:b])}
+    end
+  end
+
+  defmodule PersisterC do
+    use Spark.Dsl.Transformer
+
+    def after?(PersisterSortTest.PersisterA), do: true
+    def after?(_), do: false
+
+    def transform(dsl) do
+      order = Spark.Dsl.Transformer.get_persisted(dsl, :persister_order, [])
+      {:ok, Spark.Dsl.Transformer.persist(dsl, :persister_order, order ++ [:c])}
+    end
+  end
+
+  defmodule Extension do
+    @section %Spark.Dsl.Section{
+      name: :test_section,
+      schema: []
+    }
+
+    use Spark.Dsl.Extension,
+      sections: [@section],
+      # Listed in reverse order to prove sorting works
+      persisters: [PersisterC, PersisterA, PersisterB]
+  end
+
+  defmodule TestDsl do
+    use Spark.Dsl, default_extensions: [extensions: PersisterSortTest.Extension]
+  end
+
+  defmodule TestResource do
+    use TestDsl
+  end
+
+  test "persisters are sorted based on before/after callbacks" do
+    assert Spark.Dsl.Extension.get_persisted(TestResource, :persister_order) == [:b, :a, :c]
+  end
+end