fix: empty milliseconds for utc datetime must have precision 6

fix: ensure actor & authorize? contexts are set even if not provided

lib/ash/actions/helpers.ex

@@ -97,7 +97,11 @@ defmodule Ash.Actions.Helpers do
     context = Process.get(:ash_context, %{}) || %{}
     private_context = Map.new(Keyword.take(opts, [:actor, :authorize?]))
 
-    context = Map.merge(context, private_context)
+    context =
+      context
+      |> Map.merge(private_context)
+      |> Map.put_new(:actor, nil)
+      |> Map.put_new(:authorize?, false)
 
     case query_or_changeset do
       %{__struct__: Ash.ActionInput} ->

lib/ash/type/datetime.ex

@@ -64,6 +64,20 @@ defmodule Ash.Type.DateTime do
     cast_input(%{datetime | microsecond: {0, 0}}, constraints)
   end
 
+  def cast_input(
+        %DateTime{microsecond: {0, 0}} = datetime,
+        [{:precision, :microsecond} | _] = constraints
+      ) do
+    cast_input(%{datetime | microsecond: {0, 6}}, constraints)
+  end
+
+  def cast_input(
+        %DateTime{microsecond: nil} = datetime,
+        [{:precision, :microsecond} | _] = constraints
+      ) do
+    cast_input(%{datetime | microsecond: {0, 6}}, constraints)
+  end
+
   def cast_input(value, constraints) do
     Ecto.Type.cast(storage_type(constraints), value)
   end