Fix app recovery when the whole runtime goes down

lib/livebook/session/data.ex

@@ -2507,7 +2507,7 @@ defmodule Livebook.Session.Data do
 
   Considers only cells that have already been evaluated.
   """
-  @spec cell_evaluation_parents(Data.t(), Cell.t()) :: list({Cell.t(), Section.t()})
+  @spec cell_evaluation_parents(t(), Cell.t()) :: list({Cell.t(), Section.t()})
   def cell_evaluation_parents(data, cell) do
     for {cell, section} <- Notebook.parent_cells_with_section(data.notebook, cell.id),
         info = data.cell_infos[cell.id],
@@ -2782,8 +2782,14 @@ defmodule Livebook.Session.Data do
   defp app_recover({data, _} = data_actions) do
     evaluable_cells_with_section = Notebook.evaluable_cells_with_section(data.notebook)
 
+    data_actions =
+      if data.runtime_status == :connected do
+        disconnect_runtime(data_actions)
+      else
+        data_actions
+      end
+
     data_actions
-    |> disconnect_runtime()
     |> connect_runtime()
     |> erase_outputs()
     |> garbage_collect_input_infos()

test/livebook/session/data_test.exs

@@ -4491,6 +4491,29 @@ defmodule Livebook.Session.DataTest do
                Data.apply_operation(data, operation)
     end
 
+    test "when fully executed and then runtime down, recovers by evaluating from scratch" do
+      data =
+        data_after_operations!(Data.new(mode: :app), [
+          {:insert_section, @cid, 0, "s1"},
+          {:insert_cell, @cid, "s1", 0, :code, "c1", %{}},
+          {:insert_cell, @cid, "s1", 1, :code, "c2", %{}},
+          connect_noop_runtime_operations(),
+          evaluate_cells_operations(["setup", "c1", "c2"])
+        ])
+
+      operation = {:runtime_down, @cid}
+
+      assert {:ok,
+              %{
+                cell_infos: %{
+                  "setup" => %{eval: %{status: :queued}},
+                  "c1" => %{eval: %{status: :queued}},
+                  "c2" => %{eval: %{status: :queued}}
+                },
+                app_data: %{status: %{execution: :executing}}
+              }, [:app_report_status, :connect_runtime]} = Data.apply_operation(data, operation)
+    end
+
     test "changes status back to :executed after recovery" do
       data =
         data_after_operations!(Data.new(mode: :app), [