Improve errors on reconnecting Mix runtime (#837)

lib/livebook/runtime/mix_standalone.ex

@@ -83,9 +83,23 @@ defmodule Livebook.Runtime.MixStandalone do
 
     init_async(project_path, emitter)
 
+    await_init(ref, [])
+  end
+
+  defp await_init(ref, outputs) do
     receive do
-      {:emitter, ^ref, {:ok, runtime}} -> {:ok, runtime}
+      {:emitter, ^ref, message} -> message
-      {:emitter, ^ref, {:error, error}} -> {:error, error}
+    end
+    |> case do
+      {:ok, runtime} ->
+        {:ok, runtime}
+
+      {:error, error} ->
+        message = IO.iodata_to_binary([error, ". Output:\n\n", Enum.reverse(outputs)])
+        {:error, message}
+
+      {:output, output} ->
+        await_init(ref, [output | outputs])
     end
   end
 
@@ -98,7 +112,7 @@ defmodule Livebook.Runtime.MixStandalone do
            into: output_emitter
          ) do
       {_callback, 0} -> :ok
-      {_callback, _status} -> {:error, "running mix #{task} failed, see output for more details"}
+      {_callback, _status} -> {:error, "running mix #{task} failed"}
     end
   end
 

lib/livebook_web/live/session_live.ex

@@ -741,7 +741,7 @@ defmodule LivebookWeb.SessionLive do
         case Runtime.duplicate(runtime) do
           {:ok, new_runtime} ->
             Session.connect_runtime(socket.assigns.session.pid, new_runtime)
-            socket
+            clear_flash(socket, :error)
 
           {:error, message} ->
             put_flash(socket, :error, "Failed to setup runtime - #{message}")

lib/livebook_web/templates/layout/live.html.heex

@@ -1,5 +1,5 @@
 <main role="main" class="flex-grow flex flex-col h-screen">
-  <div class="fixed right-8 bottom-5 z-50 flex flex-col space-y-3">
+  <div class="fixed right-8 bottom-5 z-50 flex flex-col space-y-3 max-h-[80%] overflow-y-auto tiny-scrollbar">
     <%= if live_flash(@flash, :info) do %>
       <div class="shadow-custom-1 max-w-2xl flex items-center space-x-3 rounded-lg px-4 py-2 border-l-4 rounded-l-none border-blue-500 bg-white text-gray-600 hover:bg-gray-50 hover:text-gray-500 cursor-pointer" role="alert"
         phx-click="lv:clear-flash"