fix(activitypub): refetch a stale Move target once

A Move usually follows right after the alias was added, and the cached
remote target may not have it yet. Refetch the target when the alias is
missing instead of rejecting the Move. Same issue as Akkoma f18e2ba42.

test/pleroma/web/activity_pub/transmogrifier_test.exs

@@ -147,6 +147,53 @@ defmodule Pleroma.Web.ActivityPub.TransmogrifierTest do
       assert activity.data["type"] == "Move"
     end
 
+    test "it refetches a cached remote Move target that lacks the alias" do
+      old_user = insert(:user, local: false, ap_id: "https://old.example/users/old")
+
+      new_user =
+        insert(:user,
+          local: false,
+          ap_id: "https://new.example/users/new",
+          nickname: "new@new.example",
+          last_refreshed_at: NaiveDateTime.utc_now()
+        )
+
+      actor = %{
+        "@context" => "https://www.w3.org/ns/activitystreams",
+        "id" => new_user.ap_id,
+        "type" => "Person",
+        "preferredUsername" => "new",
+        "inbox" => new_user.ap_id <> "/inbox",
+        "outbox" => new_user.ap_id <> "/outbox",
+        "followers" => new_user.ap_id <> "/followers",
+        "following" => new_user.ap_id <> "/following",
+        "alsoKnownAs" => [old_user.ap_id]
+      }
+
+      Tesla.Mock.mock(fn
+        %{method: :get, url: "https://new.example/users/new"} ->
+          %Tesla.Env{
+            status: 200,
+            headers: [{"content-type", "application/activity+json"}],
+            body: Jason.encode!(actor)
+          }
+
+        _ ->
+          %Tesla.Env{status: 404}
+      end)
+
+      message = %{
+        "@context" => "https://www.w3.org/ns/activitystreams",
+        "type" => "Move",
+        "actor" => old_user.ap_id,
+        "object" => old_user.ap_id,
+        "target" => new_user.ap_id
+      }
+
+      assert {:ok, %Activity{data: %{"type" => "Move"}}} = Transmogrifier.handle_incoming(message)
+      assert old_user.ap_id in User.get_cached_by_ap_id(new_user.ap_id).also_known_as
+    end
+
     test "it fixes both the Create and object contexts in a reply" do
       insert(:user, ap_id: "https://mk.absturztau.be/users/8ozbzjs3o8")
       insert(:user, ap_id: "https://p.helene.moe/users/helene")