Delete a room's messages in a job, one transaction each

Room#destroy destroyed every message inside the room's own
transaction, which holds SQLite's write lock until the last one: on a
room with many messages, every other write in the app waited and
failed. The request now takes the room away from its members and
leaves the rest to Room::DestroyJob, which destroys the messages one
at a time, each in its own short transaction, and then the room.

An open room is closed in the request, so that someone who joins the
account before the job ends isn't given it.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bj8KnxpTf9sj2Ysa8aLAVa

app/controllers/rooms_controller.rb

@@ -12,7 +12,7 @@ class RoomsController < ApplicationController
   end
 
   def destroy
-    @room.destroy
+    @room.destroy_later
 
     broadcast_remove_room
     redirect_to root_url

app/jobs/room/destroy_job.rb

@@ -0,0 +1,7 @@
+class Room::DestroyJob < ApplicationJob
+  discard_on ActiveJob::DeserializationError
+
+  def perform(room)
+    room.destroy_one_message_at_a_time
+  end
+end

app/models/room.rb

@@ -45,6 +45,27 @@ class Room < ApplicationRecord
     end
   end
 
+  # Takes the room away from its members at once, and leaves its messages to Room::DestroyJob. Destroying them in
+  # the room's own transaction held the database's write lock, and stopped every other write, until the last one.
+  # An open room is closed first, so that no one who joins the account before the job runs is let in.
+  def destroy_later
+    room = open? ? becomes!(Rooms::Closed) : self
+
+    transaction do
+      room.save!
+      room.memberships.delete_all
+    end
+
+    Room::DestroyJob.perform_later(room)
+  end
+
+  # Each message is destroyed in its own transaction, so other writes get through in between. Any message posted
+  # meanwhile goes with the room.
+  def destroy_one_message_at_a_time
+    messages.find_each(&:destroy)
+    destroy
+  end
+
   def receive(message)
     unread_memberships(message)
     push_later(message)