Reuse epoch-verified record snapshots and avoid empty push payloads

app/models/record_cache.rb

@@ -0,0 +1,24 @@
+# Rebuild request-local models from bounded, immutable database snapshots.
+# The observer must still see the captured epoch after lookup and admission.
+class RecordCache
+  def self.fetch(key, version)
+    return yield unless version && ResponseCache.instance.budget.positive? && !ActiveRecord::Base.connection.transaction_open?
+
+    key = ActiveSupport::Cache.expand_cache_key([ "record-snapshot-v1", version, key ])
+    return yield if key.bytesize > ResponseCache::MAX_KEY_BYTES
+
+    if snapshot = FragmentCache.store.read(key)
+      if ResponseCache.instance.version == version
+        return ActiveSupport::JSON.decode(snapshot).map { |name, attributes| name.constantize.instantiate(attributes) }
+      end
+    end
+
+    records = yield
+    if records.all? { |record| record&.persisted? && !record.changed? } && ResponseCache.instance.version == version
+      # Raw database values retain timestamp precision and native enum binding.
+      snapshot = ActiveSupport::JSON.encode(records.map { |record| [ record.class.name, record.attributes_before_type_cast ] })
+      FragmentCache.store.write(key, snapshot) if snapshot.bytesize <= ResponseCache::MAX_ENTRY_BYTES
+    end
+    records
+  end
+end

app/models/room/message_pusher.rb

@@ -6,9 +6,9 @@ class Room::MessagePusher
   end
 
   def push
-    build_payload.tap do |payload|
-      push_to_users_involved_in_everything(payload)
-      push_to_users_involved_in_mentions(payload)
+    subscriptions = push_subscriptions_for_users_involved_in_everything.or(push_subscriptions_for_mentionable_users(message.mentionees))
+    if subscriptions.exists?
+      Rails.configuration.x.web_push_pool.queue(build_payload, subscriptions)
     end
   end
 
@@ -37,14 +37,6 @@ class Room::MessagePusher
       }
     end
 
-    def push_to_users_involved_in_everything(payload)
-      enqueue_payload_for_delivery payload, push_subscriptions_for_users_involved_in_everything
-    end
-
-    def push_to_users_involved_in_mentions(payload)
-      enqueue_payload_for_delivery payload, push_subscriptions_for_mentionable_users(message.mentionees)
-    end
-
     def push_subscriptions_for_users_involved_in_everything
       relevant_subscriptions.merge(Membership.involved_in_everything)
     end
@@ -59,10 +51,6 @@ class Room::MessagePusher
       Push::Subscription
         .joins(user: :memberships)
         .merge(User.active)
-        .merge(Membership.visible.disconnected.where(room: room).where.not(user: message.creator))
-    end
-
-    def enqueue_payload_for_delivery(payload, subscriptions)
-      Rails.configuration.x.web_push_pool.queue(payload, subscriptions)
+        .merge(Membership.visible.disconnected.where(room: room).where.not(user_id: message.creator_id))
     end
 end