Rework FEP-7888 implementation (#36064)

app/controllers/activitypub/contexts_controller.rb

@@ -26,7 +26,8 @@ class ActivityPub::ContextsController < ActivityPub::BaseController
   end
 
   def set_conversation
-    @conversation = Conversation.local.find(params[:id])
+    account_id, status_id = params[:id].split('-')
+    @conversation = Conversation.local.find_by(parent_account_id: account_id, parent_status_id: status_id)
   end
 
   def set_items

app/lib/activitypub/tag_manager.rb

@@ -41,7 +41,7 @@ class ActivityPub::TagManager
     when :person
       target.instance_actor? ? instance_actor_url : account_url(target)
     when :conversation
-      context_url(target)
+      context_url(target) unless target.parent_account_id.nil? || target.parent_status_id.nil?
     when :note, :comment, :activity
       return activity_account_status_url(target.account, target) if target.reblog?
 

app/models/conversation.rb

@@ -24,6 +24,10 @@ class Conversation < ApplicationRecord
 
   before_validation :set_parent_account, on: :create
 
+  def to_param
+    "#{parent_account_id}-#{parent_status_id}" unless parent_account_id.nil? || parent_status_id.nil?
+  end
+
   def local?
     uri.nil?
   end

app/presenters/activitypub/context_presenter.rb

@@ -7,7 +7,7 @@ class ActivityPub::ContextPresenter < ActiveModelSerializers::Model
     def from_conversation(conversation)
       new.tap do |presenter|
         presenter.id = ActivityPub::TagManager.instance.uri_for(conversation)
-        presenter.attributed_to = ActivityPub::TagManager.instance.uri_for(conversation.parent_account)
+        presenter.attributed_to = ActivityPub::TagManager.instance.uri_for(conversation.parent_account) if conversation.parent_account.present?
       end
     end
   end

app/serializers/activitypub/note_serializer.rb

@@ -2,6 +2,7 @@
 
 class ActivityPub::NoteSerializer < ActivityPub::Serializer
   include FormattingHelper
+  include JsonLdHelper
 
   context_extensions :atom_uri, :conversation, :sensitive, :voters_count, :quotes, :interaction_policies
 
@@ -159,14 +160,16 @@ class ActivityPub::NoteSerializer < ActivityPub::Serializer
     if object.conversation.uri?
       object.conversation.uri
     else
-      OStatus::TagManager.instance.unique_tag(object.conversation.created_at, object.conversation.id, 'Conversation')
+      # This means `parent_status_id` and `parent_account_id` must *not* get backfilled
+      ActivityPub::TagManager.instance.uri_for(object.conversation) || OStatus::TagManager.instance.unique_tag(object.conversation.created_at, object.conversation.id, 'Conversation')
     end
   end
 
   def context
     return if object.conversation.nil?
 
-    ActivityPub::TagManager.instance.uri_for(object.conversation)
+    uri = ActivityPub::TagManager.instance.uri_for(object.conversation)
+    uri unless unsupported_uri_scheme?(uri)
   end
 
   def local?