As a proof-of-concept implementation with Discourse, NodeBB will enable topic backfill via a resolvable context property.

• Each post (typically of type as:Note) will contain a context property that points to a resolvable activitypub object.

• This object is expected to be the topic containing the post, and should be of type Collection or OrderedCollection.

• Iterating through the pages of the collection should allow a server to remotely backfill an entire topic.

• This behaviour would take precedence over the fallback behaviour of inReplyTo traversal.

• as:Note provides context

• context resolves to a Collection (or OrderedCollection)

• Topic backfill with compatible NodeBB implementation

• Topic backfill with compatible Discourse implementation

• Discourse is able to backfill topics from compatible NodeBB implementation

Additional compatibility with FEP-7888:

• Resolved context contains an attributedTo (the category actor)
• Resolved context's attributedTo resolves to an Actor
• Upon receipt of object:
  • If context collection is retrieved and there are unprocessed items, send an Add activity out to category followers and post author
• Upon object creation:
  • When queried, object context is set to local instance context
  • Created object is sent to context authority for addition
  • When a corresponding Add activity is received referencing the created object, the object context can be updated