ActivityPub Create activity with multiple objects

Steps to reproduce the problem

Multiple objects (that is, an array of objects) in a Create activity is valid under the W3C Activity Vocabulary recommendation.

{
"@context":"https://www.w3.org/ns/activitystreams",
"id":"https://example.org/activities/1",
"type":"Create",
"actor":"https://example.org/actors/someone",
"to":"https://mastodon.social/users/someone-else",
"object": [
 {
  "@context":"https://www.w3.org/ns/activitystreams",
  "id":"https://example.org/objects/notes/1",
  "type":"Note",
  "attributedTo":"https://example.org/actors/someone",
  "content":"<p>1/2 Hello</p>",
  "audience":"https://www.w3.org/ns/activitystreams#Public"
 },
 {
  "@context":"https://www.w3.org/ns/activitystreams",
  "id":"https://example.org/objects/notes/2",
  "type":"Note",
  "attributedTo":"https://example.org/actors/someone",
  "content":"<p>2/2 world</p>",
  "audience":"https://www.w3.org/ns/activitystreams#Public"
 }
]
}

It was suggested in discussion of another issue that such a construct might be used to implement a feature analogous to a "twitter storm".

Expected behaviour

Minimally, as a result of such a Create arriving in a Mastodon inbox, the multiple notes should be ingested as if the single Create activity were split into separate activities, each with a single Note object. Extra credit points if the Mastodon UI indicates that the two notes were in sequence, perhaps obviating the 1/2 and 2/2 in the text of the notes in the example.

Actual behaviour

Though Mastodon accepted the construct with a 202, neither Note appeared in the timeline.

Specifications

Version of Mastodon deployed on mastodon.social, Sep 3.

mastodon / mastodon