what if we had a Message type[link]

1id: https://alice.social/activities/1
2actor: https://alice.social
3type: Message
4to: https://bob.social
5content: "hello bob"

1id: https://alice.social/activities/1
2actor: https://alice.social
3type: Message
4to: https://rooms.social/rooms/1/audience  # inbox forwarding, probably
5content: "hello room"
6context: https://rooms.social/rooms/1  # verify inclusion how?

1id: https://alice.social/activities/1
2actor: https://alice.social
3type: Message
4to: # inbox forwarding, definitely
5  - https://rooms.social/rooms/1  # we need to deliver to the room actor
6  - https://rooms.social/rooms/1/followers  # rooms.social or the room actor's client will forward to participants
7content: "hello room"
8context: https://rooms.social/rooms/1

1id: https://alice.social/activities/1
2actor: https://alice.social
3type: Message
4content: "hello room"  # arguably only the content needs to be signed? no need for canonicalization
5context: https://rooms.social/rooms/1