One program

// THE PAGE — and it is small on purpose. Everything interesting about this spike is in what the page does NOT say.

[Page("/")]
[Render(CSR)]
[Title("The room")]
component Room() {
  Guid roomId = Guid.Empty;

1  string draft = "";

2  live var messages = Message
    .Where(m => m.Conversation.Id == roomId)
3    .Include(m => m.Author)
    .OrderBy(m => m.SentAt)
    .ToList();

4  on mount { roomId = JoinTheRoom(); }

5  action Send() {
6    Say(roomId, draft);
    draft = "";
  }

7  render {
    Stack(gap: 4, p: 6, maxW: "720px", bg: Colors.Bg, color: Colors.OnBg, minH: "100vh") {
      Text("The room", fontSize: FontSize.Hero, fontWeight: FontWeight.Medium);
      // The viewer's scalar fields ride the boot bag, so this is CLIENT state and costs no query.
      // Binding the whole entity (`var me = Session.CurrentUser;`) would have been a server read —
      // the row under this app's security — to render one string the browser already had.
8      Text("Signed in as " + Session.CurrentUser.Email, fontSize: FontSize.Caption, color: Colors.TextMuted);

      Stack(gap: 2) {
9        foreach (var m in messages) {
          Row(gap: 2) {
            Text(m.Author.Email + ":", fontWeight: FontWeight.Medium);
            Text(m.Body);
          }
        }
      }

      Row(gap: 2) {
        Input(value: draft, label: "Message", placeholder: "say something");
        Osyrin.Button("Send", onClick: Send);
      }
    }
  }
}

entity Conversation {
1  [Required][MaxLength(120)] string Topic;
  [Required] DateTime StartedAt;
2  security {
    allow read, create when IsAuthenticated;
  }
}

entity Participant {
  [Required] Conversation Conversation;
  [Required] User Person;
  [Required] DateTime JoinedAt;
  security {
3    allow read where Participant.Any(p => p.Conversation == Conversation && p.Person == user);
    allow create where Person == user;
  }
}

entity Message {
  [Required] Conversation Conversation;
  [Required] User Author;
  [Required][MaxLength(2000)] string Body;
  [Required] DateTime SentAt;
  security {
    allow read where Participant.Any(p => p.Conversation == Conversation && p.Person == user);
    allow create where Author == user
                    && Participant.Any(p => p.Conversation == Conversation && p.Person == user);
  }

Guid JoinTheRoom() {
1  var room = Conversation.OrderBy(c => c.StartedAt).FirstOrDefault();
  if (room == null) {
2    room = new Conversation { Topic = "The room", StartedAt = DateTime.UtcNow };
  }

  var me = Session.CurrentUser;
  if (!Participant.Any(p => p.Conversation == room && p.Person == me)) {
    new Participant { Conversation = room, Person = me, JoinedAt = DateTime.UtcNow };
  }

3  UnitOfWork.Commit();
  return room.Id;
}