Bump protocol to v9 and carry talk-circle ids on the presence frame.

Names stay off the wire; a person not in a circle writes an empty member list and topic.

Co-authored-by: Cursor <cursoragent@cursor.com>

src/HSchool.Protocol/Messages.cs

@@ -98,8 +98,22 @@ public sealed record PresenceNode(
     string ActivitySubject = "",
     string ActivityClass = "");
 
-/// <summary>One on-campus person. Names are resolved over HTTP, not on this frame.</summary>
-public sealed record PresencePerson(string Id, string NodeId, byte State);
+/// <summary>
+/// One on-campus person. Names are resolved over HTTP, not on this frame. Talk members and
+/// topic are ids; an empty list means the person is not in a circle.
+/// </summary>
+public sealed record PresencePerson(
+    string Id,
+    string NodeId,
+    byte State,
+    IReadOnlyList<string> TalkMemberIds,
+    string TalkTopicId)
+{
+    public PresencePerson(string id, string nodeId, byte state)
+        : this(id, nodeId, state, [], "")
+    {
+    }
+}
 
 /// <summary>
 /// Live occupancy of an open school, about twice a second. Counts and people cover the whole

src/HSchool.Protocol/ProtocolCodec.cs

@@ -202,6 +202,14 @@ public static class ProtocolCodec
         foreach (var person in message.People)
         {
             size += StringSize(person.Id) + StringSize(person.NodeId) + sizeof(byte);
+            var members = person.TalkMemberIds ?? [];
+            size += sizeof(byte);
+            foreach (var memberId in members)
+            {
+                size += StringSize(memberId);
+            }
+
+            size += StringSize(person.TalkTopicId ?? "");
         }
 
         return size;
@@ -242,9 +250,22 @@ public static class ProtocolCodec
         writer.WriteUInt16((ushort)message.People.Count);
         foreach (var person in message.People)
         {
+            var members = person.TalkMemberIds ?? [];
+            if (members.Count > byte.MaxValue)
+            {
+                throw new ProtocolException($"Presence person {person.Id} has {members.Count} talk members; u8 count cannot hold it.");
+            }
+
             writer.WriteString(person.Id);
             writer.WriteString(person.NodeId);
             writer.WriteByte(person.State);
+            writer.WriteByte((byte)members.Count);
+            foreach (var memberId in members)
+            {
+                writer.WriteString(memberId);
+            }
+
+            writer.WriteString(person.TalkTopicId ?? "");
         }
 
         return writer.Position;
@@ -403,7 +424,18 @@ public static class ProtocolCodec
         var people = new PresencePerson[personCount];
         for (var i = 0; i < personCount; i++)
         {
-            people[i] = new PresencePerson(reader.ReadString(), reader.ReadString(), reader.ReadByte());
+            var id = reader.ReadString();
+            var nodeId = reader.ReadString();
+            var state = reader.ReadByte();
+            var memberCount = reader.ReadByte();
+            var members = new string[memberCount];
+            for (var member = 0; member < memberCount; member++)
+            {
+                members[member] = reader.ReadString();
+            }
+
+            var topicId = reader.ReadString();
+            people[i] = new PresencePerson(id, nodeId, state, members, topicId);
         }
 
         return new ServerPresenceMessage(schoolId, nodes, people);

src/HSchool.Protocol/ProtocolConstants.cs

@@ -4,7 +4,7 @@ namespace HSchool.Protocol;
 public static class ProtocolConstants
 {
     /// <summary>Bumped on every breaking change to the binary layout.</summary>
-    public const byte Version = 8;
+    public const byte Version = 9;
 
     /// <summary>Upper bound for a single WebSocket frame accepted by the server.</summary>
     public const int MaxMessageSize = 8 * 1024;