bxcore: a turn's speaker, SessionUpdated's turn, the session-state messages

Co-Authored-By: ornith-1.5-35b-a3b <agent@wntrmute.dev>

crates/bxcore/tests/turn_wire.rs

@@ -46,16 +46,46 @@ fn usage() -> Usage {
     }
 }
 
+/// A turn without a speaker has the bytes it had before M5c, and a frame without `speaker` reads
+/// as `None`: a turn with no speaker is never synced (M5c spec, section 4).
 #[test]
 fn turn() {
     let body = Turn {
         session: SessionId::new("chat-1789700000-42").unwrap(),
         content: "What time is it?".to_string(),
         resume: false,
+        speaker: None,
     };
     check("turn.json", env(3, true, Message::Turn(body)));
 }
 
+/// The speaker is written last, when there is one (M5c spec, section 11).
+#[test]
+fn turn_with_a_speaker() {
+    let body = Turn {
+        session: SessionId::new("mm-r0000000000000000000000001").unwrap(),
+        content: "What time is it?".to_string(),
+        resume: true,
+        speaker: Some("kyle".to_string()),
+    };
+    check("turn_speaker.json", env(3, true, Message::Turn(body)));
+}
+
+/// `bxcore` does not check a speaker's name: `memoryd` checks it against Honcho's pattern (M5c
+/// spec, section 3). A Mattermost username with a `.` is carried as it is.
+#[test]
+fn a_speaker_is_carried_as_it_is() {
+    let body = Turn {
+        session: SessionId::new("mm-r0000000000000000000000001").unwrap(),
+        content: "hi".to_string(),
+        resume: false,
+        speaker: Some("first.last".to_string()),
+    };
+    let text = serde_json::to_string(&body).unwrap();
+    assert!(text.ends_with(r#","speaker":"first.last"}"#), "{text}");
+    assert_eq!(serde_json::from_str::<Turn>(&text).unwrap(), body);
+}
+
 #[test]
 fn turn_events() {
     check(
@@ -262,6 +292,7 @@ fn usage_records() {
         LogRecord::User {
             time: Timestamp::parse("2026-09-18T08:05:01.000Z").unwrap(),
             content: "What time is it?".to_string(),
+            speaker: None,
         },
         LogRecord::Assistant {
             time: Timestamp::parse("2026-09-18T08:05:03.000Z").unwrap(),