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

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

crates/loopd/src/turn.rs

@@ -123,6 +123,9 @@ pub fn run_turn(
         .append(LogRecord::User {
             time: Timestamp::now(),
             content: neutralise(content).into_owned(),
+            // Set in M5c-1 task 02, from the turn. `None` is not written: the record's bytes
+            // are as before.
+            speaker: None,
         })
         .map_err(TurnError::Session)?;