bxctl: chat --speaker NAME, the speaker on every turn of the chat

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

crates/bxctl/src/chat.rs

@@ -73,12 +73,14 @@ pub fn new_session_id() -> SessionId {
     SessionId::new(&candidate).unwrap_or_else(|_| SessionId::new("chat-0-0").unwrap_or_default())
 }
 
-/// Sends one turn and reads the reply. `on_event` sees every event frame as it arrives.
+/// Sends one turn and reads the reply. `on_event` sees every event frame as it arrives. `speaker`
+/// is `--speaker`'s value, sent as it is; `None` sends none.
 pub fn run_turn(
     socket: &Path,
     session: &SessionId,
     content: &str,
     resume: bool,
+    speaker: Option<&str>,
     on_event: &mut dyn FnMut(&TurnEvent),
 ) -> Result<TurnDone, ChatError> {
     let mut stream = UnixStream::connect(socket).map_err(ChatError::Connect)?;
@@ -87,8 +89,7 @@ pub fn run_turn(
         session: session.clone(),
         content: content.to_string(),
         resume,
-        // Set in M5c-1 task 04, from `--speaker`. Until then no turn has a speaker.
-        speaker: None,
+        speaker: speaker.map(str::to_string),
     };
     write_frame(
         &mut stream,
@@ -324,11 +325,12 @@ pub fn stream_turn(
     session: &SessionId,
     text: &str,
     resume: bool,
+    speaker: Option<&str>,
     approvals: &Approvals<'_>,
     io: &mut TurnIo<'_>,
 ) -> std::io::Result<Result<TurnDone, ChatError>> {
     let mut err = None;
-    let outcome = run_turn(socket, session, text, resume, &mut |event| {
+    let outcome = run_turn(socket, session, text, resume, speaker, &mut |event| {
         if err.is_some() {
             return;
         }