Add Codex JSON sessions and usage limits

server/src/session/driver.rs

@@ -498,9 +498,9 @@ pub type EventSink = mpsc::UnboundedSender<Event>;
 /// The inbound half of a session. Deliberately small; see PLAN.md for the
 /// per-driver mapping of each method onto its dialect.
 ///
-/// `send_user_message` during a run is the point of the whole app: both
-/// real dialects queue it for injection at the next tool boundary rather
-/// than the end of the turn.
+/// `send_user_message` during a run is the point of the whole app: a dialect
+/// with live input injects it at the next tool boundary, while a turn-at-a-time
+/// dialect queues it for the next child process.
 pub trait Driver: Send + Sync {
     /// Takes a message, now or once the session is free for it.
     ///