Account for last token count on resume (#8677)

last token count in context manager is initialized to 0. Gets populated
only on events from server.

This PR populates it on resume so we can decide if we need to compact or
not.

codex-rs/core/src/codex_delegate.rs

@@ -184,6 +184,10 @@ async fn forward_events(
                         id: _,
                         msg: EventMsg::AgentMessageDelta(_) | EventMsg::AgentReasoningDelta(_),
                     } => {}
+                    Event {
+                        id: _,
+                        msg: EventMsg::TokenCount(_),
+                    } => {}
                     Event {
                         id: _,
                         msg: EventMsg::SessionConfigured(_),