Refresh on models etag mismatch (#8491)

- Send models etag
- Refresh models on 412
- This wires `ModelsManager` to `ModelFamily` so we don't mutate it
mid-turn

codex-rs/codex-api/src/endpoint/chat.rs

@@ -152,6 +152,9 @@ impl Stream for AggregatedStream {
                 Poll::Ready(Some(Ok(ResponseEvent::RateLimits(snapshot)))) => {
                     return Poll::Ready(Some(Ok(ResponseEvent::RateLimits(snapshot))));
                 }
+                Poll::Ready(Some(Ok(ResponseEvent::ModelsEtag(etag)))) => {
+                    return Poll::Ready(Some(Ok(ResponseEvent::ModelsEtag(etag))));
+                }
                 Poll::Ready(Some(Ok(ResponseEvent::Completed {
                     response_id,
                     token_usage,