fix(streaming): use iter instead of once for [DONE] marker

src/server/mod.rs

@@ -283,10 +283,10 @@ async fn chat_completions(
                 // Many OpenAI-compatible clients expect a terminal [DONE] marker.
                 // Emit it when the upstream stream ends to avoid clients treating
                 // the response as incomplete.
-                let done = futures::stream::once(async {
-                    Ok::<Event, AppError>(Event::default().data("[DONE]"))
-                });
-                let out = sse_stream.chain(done);
+                // Convert to a Vec first, then append [DONE], then stream it
+                let done_event = Ok::<Event, AppError>(Event::default().data("[DONE]"));
+                let done_stream = futures::stream::iter(vec![done_event]);
+                let out = sse_stream.chain(done_stream);
 
                 Ok(
                     Sse::new(out)