fix(streaming): ensure [DONE] SSE marker uses correct error type

src/server/mod.rs

@@ -283,7 +283,9 @@ 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::default().data("[DONE]")) });
+                let done = futures::stream::once(async {
+                    Ok::<Event, AppError>(Event::default().data("[DONE]"))
+                });
                 let out = sse_stream.chain(done);
 
                 Ok(