Handle missing streamed token metrics

src/aituner/http_client.py

@@ -310,7 +310,7 @@ def stream_chat_completion(
     return StreamMetrics(
         ttft_ms=ttft_ms,
         tpot_ms=tpot_ms,
-        completion_tokens=used_tokens if used_tokens > 0 else None,
+        completion_tokens=used_tokens if used_tokens is not None and used_tokens > 0 else None,
         completion_tokens_source=completion_tokens_source,
         streamed_chunk_count=chunk_token_count,
     )

src/aituner/worker.py

@@ -8,6 +8,7 @@ import statistics
 import subprocess
 import threading
 import time
+import traceback
 from concurrent.futures import FIRST_COMPLETED, Future, ThreadPoolExecutor, wait
 from dataclasses import dataclass
 from pathlib import Path
@@ -596,6 +597,7 @@ def run_trial(trial_spec_path: Path) -> dict[str, Any]:
                 "best_request_count": None,
                 "failure_stage": failure_stage,
                 "failure_reason": str(exc),
+                "failure_traceback": traceback.format_exc(),
                 "probes": probe_history,
             }
             StudyStore.write_json(Path(trial.result_path), result)