fix(passthrough): tz guard, stale ref, async cleanup (greptile P2s on #30384)

Four P2 threads resolved:

1. **tz-aware vs tz-naive comparison can crash the stream**
   (`streaming_handler.py:51`). Wrapped the `true_start < start_time`
   comparison in try/except for `TypeError`. tzinfo mismatch now
   skips the override silently rather than propagating before the
   first chunk is yielded.
2. **Stale line-number reference** (`streaming_handler.py:68`). Dropped
   the `litellm_logging.py:1834-1837` pointer and rephrased the
   comment to describe the fallback semantically — no line number
   to rot.
3. **`_build_response_with_chunks` was `async` for no reason**
   (test_streaming_handler.py:37). Plain `def`, removed
   `asyncio.run(...)` wrapper at all four call sites.
4. **`captured_start_time["start_time"]` could raise `KeyError`
   instead of an informative assertion** if the logging task
   never executed. Added an explicit `assert "start_time" in ...`
   with a clear message before the value check, in both affected
   tests.

4/4 pass locally.

litellm/proxy/pass_through_endpoints/streaming_handler.py

@@ -43,11 +43,19 @@ class PassThroughStreamingHandler:
         # entered the proxy. Without this override, SpendLogs.startTime
         # is artificially deflated by the full TTFT, making
         # `endTime - startTime` shorter than reality.
+        # Guard the `<` comparison: a tz-aware vs tz-naive mix raises
+        # `TypeError: can't compare offset-naive and offset-aware datetimes`,
+        # which would propagate before the first chunk is yielded and
+        # break the whole stream.
         true_start = getattr(litellm_logging_obj, "start_time", None)
-        if isinstance(true_start, datetime) and (
-            not isinstance(start_time, datetime) or true_start < start_time
-        ):
-            start_time = true_start
+        if isinstance(true_start, datetime):
+            try:
+                if not isinstance(start_time, datetime) or true_start < start_time:
+                    start_time = true_start
+            except TypeError:
+                # tzinfo mismatch — skip the override rather than
+                # crashing the stream. The caller-supplied start_time stays.
+                pass
 
         raw_bytes: List[bytes] = []
         logging_scheduled = False

tests/test_litellm/proxy/pass_through_endpoints/test_streaming_handler.py

@@ -34,7 +34,7 @@ def _build_logging_obj(true_start: datetime, completion_start_time=None):
     return logging_obj
 
 
-async def _build_response_with_chunks(chunks):
+def _build_response_with_chunks(chunks):
     """Wrap a list of bytes chunks into an httpx.Response-shaped mock that
     yields them via aiter_bytes()."""
 
@@ -68,7 +68,7 @@ def test_chunk_processor_uses_logging_obj_start_time_when_earlier(monkeypatch):
 
     logging_obj = _build_logging_obj(true_start=earlier)
 
-    response = asyncio.run(_build_response_with_chunks([b"chunk-1", b"chunk-2"]))
+    response = _build_response_with_chunks([b"chunk-1", b"chunk-2"])
     captured_start_time = {}
 
     async def fake_log_streaming_request(*args, **kwargs):
@@ -91,6 +91,9 @@ def test_chunk_processor_uses_logging_obj_start_time_when_earlier(monkeypatch):
     )
     _drain(gen)
 
+    assert (
+        "start_time" in captured_start_time
+    ), "logging task never reached the route_streaming_logging_to_handler stub"
     assert captured_start_time["start_time"] == earlier, (
         "Handler must override the later caller-supplied start_time with the "
         "earlier logging-obj start_time."
@@ -106,7 +109,7 @@ def test_chunk_processor_keeps_caller_start_time_when_earlier(monkeypatch):
 
     logging_obj = _build_logging_obj(true_start=later)
 
-    response = asyncio.run(_build_response_with_chunks([b"chunk-1"]))
+    response = _build_response_with_chunks([b"chunk-1"])
     captured_start_time = {}
 
     async def fake_log_streaming_request(*args, **kwargs):
@@ -129,6 +132,9 @@ def test_chunk_processor_keeps_caller_start_time_when_earlier(monkeypatch):
     )
     _drain(gen)
 
+    assert (
+        "start_time" in captured_start_time
+    ), "logging task never reached the route_streaming_logging_to_handler stub"
     assert (
         captured_start_time["start_time"] == earlier
     ), "Caller-supplied start_time should win when it's already the earlier value."
@@ -143,7 +149,7 @@ def test_chunk_processor_records_completion_start_on_first_chunk(monkeypatch):
         completion_start_time=None,
     )
 
-    response = asyncio.run(_build_response_with_chunks([b"chunk-1", b"chunk-2"]))
+    response = _build_response_with_chunks([b"chunk-1", b"chunk-2"])
 
     monkeypatch.setattr(
         PassThroughStreamingHandler,
@@ -175,7 +181,7 @@ def test_chunk_processor_does_not_overwrite_existing_completion_start(monkeypatc
         completion_start_time=pre_set,
     )
 
-    response = asyncio.run(_build_response_with_chunks([b"chunk-1"]))
+    response = _build_response_with_chunks([b"chunk-1"])
 
     monkeypatch.setattr(
         PassThroughStreamingHandler,