fix(router): leave out the no-fallback note when a create stops after an order fallback

A create that fails at a later order level after an earlier level fell back now ends without
the "No fallback was attempted" note, since a fallback did run. The proxy's notice that the
provider may already hold the file or batch still comes through

litellm/router_rust/core.py

@@ -4421,6 +4421,7 @@ class _Driver:
         # The primary level reached the end of `async_function_with_fallbacks_common_utils`, the
         # only place the outcome message is appended: not its early raises, nor its order path.
         self._explains_failure: bool = False
+        self._order_chain_ran: bool = False
 
     def _blocked(self, response: object, endpoint_name: str) -> str | None:
         """How the provider blocked a served response, the first check of
@@ -4621,6 +4622,7 @@ class _Driver:
             self._level_errors[at] = last_hop
         if at == self._base_level:
             self._explains_failure = False
+            self._order_chain_ran = True
 
     def _logged_off_the_loop(self) -> bool:
         """Whether litellm logged the attempt's failure on a thread with no running loop. An async
@@ -5445,7 +5447,10 @@ class _Driver:
             )
         if (
             self._base_level == 0
-            and (self._explains_failure or self._is_create_that_may_already_exist(primary))
+            and (
+                self._explains_failure
+                or (not self._order_chain_ran and self._is_create_that_may_already_exist(primary))
+            )
             and self._core._host.dynamic().expose_router_debug_in_errors  # pyright: ignore[reportPrivateUsage]  # see above
             and hasattr(primary, "message")
         ):

tests/unit/test_router/test_router_retries.py

@@ -923,10 +923,11 @@ async def test_a_create_that_times_out_on_a_fallback_is_not_sent_to_the_next_fal
         )
     )
 
-    with pytest.raises(openai.APITimeoutError):
+    with pytest.raises(openai.APITimeoutError) as raised:
         await _create(_batch_router(api_bases, num_retries=0), create)
 
     assert [route.call_count for route in routes] == [1, 1, 0]
+    assert "No fallback was attempted" not in raised.value.message
 
 
 @pytest.mark.parametrize("unsent_timeout", [httpx.ConnectTimeout, httpx.PoolTimeout])