fix(litellm): retry transient upstream 5xx at the proxy

src/benchflow/providers/litellm_config.py

@@ -425,6 +425,14 @@ def litellm_proxy_config(
             # storms or deployment cooldown fast-fails (#830).
             "num_retries": 0,
             "disable_cooldowns": True,
+            # ...with ONE narrow exception honoring #830's rationale: transient
+            # upstream 5xx (InternalServerError) are not deterministic rejects,
+            # and some agents silently swallow a passed-through 500 into a
+            # zero-event turn (observed: MiMo Code ending turns with no error on
+            # a deepseek 500, repro x3). Absorb up to 2 transient 500s at the
+            # proxy; every deterministic class (4xx, auth, content) still fails
+            # fast with zero retries.
+            "retry_policy": {"InternalServerErrorRetries": 2},
         },
         "litellm_settings": {
             "callbacks": [f"{callback_module}.proxy_handler_instance"],

tests/test_litellm_config.py

@@ -181,6 +181,10 @@ def test_proxy_config_registers_plain_and_openai_aliases():
     assert config["router_settings"] == {
         "num_retries": 0,
         "disable_cooldowns": True,
+        # transient-5xx-only exception to the no-retry rule (#830 honored:
+        # deterministic classes keep zero retries) — absorbs upstream 500s that
+        # some agents (MiMo) silently swallow into zero-event turns.
+        "retry_policy": {"InternalServerErrorRetries": 2},
     }