fix(router): handle InternalServerError in get_num_retries_from_retry_policy

RetryPolicy.InternalServerErrorRetries was accepted in config and
validated by pydantic but never read at runtime — the resolver had
branches for five error types and omitted InternalServerError. Operators
who configured per-error 5xx retries silently fell through to the
global num_retries default.

Added the missing isinstance branch and a regression test.

Fixes #37805

litellm/router_utils/get_retry_from_policy.py

@@ -8,6 +8,7 @@ from litellm.exceptions import (
     AuthenticationError,
     BadRequestError,
     ContentPolicyViolationError,
+    InternalServerError,
     RateLimitError,
     Timeout,
 )
@@ -26,6 +27,7 @@ def get_num_retries_from_retry_policy(
     TimeoutErrorRetries: Optional[int] = None
     RateLimitErrorRetries: Optional[int] = None
     ContentPolicyViolationErrorRetries: Optional[int] = None
+    InternalServerErrorRetries: Optional[int] = None
     """
     # if we can find the exception then in the retry policy -> return the number of retries
 
@@ -50,6 +52,8 @@ def get_num_retries_from_retry_policy(
         return retry_policy.ContentPolicyViolationErrorRetries
     if isinstance(exception, BadRequestError) and retry_policy.BadRequestErrorRetries is not None:
         return retry_policy.BadRequestErrorRetries
+    if isinstance(exception, InternalServerError) and retry_policy.InternalServerErrorRetries is not None:
+        return retry_policy.InternalServerErrorRetries
 
 
 def reset_retry_policy() -> RetryPolicy:

tests/router_unit_tests/test_router_helper_utils.py

@@ -1354,6 +1354,11 @@ def test_track_deployment_metrics(model_list):
             "ContentPolicyViolationError",
             7,
         ),
+        (
+            litellm.exceptions.InternalServerError,
+            "InternalServerError",
+            5,
+        ),
     ],
 )
 def test_get_num_retries_from_retry_policy(