chore(vertex-batches): wrap api_base GET in safe_get for defense-in-depth

The vertex batches status-poll fetches an attacker-influenceable
``api_base`` URL with a raw ``sync_handler.get()``. The proxy auth gate
already validates clientside ``api_base`` before reaching this sink, so
the proxy flow is covered. This adds the per-sink wrap so SDK callers
and any future code path that bypasses the proxy gate pick up the same
SSRF defense from ``url_utils.safe_get``.

Operators with a legitimate private Vertex base can either allowlist
the host via ``litellm.user_url_allowed_hosts`` or disable validation
with ``litellm.user_url_validation = False``.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

litellm/llms/vertex_ai/batches/handler.py

@@ -4,6 +4,7 @@ from typing import Any, Coroutine, Dict, Optional, Union
 import httpx
 
 import litellm
+from litellm.litellm_core_utils.url_utils import safe_get
 from litellm.llms.custom_httpx.http_handler import (
     _get_httpx_client,
     get_async_httpx_client,
@@ -224,8 +225,14 @@ class VertexAIBatchPrediction(VertexLLM):
                     },
                 )
 
-        response = sync_handler.get(
-            url=api_base,
+        # ``api_base`` here can come from caller-supplied request kwargs
+        # (clientside override). Wrap the fetch in ``safe_get`` so DNS
+        # rebind / private / cloud-metadata targets are rejected; the
+        # proxy auth gate already blocks malicious clientside ``api_base``
+        # at the boundary — this is defense-in-depth for SDK callers.
+        response = safe_get(
+            sync_handler,
+            api_base,
             headers=headers,
         )