[KV Connector] Add temporary, off-by-default VLLM_DISABLE_REQUEST_ID_RANDOMIZATION workaround (#34415)

Signed-off-by: Seiji Eicher <seiji@anyscale.com>

vllm/v1/engine/input_processor.py

@@ -5,6 +5,7 @@ import time
 from collections.abc import Mapping
 from typing import Any, Literal, cast
 
+import vllm.envs as envs
 from vllm.config import VllmConfig
 from vllm.inputs.data import (
     ProcessorInputs,
@@ -296,7 +297,14 @@ class InputProcessor:
                 " passed to vLLM; use the request_id field."
             )
         request.external_req_id = request.request_id
-        request.request_id = f"{request.external_req_id}-{random_uuid():.8}"
+        if envs.VLLM_DISABLE_REQUEST_ID_RANDOMIZATION:
+            logger.warning_once(
+                "VLLM_DISABLE_REQUEST_ID_RANDOMIZATION is set and will be "
+                "removed in a future release. Duplicate externally-provided "
+                "request IDs may cause failures and/or subtle correctness errors."
+            )
+        else:
+            request.request_id = f"{request.external_req_id}-{random_uuid():.8}"
 
     def process_inputs(
         self,