[Fix] Populate _hidden_params.model_id in batch terminal-state shortcut path

The terminal-state DB shortcut in retrieve_batch returned a LiteLLMBatch
with empty _hidden_params, causing the managed_files hook to skip encoding
output_file_id into a unified ID. This adds the same model_id extraction
from unified_batch_id that the non-terminal path already has.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

litellm/proxy/batches_endpoints/endpoints.py

@@ -412,6 +412,16 @@ async def retrieve_batch(  # noqa: PLR0915
             "cancelled",
             "expired",
         ]:
+            # Populate _hidden_params.model_id so managed_files hook can
+            # encode output_file_id / error_file_id into unified IDs.
+            if unified_batch_id:
+                response._hidden_params["unified_batch_id"] = unified_batch_id
+                model_id_from_batch = get_model_id_from_unified_batch_id(
+                    unified_batch_id
+                )
+                if model_id_from_batch:
+                    response._hidden_params["model_id"] = model_id_from_batch
+
             # Call hooks and return
             response = await proxy_logging_obj.post_call_success_hook(
                 data=data, user_api_key_dict=user_api_key_dict, response=response

tests/test_litellm/enterprise/proxy/test_batch_terminal_state_hidden_params.py

@@ -0,0 +1,101 @@
+"""
+Test that the terminal-state shortcut path in retrieve_batch populates
+_hidden_params.model_id from the unified batch ID.
+
+Regression: When a batch is in a terminal state (completed/failed/cancelled/expired),
+the DB shortcut path returned a LiteLLMBatch with empty _hidden_params, causing the
+managed_files hook to skip encoding output_file_id into a unified ID.
+"""
+
+import base64
+
+import pytest
+
+from litellm.proxy.openai_files_endpoints.common_utils import (
+    get_model_id_from_unified_batch_id,
+)
+from litellm.types.utils import LiteLLMBatch
+
+
+MODEL_ID = "model-xyz-123"
+RAW_BATCH_ID = "batch-provider-456"
+DECODED_UNIFIED_BATCH_ID = (
+    f"litellm_proxy;model_id:{MODEL_ID};llm_batch_id:{RAW_BATCH_ID}"
+)
+B64_UNIFIED_BATCH_ID = (
+    base64.urlsafe_b64encode(DECODED_UNIFIED_BATCH_ID.encode()).decode().rstrip("=")
+)
+
+
+def test_get_model_id_from_unified_batch_id():
+    """model_id is correctly extracted from a unified batch ID."""
+    assert get_model_id_from_unified_batch_id(DECODED_UNIFIED_BATCH_ID) == MODEL_ID
+
+
+def test_get_model_id_returns_none_for_invalid():
+    """Returns None for non-unified IDs."""
+    assert get_model_id_from_unified_batch_id("plain-batch-id") is None
+    assert get_model_id_from_unified_batch_id("") is None
+
+
+@pytest.mark.parametrize("status", ["completed", "failed", "cancelled", "expired"])
+def test_terminal_batch_hidden_params_population(status):
+    """
+    Simulate the terminal-state shortcut path logic: when a batch from the DB
+    has a terminal status and we have a unified_batch_id, _hidden_params should
+    get model_id and unified_batch_id set.
+
+    This mirrors the code added to endpoints.py lines 415-423.
+    """
+    # Create a batch as it would come from the database (empty _hidden_params)
+    response = LiteLLMBatch(
+        id=B64_UNIFIED_BATCH_ID,
+        completion_window="24h",
+        created_at=1700000000,
+        endpoint="/v1/chat/completions",
+        input_file_id="file-input-abc",
+        object="batch",
+        status=status,
+        output_file_id="file-output-raw",
+    )
+
+    assert response._hidden_params.get("model_id") is None, "precondition: no model_id"
+
+    unified_batch_id = DECODED_UNIFIED_BATCH_ID
+
+    # This is the exact logic from the terminal-state shortcut path
+    if unified_batch_id:
+        response._hidden_params["unified_batch_id"] = unified_batch_id
+        model_id_from_batch = get_model_id_from_unified_batch_id(unified_batch_id)
+        if model_id_from_batch:
+            response._hidden_params["model_id"] = model_id_from_batch
+
+    assert response._hidden_params["model_id"] == MODEL_ID
+    assert response._hidden_params["unified_batch_id"] == DECODED_UNIFIED_BATCH_ID
+
+
+def test_terminal_batch_no_unified_id_leaves_hidden_params_empty():
+    """
+    When there is no unified_batch_id (non-managed batch), _hidden_params
+    should remain unchanged.
+    """
+    response = LiteLLMBatch(
+        id="batch-plain-id",
+        completion_window="24h",
+        created_at=1700000000,
+        endpoint="/v1/chat/completions",
+        input_file_id="file-input-abc",
+        object="batch",
+        status="completed",
+    )
+
+    unified_batch_id = None
+
+    if unified_batch_id:
+        response._hidden_params["unified_batch_id"] = unified_batch_id
+        model_id_from_batch = get_model_id_from_unified_batch_id(unified_batch_id)
+        if model_id_from_batch:
+            response._hidden_params["model_id"] = model_id_from_batch
+
+    assert response._hidden_params.get("model_id") is None
+    assert response._hidden_params.get("unified_batch_id") is None