Add vLLM v0.18.1 source tree with KV transfer abort fix

third_party/vllm/ now tracked in git for direct patch management.
Based on vLLM v0.18.1 release with one patch applied:

  vllm/v1/core/sched/scheduler.py:
    Replace fatal assert with graceful skip when KV transfer callback
    arrives for an already-aborted request during PD disaggregated serving.

Future vLLM modifications should be made directly in third_party/vllm/
and committed normally. The patches/ directory is kept as documentation
of what changed from upstream.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

third_party/vllm/tests/test_inputs.py

@@ -0,0 +1,31 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import pytest
+
+from vllm.config import ModelConfig, VllmConfig
+from vllm.inputs.preprocess import InputPreprocessor
+
+pytestmark = pytest.mark.cpu_test
+
+
+@pytest.mark.parametrize("model_id", ["facebook/chameleon-7b"])
+@pytest.mark.parametrize("prompt", ["", {"prompt_token_ids": []}])
+@pytest.mark.skip(
+    reason=(
+        "Applying huggingface processor on text inputs results in "
+        "significant performance regression for multimodal models. "
+        "See https://github.com/vllm-project/vllm/issues/26320"
+    )
+)
+def test_preprocessor_always_mm_code_path(model_id, prompt):
+    model_config = ModelConfig(model=model_id)
+    vllm_config = VllmConfig(model_config=model_config)
+    input_preprocessor = InputPreprocessor(vllm_config)
+
+    # HF processor adds sep token
+    tokenizer = input_preprocessor.get_tokenizer()
+    sep_token_id = tokenizer.vocab[tokenizer.sep_token]
+
+    processed_inputs = input_preprocessor.preprocess(prompt)
+    assert sep_token_id in processed_inputs["prompt_token_ids"]