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/models/quantization/test_gpt_oss.py

@@ -0,0 +1,122 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""
+End-to-end accuracy test for GPT-OSS model quantization.
+
+Config:
+    Task:   gsm8k_platinum
+    Filter: flexible-extract
+    n-shot: 5
+    Metric: exact_match
+
+Run: pytest tests/models/quantization/test_gpt_oss.py
+"""
+
+import importlib.metadata
+import importlib.util
+from dataclasses import dataclass
+
+import huggingface_hub
+import lm_eval
+import pytest
+from packaging import version
+
+from vllm.platforms.rocm import on_gfx950
+from vllm.utils.torch_utils import cuda_device_count_stateless
+
+MODEL_ACCURACIES = {
+    # Full quantization: attention linears and MoE linears
+    "amd/gpt-oss-20b-WFP8-AFP8-KVFP8": 0.89,
+    # MoE linears only quantization
+    "amd/gpt-oss-20b-MoE-Quant-W-MXFP4-A-FP8-KV-FP8": 0.89,
+    # MoE linears only quantization
+    # "amd/gpt-oss-20b-MoE-Quant-W-MXFP4-A-MXFP4-KV-FP8": 0.90,
+}
+
+QUARK_MXFP4_AVAILABLE = importlib.util.find_spec("quark") is not None and version.parse(
+    importlib.metadata.version("amd-quark")
+) >= version.parse("0.9.0")
+
+
+def has_huggingface_access(repo):
+    try:
+        huggingface_hub.list_repo_refs(repo)
+        return True
+    except huggingface_hub.errors.RepositoryNotFoundError:
+        return False
+
+
+HF_HUB_AMD_ORG_ACCESS = all(
+    [has_huggingface_access(model_name) for model_name in MODEL_ACCURACIES]
+)
+
+
+@dataclass
+class ModelCase:
+    model_id: str
+    tp: int
+
+
+@dataclass
+class EvaluationConfig:
+    model_name: str
+
+    def get_model_args(self, tp_size: int):
+        return {
+            "pretrained": self.model_name,
+            "chat_template_args": {"reasoning_effort": "low"},
+            "enable_thinking": True,
+            "think_end_token": "200008",
+            "tensor_parallel_size": tp_size,
+            "dtype": "auto",
+            "gpu_memory_utilization": 0.95,
+            "trust_remote_code": False,
+            "enable_prefix_caching": False,
+            "enforce_eager": False,
+        }
+
+
+@pytest.mark.skipif(not QUARK_MXFP4_AVAILABLE, reason="amd-quark>=0.9 is not available")
+@pytest.mark.skipif(
+    not HF_HUB_AMD_ORG_ACCESS,
+    reason="Read access to huggingface.co/amd is required for this test.",
+)
+@pytest.mark.parametrize("tp_size", [1, 2, 4, 8])
+@pytest.mark.parametrize("model_name, expected_accuracy", MODEL_ACCURACIES.items())
+def test_gpt_oss_attention_quantization(
+    model_name: str,
+    tp_size: int,
+    expected_accuracy: float,
+    monkeypatch: pytest.MonkeyPatch,
+):
+    if tp_size > cuda_device_count_stateless():
+        pytest.skip("Not enough GPUs to run this test case")
+
+    if "amd/gpt-oss-20b-MoE-Quant-W-MXFP4-A-FP8-KV-FP8" in model_name and on_gfx950():
+        monkeypatch.setenv("VLLM_ROCM_USE_AITER", "1")
+
+    model_args = EvaluationConfig(model_name).get_model_args(tp_size)
+
+    extra_run_kwargs = {
+        "gen_kwargs": {"max_gen_toks": 8000},
+        "apply_chat_template": True,
+        "fewshot_as_multiturn": True,
+        "num_fewshot": 5,
+    }
+
+    lm_eval_out = lm_eval.simple_evaluate(
+        model="vllm",
+        model_args=model_args,
+        tasks="gsm8k_platinum",
+        batch_size="auto",
+        **extra_run_kwargs,
+    )
+    measured_accuracy = float(
+        lm_eval_out["results"]["gsm8k_platinum"]["exact_match,flexible-extract"]
+    )
+
+    rtol = 0.02
+    assert measured_accuracy >= expected_accuracy - rtol, (
+        f"Accuracy {measured_accuracy:.4f} is below threshold "
+        f"{expected_accuracy - rtol:.4f} (expected >= {expected_accuracy} - {rtol})"
+    )