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/entrypoints/openai/conftest.py

@@ -0,0 +1,51 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+import pytest
+
+from vllm.assets.audio import AudioAsset
+
+
+def add_attention_backend(server_args, attention_config):
+    """Append attention backend CLI arg if specified.
+
+    Args:
+        server_args: List of server arguments to extend in-place.
+        attention_config: Dict with 'backend' key, or None.
+    """
+    if attention_config and "backend" in attention_config:
+        server_args.extend(["--attention-backend", attention_config["backend"]])
+
+
+@pytest.fixture(scope="module")
+def rocm_aiter_fa_attention():
+    """Return attention config for transcription/translation tests on ROCm.
+
+    On ROCm, audio tests require ROCM_AITER_FA attention backend.
+    """
+    from vllm.platforms import current_platform
+
+    if current_platform.is_rocm():
+        return {"backend": "ROCM_AITER_FA"}
+    return None
+
+
+@pytest.fixture
+def mary_had_lamb():
+    path = AudioAsset("mary_had_lamb").get_local_path()
+    with open(str(path), "rb") as f:
+        yield f
+
+
+@pytest.fixture
+def winning_call():
+    path = AudioAsset("winning_call").get_local_path()
+    with open(str(path), "rb") as f:
+        yield f
+
+
+@pytest.fixture
+def foscolo():
+    # Test translation it->en
+    path = AudioAsset("azacinto_foscolo").get_local_path()
+    with open(str(path), "rb") as f:
+        yield f