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/examples/basic/online_serving/openai_chat_completion_client.py

@@ -0,0 +1,64 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Example Python client for OpenAI Chat Completion using vLLM API server
+NOTE: start a supported chat completion model server with `vllm serve`, e.g.
+    vllm serve meta-llama/Llama-2-7b-chat-hf
+"""
+
+import argparse
+
+from openai import OpenAI
+
+# Modify OpenAI's API key and API base to use vLLM's API server.
+openai_api_key = "EMPTY"
+openai_api_base = "http://localhost:8000/v1"
+
+messages = [
+    {"role": "system", "content": "You are a helpful assistant."},
+    {"role": "user", "content": "Who won the world series in 2020?"},
+    {
+        "role": "assistant",
+        "content": "The Los Angeles Dodgers won the World Series in 2020.",
+    },
+    {"role": "user", "content": "Where was it played?"},
+]
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(description="Client for vLLM API server")
+    parser.add_argument(
+        "--stream", action="store_true", help="Enable streaming response"
+    )
+    return parser.parse_args()
+
+
+def main(args):
+    client = OpenAI(
+        # defaults to os.environ.get("OPENAI_API_KEY")
+        api_key=openai_api_key,
+        base_url=openai_api_base,
+    )
+
+    models = client.models.list()
+    model = models.data[0].id
+
+    # Chat Completion API
+    chat_completion = client.chat.completions.create(
+        messages=messages,
+        model=model,
+        stream=args.stream,
+    )
+
+    print("-" * 50)
+    print("Chat completion results:")
+    if args.stream:
+        for c in chat_completion:
+            print(c)
+    else:
+        print(chat_completion)
+    print("-" * 50)
+
+
+if __name__ == "__main__":
+    args = parse_args()
+    main(args)

third_party/vllm/examples/basic/online_serving/openai_completion_client.py

@@ -0,0 +1,53 @@
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+
+import argparse
+
+from openai import OpenAI
+
+# Modify OpenAI's API key and API base to use vLLM's API server.
+openai_api_key = "EMPTY"
+openai_api_base = "http://localhost:8000/v1"
+
+
+def parse_args():
+    parser = argparse.ArgumentParser(description="Client for vLLM API server")
+    parser.add_argument(
+        "--stream", action="store_true", help="Enable streaming response"
+    )
+    return parser.parse_args()
+
+
+def main(args):
+    client = OpenAI(
+        # defaults to os.environ.get("OPENAI_API_KEY")
+        api_key=openai_api_key,
+        base_url=openai_api_base,
+    )
+
+    models = client.models.list()
+    model = models.data[0].id
+
+    # Completion API
+    completion = client.completions.create(
+        model=model,
+        prompt="A robot may not injure a human being",
+        echo=False,
+        n=2,
+        stream=args.stream,
+        logprobs=3,
+    )
+
+    print("-" * 50)
+    print("Completion results:")
+    if args.stream:
+        for c in completion:
+            print(c)
+    else:
+        print(completion)
+    print("-" * 50)
+
+
+if __name__ == "__main__":
+    args = parse_args()
+    main(args)