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/docs/features/mooncake_connector_usage.md

@@ -0,0 +1,69 @@
+# MooncakeConnector Usage Guide
+
+## About Mooncake
+
+Mooncake aims to enhance the inference efficiency of large language models (LLMs), especially in slow object storage environments, by constructing a multi-level caching pool on high-speed interconnected DRAM/SSD resources. Compared to traditional caching systems, Mooncake utilizes (GPUDirect) RDMA technology to transfer data directly in a zero-copy manner, while maximizing the use of multi-NIC resources on a single machine.
+
+For more details about Mooncake, please refer to [Mooncake project](https://github.com/kvcache-ai/Mooncake) and [Mooncake documents](https://kvcache-ai.github.io/Mooncake/).
+
+## Prerequisites
+
+### Installation
+
+Install mooncake through pip: `uv pip install mooncake-transfer-engine`.
+
+Refer to [Mooncake official repository](https://github.com/kvcache-ai/Mooncake) for more installation instructions
+
+## Usage
+
+### Prefiller Node (192.168.0.2)
+
+```bash
+vllm serve Qwen/Qwen2.5-7B-Instruct --port 8010 --kv-transfer-config '{"kv_connector":"MooncakeConnector","kv_role":"kv_producer"}'
+```
+
+### Decoder Node (192.168.0.3)
+
+```bash
+vllm serve Qwen/Qwen2.5-7B-Instruct --port 8020 --kv-transfer-config '{"kv_connector":"MooncakeConnector","kv_role":"kv_consumer"}'
+```
+
+### Proxy
+
+```bash
+python examples/online_serving/disaggregated_serving/mooncake_connector/mooncake_connector_proxy.py --prefill http://192.168.0.2:8010 --decode http://192.168.0.3:8020
+```
+
+Now you can send requests to the proxy server through port 8000.
+
+## Environment Variables
+
+- `VLLM_MOONCAKE_BOOTSTRAP_PORT`: Port for Mooncake bootstrap server
+    - Default: 8998
+    - Required only for prefiller instances
+    - For headless instances, must be the same as the master instance
+    - Each instance needs a unique port on its host; using the same port number across different hosts is fine
+
+- `VLLM_MOONCAKE_ABORT_REQUEST_TIMEOUT`: Timeout (in seconds) for automatically releasing the prefiller’s KV cache for a particular request. (Optional)
+    - Default: 480
+    - If a request is aborted and the decoder has not yet notified the prefiller, the prefill instance will release its KV-cache blocks after this timeout to avoid holding them indefinitely.
+
+## KV Transfer Config
+
+### KV Role Options
+
+- **kv_producer**: For prefiller instances that generate KV caches
+- **kv_consumer**: For decoder instances that consume KV caches from prefiller
+- **kv_both**: Enables symmetric functionality where the connector can act as both producer and consumer. This provides flexibility for experimental setups and scenarios where the role distinction is not predetermined.
+
+### kv_connector_extra_config
+
+- **num_workers**: Size of thread pool for one prefiller worker to transfer KV caches by mooncake. (default 10)
+- **mooncake_protocol**: Mooncake connector protocol. (default "rdma")
+
+## Example Scripts/Code
+
+Refer to these example scripts in the vLLM repository:
+
+- [run_mooncake_connector.sh](../../examples/online_serving/disaggregated_serving/mooncake_connector/run_mooncake_connector.sh)
+- [mooncake_connector_proxy.py](../../examples/online_serving/disaggregated_serving/mooncake_connector/mooncake_connector_proxy.py)