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/online_serving/ec_both_encoder/ec_both_encoder.sh

@@ -0,0 +1,73 @@
+#!/bin/bash
+set -euo pipefail
+
+MODEL="${MODEL:-Qwen/Qwen2.5-VL-3B-Instruct}"
+PORT="${PORT:-8000}"
+GPU="${GPU:-0}"
+NUM_PROMPTS="${NUM_PROMPTS:-200}"
+EC_SHARED_STORAGE_PATH="${EC_SHARED_STORAGE_PATH:-/tmp/ec_cache}"
+TIMEOUT="${TIMEOUT:-600}"
+
+SERVER_PID=""
+
+cleanup() {
+    echo "Stopping server..."
+    if [[ -n "$SERVER_PID" ]] && kill -0 "$SERVER_PID" 2>/dev/null; then
+        kill "$SERVER_PID" 2>/dev/null || true
+        wait "$SERVER_PID" 2>/dev/null || true
+    fi
+    echo "Done."
+}
+trap cleanup EXIT INT TERM
+
+wait_for_server() {
+    local deadline=$((SECONDS + TIMEOUT))
+    echo "Waiting for server on port $PORT..."
+    while (( SECONDS < deadline )); do
+        if curl -sf "http://localhost:${PORT}/v1/models" > /dev/null 2>&1; then
+            echo "Server ready."
+            return 0
+        fi
+        sleep 2
+    done
+    echo "ERROR: Server did not start within ${TIMEOUT}s"
+    return 1
+}
+
+rm -rf "$EC_SHARED_STORAGE_PATH"
+mkdir -p "$EC_SHARED_STORAGE_PATH"
+
+###############################################################################
+# Start server with ec_both
+###############################################################################
+CUDA_VISIBLE_DEVICES="$GPU" \
+vllm serve "$MODEL" \
+    --port "$PORT" \
+    --enforce-eager \
+    --ec-transfer-config '{
+        "ec_connector": "ECExampleConnector",
+        "ec_role": "ec_both",
+        "ec_connector_extra_config": {
+            "shared_storage_path": "'"$EC_SHARED_STORAGE_PATH"'"
+        }
+    }' \
+    "$@" &
+
+SERVER_PID=$!
+wait_for_server
+
+###############################################################################
+# Benchmark -- dataset contains duplicate images, exercises cache hits
+###############################################################################
+echo "Running benchmark ($NUM_PROMPTS prompts)..."
+vllm bench serve \
+    --model "$MODEL" \
+    --backend openai-chat \
+    --endpoint /v1/chat/completions \
+    --dataset-name hf \
+    --dataset-path lmarena-ai/VisionArena-Chat \
+    --seed 0 \
+    --num-prompts "$NUM_PROMPTS" \
+    --port "$PORT"
+
+echo "Benchmark complete."