Microbench: prefill-decode interference + PD transfer lifecycle

Two microbenchmarks quantifying the elastic offload decision:

1. Interference (corrected): cold prefill causes 14-214x TPOT p90
   degradation on same-worker decode (D∈{1,2,4,8} × P∈{2k,8k,16k,32k}).
   Earlier run had a prefix-cache bug (deterministic prompts hit cache
   after rep 0); fixed with uuid+time_ns unique prompts.

2. Transfer lifecycle: PD-sep TTFT breakdown via Mooncake proxy,
   measuring prefill→RDMA→decode startup overhead.

Key finding: offload wins at all P≥2048 operating points —
transfer cost is 25-50% of interference cost even with bulk Mooncake.

microbench/interference/launch_vllm.sh

@@ -0,0 +1,57 @@
+#!/bin/bash
+# Launch a single vLLM instance on GPU 0 for interference microbenchmark.
+# Uses TP=1, enable-chunked-prefill, enable-prefix-caching.
+#
+# Usage: bash launch_microbench1.sh [chunk_size] [port]
+#   chunk_size: max_num_batched_tokens (default: 8192)
+#   port: serving port (default: 8000)
+
+set -euo pipefail
+
+CHUNK_SIZE=${1:-8192}
+PORT=${2:-8000}
+MODEL="${MODEL:-$HOME/models/Qwen/Qwen3-Coder-30B-A3B-Instruct}"
+GPU_ID=${GPU_ID:-0}
+LOG_FILE="vllm_microbench1_chunk${CHUNK_SIZE}.log"
+
+echo "=== Interference Microbench vLLM Instance ==="
+echo "Model: $MODEL"
+echo "GPU: $GPU_ID"
+echo "Port: $PORT"
+echo "Chunk size (max_num_batched_tokens): $CHUNK_SIZE"
+echo "Log: $LOG_FILE"
+echo ""
+
+# Kill any existing vLLM on this port
+pkill -f "vllm.*--port $PORT" 2>/dev/null || true
+sleep 2
+
+CUDA_VISIBLE_DEVICES=$GPU_ID python -m vllm.entrypoints.openai.api_server \
+    --model "$MODEL" \
+    --tensor-parallel-size 1 \
+    --enable-prefix-caching \
+    --dtype auto \
+    --gpu-memory-utilization 0.9 \
+    --max-model-len 200000 \
+    --max-num-batched-tokens "$CHUNK_SIZE" \
+    --port "$PORT" \
+    --trust-remote-code \
+    --disable-log-requests \
+    2>&1 | tee "$LOG_FILE" &
+
+VLLM_PID=$!
+echo "vLLM PID: $VLLM_PID"
+echo "$VLLM_PID" > .vllm_microbench1.pid
+
+# Wait for server to be ready
+echo "Waiting for server to start..."
+for i in $(seq 1 120); do
+    if curl -s "http://127.0.0.1:$PORT/v1/models" > /dev/null 2>&1; then
+        echo "Server ready after ${i}s!"
+        exit 0
+    fi
+    sleep 1
+done
+
+echo "ERROR: Server did not start within 120s"
+exit 1