prain: fix vLLM on ROCm (no CUDA capability families), smoke test and benchmark scripts

scripts/smoke.sh

@@ -0,0 +1,29 @@
+#!/bin/bash
+# Go/no-go: does this vLLM build run Gemma 4 on this GPU? Serves a 2-layer copy of MODEL_DIR with
+# random weights (port 8000, log in build/smoke.log), then sends a greedy request, the warm-up
+# shape (continue_final_message, priority) and the draft fields (vllm_xargs, cache_salt).
+# usage: scripts/smoke.sh MODEL_DIR [vllm serve args...]
+# Expected: READY, a JSON list of 3 (gibberish) strings, two {"id":"chatcmpl-... lines, STOPPED.
+# RDNA2 needs --attention-backend TRITON_ATTN: ROCM_ATTN's prefill kernel wants 160 KiB of LDS.
+cd "$(dirname "$0")/.." && . scripts/env.sh
+model=$1
+shift
+setsid vllm serve "$model" --served-model-name gemma4 --language-model-only --max-model-len 4096 \
+    --max-num-batched-tokens 1024 --max-num-seqs 2 --kv-cache-memory-bytes 805306368 --port 8000 \
+    --enforce-eager --moe-backend triton --scheduling-policy priority --load-format dummy \
+    --hf-overrides '{"text_config": {"num_hidden_layers": 2, "layer_types": ["sliding_attention", "full_attention"]}}' \
+    "$@" > build/smoke.log 2>&1 < /dev/null &
+server=$!
+for _ in $(seq 120); do
+    curl -sf localhost:8000/health > /dev/null && break
+    kill -0 $server 2> /dev/null || break
+    sleep 5
+done
+curl -sf localhost:8000/health > /dev/null && echo READY || { echo DIED; tail -40 build/smoke.log; exit 1; }
+python scripts/greedy.py http://127.0.0.1:8000 gemma4 | head -c 200; echo
+post() { curl -s localhost:8000/v1/chat/completions -H 'Content-Type: application/json' -d "$1" | head -c 60; echo; }
+post '{"model": "gemma4", "messages": [{"role": "user", "content": "Why is the sky"}], "max_tokens": 1, "add_generation_prompt": false, "continue_final_message": true, "priority": 1}'
+post '{"model": "gemma4", "messages": [{"role": "user", "content": "Hi"}], "max_tokens": 2, "vllm_xargs": {"prain": "draft"}, "cache_salt": "prain-draft"}'
+kill -INT -$server
+while curl -sf localhost:8000/health > /dev/null; do sleep 2; done
+echo STOPPED