serve: enable OpenAI auto tool-calling (qwen3_xml) + reasoning split by default

A forum user hit HTTP 400 "'auto' tool choice requires --enable-auto-tool-choice
and --tool-call-parser to be set" — the server shipped without tool-calling
enabled, which is exactly what agent/tool workloads (the whole point) need.

- serve.sh + mtp_serve.sh now pass --enable-auto-tool-choice --tool-call-parser
  qwen3_xml --reasoning-parser qwen3 by default (overridable/disable via
  TOOL_PARSER= / REASONING_PARSER=).
- Parser matters: Qwen3.5 emits the XML tool format
  (<function=name><parameter=k>v</parameter></function>), so hermes returns 200
  but with EMPTY tool_calls (the call lands in content). qwen3_xml parses it.
  Verified on the box: tool_choice=auto -> tool_calls=[get_weather {city:Paris}];
  plain chat unaffected; <think> -> reasoning_content.
- README: document tool-calling defaults + that the server binds 0.0.0.0
  (LAN-reachable at http://<spark-ip>:8000; no auth).

runtime/mtp_serve.sh

@@ -15,6 +15,12 @@ LOAD_FORMAT="${LOAD_FORMAT:-fastsafetensors}"
 PORT="${PORT:-8000}"
 # Reclaim the CUDA-graph memory over-estimate to KV (see serve.sh). Set =1 to restore.
 export VLLM_MEMORY_PROFILER_ESTIMATE_CUDAGRAPHS="${VLLM_MEMORY_PROFILER_ESTIMATE_CUDAGRAPHS:-0}"
+# Auto tool-calling + reasoning split (see serve.sh). Off via TOOL_PARSER="" etc.
+TOOL_PARSER="${TOOL_PARSER:-qwen3_xml}"
+REASONING_PARSER="${REASONING_PARSER:-qwen3}"
+TOOL_ARG=()
+[ -n "$TOOL_PARSER" ] && TOOL_ARG+=(--enable-auto-tool-choice --tool-call-parser "$TOOL_PARSER")
+[ -n "$REASONING_PARSER" ] && TOOL_ARG+=(--reasoning-parser "$REASONING_PARSER")
 echo "[mtp] qwen3_5_mtp — backend=$BACKEND, num_speculative_tokens=$NSPEC, model=$MODEL"
 exec vllm serve "$MODEL" \
   --served-model-name qwen \
@@ -28,4 +34,5 @@ exec vllm serve "$MODEL" \
   --trust-remote-code \
   --load-format "$LOAD_FORMAT" \
   --attention-backend "$BACKEND" \
+  "${TOOL_ARG[@]}" \
   --speculative-config "{\"method\":\"qwen3_5_mtp\",\"num_speculative_tokens\":$NSPEC,\"model\":\"$MODEL\"}"

runtime/serve.sh

@@ -60,6 +60,22 @@ else
 fi
 python3 /host/patch_unify2.py || { [ "$NSPEC" = "0" ] && true; }
 
+# OpenAI automatic tool-calling + reasoning split. Without --enable-auto-tool-choice
+# + --tool-call-parser, any client that sends `tools` with tool_choice="auto" gets
+# HTTP 400 — so agent/tool workloads (the whole point here) need these on. The tool
+# parser only activates when a request carries `tools`, so leaving it on is free for
+# plain chat. Qwen3.5 emits the XML tool format
+# (<tool_call><function=name><parameter=k>v</parameter></function></tool_call>) -> the
+# qwen3_xml parser (NOT hermes, which only reads the JSON format -> empty tool_calls),
+# and <think> reasoning the qwen3 parser splits into `reasoning_content`. Verified:
+# tool_choice="auto" -> tool_calls=[get_weather {"city":"Paris"}]. Disable either with
+# TOOL_PARSER="" / REASONING_PARSER="", or override the name (e.g. qwen3_coder).
+TOOL_PARSER="${TOOL_PARSER:-qwen3_xml}"
+REASONING_PARSER="${REASONING_PARSER:-qwen3}"
+TOOL_ARG=()
+[ -n "$TOOL_PARSER" ] && TOOL_ARG+=(--enable-auto-tool-choice --tool-call-parser "$TOOL_PARSER")
+[ -n "$REASONING_PARSER" ] && TOOL_ARG+=(--reasoning-parser "$REASONING_PARSER")
+
 exec vllm serve "$MODEL" \
   --served-model-name qwen \
   --host 0.0.0.0 --port "$PORT" \
@@ -72,4 +88,5 @@ exec vllm serve "$MODEL" \
   --trust-remote-code \
   --load-format "$LOAD_FORMAT" \
   --attention-backend "$BACKEND" \
+  "${TOOL_ARG[@]}" \
   "${SPEC_ARG[@]}"