pi sends tool_choice="auto" for every session (Read/Bash/etc.) -- vLLM 400s on that without --enable-auto-tool-choice and a --tool-call-parser. Verified this deployed vLLM v0.11.0's registered parsers directly; deepseek_v3 matches, same family as the deepseek_r1 reasoning-parser already set (this Qwen-base distillation still emits DeepSeek's own tool-call format).