The char-rp seat shipped with no tool-call parser at all, so every
tools-bearing request was rejected outright:
400 "auto" tool choice requires --enable-auto-tool-choice and
--tool-call-parser to be set
MeroMero-v2 is Gemma-4, which emits its own native
`<|tool_call>call:name{...}<tool_call|>` syntax rather than the
qwen3_coder XML the Qwen-family seats use. vLLM 0.24 ships a matching
`gemma4` parser whose TOOL_CALL_START/END, CHANNEL_START/END and escape
token constants line up with this tokenizer's etc/eoc/escape tokens
exactly.
Three flags, and they are a set:
- --tool-call-parser gemma4 + --enable-auto-tool-choice: the fix proper.
- --reasoning-parser gemma4: without it the post-tool-response turn
leaks a literal `<|channel>thought\n<channel|>` prefix into content
(upstream vllm #45834 — the chat template leaves the prompt inside an
open channel block).
- --default-chat-template-kwargs '{"enable_thinking": false}': MANDATORY
companion to the reasoning parser. The parser reads enable_thinking
from chat_template_kwargs and defaults it to True
(vllm/parser/gemma4.py:439); True makes is_reasoning_end() return
False at a new turn, pre-initialising the engine to REASONING, which
routes ALL plain RP prose into reasoning_content and returns a null
content — breaking every char-rp consumer. This template already
defaults enable_thinking to false (chat_template.jinja:350), so
passing it explicitly renders a byte-identical prompt (verified across
plain / tools / post-tool-response / system-prompt shapes). It changes
generation not at all; it only corrects the parser state machine.
Verified green on the live seat after deploy: tool call streaming and
non-streaming, tool-result round-trip (leak gone), plain prose in
content with reasoning null, vision unchanged.
vh