With `template.use_tokenizer_template: true` the sglang and vllm backends
render the prompt themselves via `tokenizer.apply_chat_template()`, and they
hand it plain string content. A chat template only emits the model's own media
tokens when the content is a list of parts, so the rendered prompt carries no
`<|vision_start|><|image_pad|><|vision_end|>`. The pixels do reach the engine
(`image_data` / `multi_modal_data`), but both engines locate them by scanning
the prompt for that token, so they are discarded silently: HTTP 200, no
warning, and the model answers as if no image had been attached.
Add `attach_media_parts()` to the shared `python_utils` helper and call it in
both backends: the last user turn is rebuilt as
`[{"type": "image"} * n, {"type": "video"} * n, {"type": "text", ...}]` before
templating, which makes the template emit the placeholders. The pixels keep
travelling out of band exactly as before.
Text-only requests are untouched - with no media the helper returns None and
the original string-content path runs unchanged. If a template cannot iterate
content parts (a text-only model), the parts render is caught and the request
falls back to the previous string-content prompt instead of failing.
Signed-off-by: Tai An <antai12232931@outlook.com>
Two bugs broke OpenAI-style tool calling on the MLX backend (and any
Python backend sharing backend/python/common), reproduced end-to-end on
LocalAI v4.5.5 with the metal-mlx backend and
mlx-community/Qwen3.5-2B-MLX-8bit.
messages_to_dicts left each tool call's function.arguments as the raw
OpenAI-wire JSON string. HuggingFace chat templates (e.g. Qwen3.5)
iterate arguments as a mapping (.items()), so any request whose history
contained a prior assistant tool_calls message failed with HTTP 500
"Generation failed: Can only get item pairs from a mapping." — breaking
every agent loop on its second turn. Decode the string back into a dict
so the template sees a mapping.
split_reasoning returned ("", text) whenever the opening think tag was
absent. Models like Qwen3.5 open the assistant turn already inside
thinking, so the generated text carries only the closing </think>; the
whole chain-of-thought leaked into content. When the opener is missing
but the closer is present, treat everything before the closer as
reasoning.
Adds platform-independent unit tests under backend/python/common
(stdlib-only, no MLX/venv required, following parent_watch_test.py).
Assisted-by: Claude Code:claude-opus-4-8
Co-authored-by: Ettore Di Giacinto <mudler@localai.io>
Tai An