Fixes #15247 | Update chat.cpp to support (at least) qwen3 reasoning + tool_choice = required

[ExtReMLapin]

There was this issue that we would not use tool_choice at required with reasoning because of forced tool call imposed by grammar.

Grammar now allows the model to think first.

Reasoning = big brain

Tool calling = strong arms

Now you can be very smart and very strong

Fixes #15247

[ExtReMLapin]

All am I sure is that it fixes issues with Qwen3 + reasoning (enabled or disabled)+ tool calling.
I fear it also has to be implemented for others reasoning parsers (non hermes)

CC hermes2 contributor : @ochafik

[ExtReMLapin]

Back at the office on tuesday, re-reading the PR i might reconsider the logic around

thinking_forced_open

[ExtReMLapin]

For a future PR, the following functions needs the same kind of patch :

• common_chat_params_init_granite : same as qwen3, but i'm not sure as the thinking tags are not always there
• common_chat_params_init_command_r7b : "<|START_THINKING|>", "<|END_THINKING|>"
• common_chat_params_init_deepseek_r1 : same as qwen3
• common_chat_params_init_gpt_oss ???

ready for review @ggerganov

Not sure exactly who I should ping as ochafik seems to be busy this week

[ExtReMLapin]

Not sure who I should ping

@slaren

[ggerganov]

Same comment as #15019 (comment)

This is a smaller change, so I can take a look and merge this, but prefer if we have someone who would take over this part of the code.

[ExtReMLapin]

Got it, thanks for keeping me updated !