fix: place Qwen tools before system prompt

[he-yufeng]

Summary

• render qwen3_5-style tool descriptions before user system content
• keep the old system-before-tools order for other tool formats
• add a regression test for the qwen3_5_nothink encode path

Fixes #10491.

To verify

• PYTHONPATH=src python -m pytest tests/data/test_template.py -k "qwen35_tools_precede_system_content" -q
• python -m py_compile src/llamafactory/data/template.py tests/data/test_template.py
• python -m ruff check src/llamafactory/data/template.py tests/data/test_template.py
• git diff --check

[gemini-code-assist]

Code Review

This pull request introduces a helper method _format_system_content to correctly order and format system instructions and tool definitions, specifically ensuring that tools precede system content for the qwen3_5 tool format. A corresponding unit test was also added to verify this behavior. The review feedback suggests improving the robustness of this new method by handling cases where the system argument might be None to prevent potential runtime TypeError during string concatenation.

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[gemini-code-assist]

To ensure robust defensive programming, _format_system_content should handle cases where system might be None (e.g., if self.default_system is not set or is set to None in custom templates). Accepting Optional[str] and defaulting to an empty string prevents potential runtime TypeError during string concatenation.

Suggested change

	def _format_system_content(self, system: str, tool_text: str) -> str:
	if tool_text and self.format_tools.tool_format == "qwen3_5":
	tool_text = tool_text.lstrip("\n")
	return tool_text + ("\n\n" + system if system else "")
	return system + tool_text
	def _format_system_content(self, system: Optional[str], tool_text: str) -> str:
	system = system or ""
	if tool_text and self.format_tools.tool_format == "qwen3_5":
	tool_text = tool_text.lstrip("\n")
	return tool_text + ("\n\n" + system if system else "")
	return system + tool_text