Struct Turn 

pub struct Turn {
    pub role: String,
    pub content: String,
    pub tool_calls: Vec<ToolCall>,
    pub reasoning: Option<String>,
    pub tool_call_id: Option<String>,
    pub tool_name: Option<String>,
    pub tool_responses: Vec<(String, Val)>,
    pub task: Option<String>,
    pub tools: Vec<Val>,
}

One chat turn for the tools-capable renderer (apply_chat_template_tools). The reasoning/tool_call_id/tool_name/tool_responses fields are read ONLY by the gemma4 arm; the qwen/step arms use role/content/tool_calls and leave the rest default.

Fields

role: String

content: String

tool_calls: Vec<ToolCall>

reasoning: Option<String>

gemma4: assistant reasoning re-rendered as a <|channel>thought span (only for a tool_calls-carrying assistant after the last user message — the template’s guard).

tool_call_id: Option<String>

gemma4: on a role:“tool” turn, the OpenAI tool_call_id used to resolve the response name against the preceding assistant’s tool_calls[].id.

tool_name: Option<String>

gemma4: on a role:“tool” turn, the message’s own name field (fallback when the id does not resolve).

tool_responses: Vec<(String, Val)>

gemma4 native (Google) responses embedded on an assistant turn: (name, response value). OpenAI histories leave this empty and use role:“tool” turns instead.

task: Option<String>

deepseek-v4 quick-instruction task token (action/query/authority/domain/ title/read_url, encoding_dsv4 DS_TASK_SP_TOKENS). Set only by the dsv4 fixture harness (the internal-classification heads); the OpenAI serve surface has no task field, so every serve request leaves this None and every other dialect ignores it.

tools: Vec<Val>

deepseek-v4 per-turn tool function objects (encoding_dsv4 renders the tool declaration on the message carrying them — system on the serve surface, or a developer message in the search-pipeline fixtures). The serve path also passes request-level tools via tools_struct, which the dsv4 arm folds onto the leading system turn. Every other dialect ignores this.

Trait Implementations

impl Clone for Turn

fn clone(&self) -> Turn

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for Turn

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for Turn

fn default() -> Turn

Returns the “default value” for a type.

impl PartialEq for Turn

fn eq(&self, other: &Turn) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for Turn