Struct ContextWindow 

pub struct ContextWindow<M: BaseChatModel> { /* private fields */ }

Context window manager for fitting messages within a token budget.

Counts tokens using a TokenCounter (defaults to TiktokenCounter), and applies a Strategy when messages exceed max_tokens.

Implementations

impl<M: BaseChatModel> ContextWindow<M>

pub fn new(max_tokens: usize) -> Result<Self, MemoryError>

Creates a new ContextWindow with the Truncate strategy and default TiktokenCounter.

P1-4: 返回 Result 而非 panic——tiktoken 模型下载/加载失败(离线/缺模型) 时返回 MemoryError,库构造器不再因本地环境崩溃。

pub fn with_strategy( max_tokens: usize, strategy: Strategy<M>, ) -> Result<Self, MemoryError>

Creates a new ContextWindow with a specific strategy and default TiktokenCounter.

pub fn with_max_tokens(max_tokens: usize) -> Result<Self, MemoryError>

Creates a new ContextWindow with a custom max token limit and default counter/strategy.

pub fn with_counter(self, counter: Arc<dyn TokenCounter>) -> Self

Sets a custom token counter.

pub fn max_tokens(&self) -> usize

Returns the max token limit.

pub async fn fit( &self, messages: Vec<Message>, ) -> Result<Vec<Message>, MemoryError>

Fits messages within the token limit by applying the configured strategy.

• If total tokens are within max_tokens, returns messages as-is.
• If over, applies the Strategy (truncate or summarize).

Budget semantics (P1-4 契约)

Strategy::Truncate: System 消息恒保留且不占预算;若 System 消息 自身超过 max_tokens,原样返回(结果可能超预算)。调用方不应假设 fit 的返回结果一定在预算内。

Strategy::Summarize: 摘要占位计入预算,但 LLM 实际产出的摘要 token 数未知——预算语义与 Truncate 不同,两者在 System 消息上口径不一致是有意为之, 各策略自行定义。

Arguments

• messages - The conversation messages to fit.

Returns

A vector of messages that fits within the token budget.