Struct ContextBudget 

pub struct ContextBudget {
    pub window_size: usize,
}

Context budget configuration and enforcement.

Fields

window_size: usize

Maximum tokens in the context window.

Implementations

impl ContextBudget

pub fn new(window_size: usize) -> Self

Create a new context budget with the given window size.

pub fn estimate_tokens( &self, messages: &[Message], tools: &[ToolDefinition], ) -> usize

Estimate the token count of a set of messages and tool definitions.

Uses the chars/4 heuristic: each character is roughly 0.25 tokens. This is conservative (overestimates) which is safer than underestimating.

pub fn estimate_message_tokens(&self, messages: &[Message]) -> usize

Estimate tokens for messages only (no tool definitions).

pub fn per_result_cap(&self) -> usize

Maximum chars allowed per individual tool result.

pub fn single_result_max(&self) -> usize

Absolute maximum chars for a single tool result.

pub fn total_tool_headroom(&self) -> usize

Total chars available for all tool results combined.

pub fn truncate_result(text: &str, max_chars: usize) -> String

Truncate a tool result string to fit within max_chars.

If truncation occurs, appends a [truncated] marker.

pub fn apply_context_guard(&self, messages: &mut [Message]) -> bool

Apply the context guard to messages: trim oldest tool results when total tool result content exceeds headroom.

Returns the (possibly modified) messages and whether trimming occurred.

pub fn check_trim_needed( &self, messages: &[Message], tools: &[ToolDefinition], ) -> Option<TrimAction>

Determine the trim action needed based on current token estimate.

Returns None if no trimming needed, or the trim action to take.

pub fn apply_trim(&self, messages: &mut Vec<Message>, action: TrimAction)

Apply a trim action to messages. Returns the trimmed messages.

Preserves the first message (usually the user’s initial prompt) and system markers, then keeps the last N messages.

Trait Implementations

impl Clone for ContextBudget

fn clone(&self) -> ContextBudget

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ContextBudget

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

Formats the value using the given formatter.

impl Default for ContextBudget

fn default() -> Self

Returns the “default value” for a type.