Struct C 

pub struct C;

The C namespace — static factory methods for context policies.

Implementations

impl C

pub fn window(n: usize) -> ContextPolicy

Keep only the last n messages.

pub fn user_only() -> ContextPolicy

Keep only messages with role “user”.

pub fn custom( f: impl Fn(&[Content]) -> Vec<Content> + Send + Sync + 'static, ) -> ContextPolicy

Apply a custom filter function.

pub fn model_only() -> ContextPolicy

Keep only messages with role “model”.

pub fn head(n: usize) -> ContextPolicy

Keep the first n messages (head).

pub fn sample(n: usize) -> ContextPolicy

Keep every n-th message (sampling).

pub fn exclude_tools() -> ContextPolicy

Exclude messages that contain tool-related parts (function calls/responses).

pub fn prepend(content: Content) -> ContextPolicy

Prepend a system message to the context.

pub fn append(content: Content) -> ContextPolicy

Append a content to the context.

pub fn text_only() -> ContextPolicy

Keep only messages that contain text parts.

pub fn filter( f: impl Fn(&Content) -> bool + Send + Sync + 'static, ) -> ContextPolicy

Filter messages by a predicate on Content.

pub fn map( f: impl Fn(&Content) -> Content + Send + Sync + 'static, ) -> ContextPolicy

Map/transform each message in the context.

pub fn truncate(max_chars: usize) -> ContextPolicy

Truncate context to approximately max_chars total characters of text.

pub fn empty() -> ContextPolicy

Return an empty context (useful for isolated agents).

pub fn from_state(keys: &[&str]) -> ContextPolicy

Inject state values as context preamble.

Bridges Channel 2 (State) → Channel 1 (Conversation History) by prepending formatted state values as a system context message.

Example

let policy = C::from_state(&["user:name", "app:account_balance", "derived:risk"]);
// Produces: "[Context: name=John, account_balance=$5230, risk=0.72]"

pub fn template(tpl: &str) -> ContextPolicy

Template-based context injection with {key} placeholders.

Replaces placeholders in the template with state key references.

pub fn when( predicate: impl Fn() -> bool + Send + Sync + 'static, inner: ContextPolicy, ) -> ContextPolicy

Conditional context — applies inner policy only when predicate is true.

Falls back to passing history through unchanged.

pub fn redact(patterns: &[&str]) -> ContextPolicy

Redact patterns from context messages.

pub fn summarize(prompt: &str) -> ContextPolicy

LLM-powered context summarization.

Stores a summarization prompt that the runtime uses to condense context via an LLM call before passing it to the agent. The policy prepends a marker so the runtime knows summarization is requested.

Example

let policy = C::summarize("Summarize the conversation focusing on action items");

pub fn relevant(query_key: &str) -> ContextPolicy

Keep only context relevant to a state key.

Marker policy for LLM-powered relevance filtering. The runtime uses the referenced state key’s value to filter context entries by relevance.

Example

let policy = C::relevant("user:current_topic");

pub fn extract(keys: &[&str]) -> ContextPolicy

Extract specific information from context.

Marker policy that signals the runtime to extract only the named pieces of information from the conversation history via an LLM call.

Example

let policy = C::extract(&["customer_name", "order_id", "complaint"]);

pub fn distill(instruction: &str) -> ContextPolicy

Distill context to essential information.

Marker policy for LLM-powered distillation. Similar to summarize but focused on extracting only the essential facts per the given instruction.

Example

let policy = C::distill("Keep only decisions made and their rationale");

pub fn priority(weights: &[(&str, f64)]) -> ContextPolicy

Priority-weighted context selection.

Assigns weights to context entries by role or content pattern. Higher weight entries are kept preferentially when context must be truncated. Weights are encoded as a marker for runtime processing.

Example

let policy = C::priority(&[("user", 1.0), ("model", 0.5), ("tool", 0.2)]);

pub fn fit(max_tokens: usize) -> ContextPolicy

Fit context to a token budget with smart truncation.

Similar to truncate (a character budget, ~4 chars per token) but adds a truncation marker so the runtime knows content was trimmed, allowing the agent to request more context if needed.

Example

let policy = C::fit(4096);

pub fn project(fields: &[&str]) -> ContextPolicy

Project/keep only specific fields from context.

Marker policy that signals the runtime to retain only the named fields from structured content in the conversation history.

Example

let policy = C::project(&["name", "status", "priority"]);

pub fn select( predicate: impl Fn(&Content) -> bool + Send + Sync + 'static, ) -> ContextPolicy

Select context entries matching a predicate.

Similar to filter but with select semantics: entries matching the predicate are included (positive selection).

pub fn from_agents(names: &[&str]) -> ContextPolicy

Include context only from specific agents.

Filters context to keep only messages attributed to the named agents. Agent attribution is detected via [Agent: name] markers in content.

Example

let policy = C::from_agents(&["researcher", "analyst"]);

pub fn exclude_agents(names: &[&str]) -> ContextPolicy

Exclude context from specific agents.

Filters out messages attributed to the named agents. Agent attribution is detected via [Agent: name] markers in content.

Example

let policy = C::exclude_agents(&["logger", "debugger"]);

pub fn notes(key: &str) -> ContextPolicy

Scratchpad: read notes from a state key as context.

Prepends the value of a state key as a notes/scratchpad section in the context. Useful for maintaining running notes across turns.

Example

let policy = C::notes("session:scratchpad");

pub fn pipeline_aware() -> ContextPolicy

Pipeline-aware context that adapts based on pipeline position.

Marker policy that signals the runtime to adjust context based on where the current agent sits in a pipeline. Early stages receive full context; later stages receive only the outputs of preceding stages.

Example

let policy = C::pipeline_aware();

pub fn dedup() -> ContextPolicy

Deduplicate adjacent messages with identical text content.