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 last(n: usize) -> ContextPolicy

Keep messages within a time window (by index offset from end). Alias for window — provided for API symmetry.

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

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

pub fn none() -> ContextPolicy

Alias for empty — matches upstream Python C.none().

pub fn recent(n: usize) -> ContextPolicy

Alias for window — matches upstream Python C.recent().

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 rolling(n: usize) -> ContextPolicy

Rolling window — keeps last N messages (alias with summarization hint).

pub fn compact() -> ContextPolicy

Compact context — removes tool call/response parts to reduce token usage.

pub fn budget(max_tokens: usize) -> ContextPolicy

Budget context — truncate to approximate token count.

Rough estimate: 4 chars per token.

pub fn fresh(max_entries: usize) -> ContextPolicy

Freshness filter — keep only messages within the last N entries.

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

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

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

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

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

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 budget but adds a truncation marker so the runtime knows content was trimmed, allowing the agent to request more context if needed.

Example

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

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

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

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

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

C::pipeline_aware()

pub fn dedup() -> ContextPolicy

Deduplicate adjacent messages with identical text content.