Struct CostTracker 

pub struct CostTracker { /* private fields */ }

Tracks token usage and cost across an agent run, persisting to the session directory.

CostTracker is designed to be used alongside SessionWriter. It writes a cost.json file into the same session directory and optionally updates the .meta.json file with cost summary fields.

Implementations

impl CostTracker

pub fn new(session_dir: PathBuf, model: &str, provider: &str) -> Self

Create a new CostTracker for the given session directory.

session_dir should be the same directory used by SessionWriter. Pricing is looked up from the bundled providers.toml via pricing_for().

pub fn record_usage(&mut self, usage: TokenUsage, latency_ms: u64)

Record token usage and latency from a single LLM call.

Call this from the integration layer after each runtime.run(), passing outcome.total_usage and outcome.llm_latency_ms from the RuntimeOutcome.

pub fn accumulated_usage(&self) -> TokenUsage

Return the accumulated token usage so far.

pub fn accumulated_latency_ms(&self) -> u64

Return the accumulated LLM latency in milliseconds.

pub fn cost_usd(&self) -> Option<f64>

Compute the cost in USD for the accumulated usage.

Returns None if pricing is unknown for the model.

pub fn cost_data(&self) -> CostData

Build the current CostData snapshot.

pub fn write_cost_json(&self) -> Result<PathBuf>

Write the cost data to cost.json in the session directory.

Returns the path to the written file.

pub fn update_meta_with_cost(&self) -> Result<()>

Update the .meta.json file in the session directory with cost summary fields.

Reads the existing meta file, adds cost fields, and writes it back. If the meta file doesn’t exist or can’t be read, this is a no-op.

pub fn finish(&mut self) -> Result<()>

Finalise the tracker: write cost.json and update .meta.json.

After calling this, the tracker is marked as finished and subsequent calls are no-ops.