# Track Specification: Session Insights & Efficiency Scores (session_insights_20260306)

## Overview
Token usage over time, cost projections, session summary with efficiency scores. Visualize session_logger data.

## Architectural Constraints
- **Efficient Calculation**: Metrics MUST be calculated incrementally.
- **Real-Time**: Updates SHOULD reflect current session state.

## Functional Requirements
- **Token Timeline**: Graph of token usage over session.
- **Cost Projection**: Estimate remaining budget based on usage.
- **Efficiency Score**: Calculate tokens-per-useful-change ratio.
- **Session Summary**: Text summary of session metrics.

## Acceptance Criteria
- [ ] Token timeline renders.
- [ ] Cost projection accurate.
- [ ] Efficiency score calculated.
- [ ] Summary displays key metrics.
- [ ] Uses existing session_logger.