documents/CHANGELOG.md

# Changelog

All changes to the Invoice Exception Handler environment are recorded here.

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## [1.0.0] — 2025-01-20

### Added
- Initial implementation of InvoiceExceptionEnv with full OpenEnv API
- Three tasks: task1_price_variance, task2_duplicate_tax, task3_compound_fraud
- Pydantic v2 typed models for all environment objects
- FastAPI HTTP endpoints for HF Spaces validation
- Gradio UI for interactive exploration
- inference.py using OpenAI client with [START][STEP][END] log format
- openenv.yaml spec file
- Dockerfile for HF Spaces deployment

### Design decisions
- Used pure Python simulation (no external databases) for portability and determinism
- Compound fraud task has four signals to prevent simple greedy agents from scoring well
- Channel selection in Task 3 (phone vs email) tests policy knowledge, not just anomaly detection
- Grader uses sub-scores to allow partial credit for partial solutions