id: DATA-DB-001
title: Databento Historical Price Source
status: backlog
priority: high
dependencies: []
estimated_effort: 2-3 days
created: 2026-03-28
updated: 2026-03-28

description: |
  Integrate Databento historical API as a data source for backtesting and scenario
  comparison pages. This replaces yfinance for historical data on backtest pages
  and provides reliable, high-quality market data.

acceptance_criteria:
  - DatabentoHistoricalPriceSource implements HistoricalPriceSource protocol
  - Cache layer prevents redundant downloads when parameters unchanged
  - Environment variable DATABENTO_API_KEY used for authentication
  - Cost estimation available before data fetch
  - GLD symbol resolved to XNAS.BASIC dataset
  - GC=F symbol resolved to GLBX.MDP3 dataset
  - Unit tests with mocked Databento responses pass

implementation_notes: |
  Key files:
  - app/services/backtesting/databento_source.py (new)
  - tests/test_databento_source.py (new)
  
  Uses ohlcv-1d schema for daily bars. The cache key includes dataset, symbol,
  schema, start_date, and end_date. Cache files are Parquet format for fast
  loading. Metadata includes download_date for age validation.

dependencies_detail:
  - None - this is the foundation for Databento integration