id: DATA-DB-004
title: Backtest Page UI Updates
status: backlog
priority: high
dependencies:
  - DATA-DB-001
  - DATA-DB-002
estimated_effort: 2 days
created: 2026-03-28
updated: 2026-03-28

description: |
  Update backtest and event comparison pages to support Databento data source
  and independent scenario configuration. Show estimated data cost and cache
  status in the UI.

acceptance_criteria:
  - Data source selector shows Databento and yFinance options
  - Databento config shows dataset and resolution dropdowns
  - Dataset selection updates cost estimate display
  - Cache status shows age of cached data
  - Independent start price input (0 = auto-derive)
  - Independent underlying units and loan amount
  - Event comparison page uses same data source config
  - Settings persist across sessions

implementation_notes: |
  Page changes:
  
  Backtests page:
  - Add "Data Source" section with Databento/yFinance toggle
  - Add dataset selector (XNAS.BASIC for GLD, GLBX.MDP3 for GC=F)
  - Add resolution selector (ohlcv-1d, ohlcv-1h)
  - Show estimated cost with refresh button
  - Show cache status (age, size)
  - "Configure Scenario" section with independent start price/units
  
  Event comparison page:
  - Same data source configuration
  - Preset scenarios show if data cached
  - Cost estimate for missing data
  
  State management:
  - Use workspace-level BacktestSettings
  - Load on page mount, save on change
  - Invalidate cache when params change

dependencies_detail:
  - DATA-DB-001: Need DatabentoHistoricalPriceSource
  - DATA-DB-002: Need BacktestSettings model