id: BT-005
title: Defer Entry Spot Derivation to Backtest Run
status: backlog
priority: P1
effort: S
depends_on: []
tags: [backtesting, ux, performance]
summary: Only derive entry spot from historical data when user clicks Run, not on every form change.
acceptance_criteria:
  - Entry spot is NOT fetched when user changes start/end dates.
  - Entry spot is NOT fetched when user changes other form fields.
  - Entry spot IS derived when user clicks the Run button.
  - Form remains responsive during date/field changes (no API calls blocking).
  - Clear loading indicator shows when entry spot is being fetched during run.
  - Previous entry spot value is retained until new one is derived.
notes:
  Current behavior calls derive_entry_spot on every date change which causes
  API errors if user is still configuring other fields.
  
  The refresh_workspace_seeded_units function should not be called on date changes.
  Entry spot derivation should happen inside start_backtest or as a separate
  explicit "fetch spot" button if user wants to preview.