- Add WalkForwardResult model with train/test window metrics
- Create WalkForwardEngine that reuses existing BacktestEngine
with rolling train/test window splits
- Add POST/GET /api/backtest/{id}/walkforward endpoints
- Add Walk-forward tab to backtest detail page with parameter
controls, cumulative return chart, and window results table
- Add Alembic migration for walkforward_results table
- Add 8 unit tests for window generation logic (100 total passed)
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Pydantic v2's model_dump(mode="json") serializes Decimal as strings (e.g.,
"33.33" instead of 33.33), causing frontend crashes when calling .toFixed()
on string values. Introduced FloatDecimal type alias with PlainSerializer
to ensure Decimal fields are serialized as floats in JSON responses.
Also fixed frontend Transaction interface to match backend field names
(created_at → executed_at, transaction_type → tx_type).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
