Add a point-in-time (PIT) factor/data store and a score provider so the
backtest engine can rebuild per-symbol scores from data actually knowable
at a given date, instead of silently reusing the live board:
- backend/app/factor_vintages.py: append-only, provenance-complete store
(observed_at/released_at/retrieved_at) with a SHA-256 canonical hash chain.
value_at(as_of) only ever returns rows whose released_at <= as_of (real,
testable anti-look-ahead); no value by as_of fails closed (returns None).
- backend/app/pit_scorer.py: PitScoreProvider computes theme surprises from
PIT factor values only, and a partial siamchart fundamental view (EPS
growth from the 5-year series; current ratios marked partial). score_board
attaches pit_meta so callers can tell PIT from fallback.
- backend/app/backtest.py: _resolve_scores now sets leakage_guard ONLY when
the supplied score_fn's meta asserts pit_meta.pit=true; an arbitrary
callable with no PIT proof is no longer treated as PIT (closes the
'supplied fn => PIT' hole).
- backend/app/__init__.py: /api/v1/backtest accepts use_pit, wiring the PIT
provider; _load_siamchart_snapshot loads the SET50 fundamental snapshot.
- tests: factor store (9), pit scorer (5), backtest leakage-guard gating (2
new + 1 corrected) — full backend suite 255 passed. Empty store fail-closes
(leakage_guard=false) as proven by a live route probe.
Honest scope: theme dimension is PIT from this store forward; siamchart
fundamental remains partial (current ratios) and is flagged as such. No
historical factor data before today exists, so pre-today backtests remain
non-PIT by construction.
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