Add an append-only, hash-chained store of every collected Siamchart
fundamental snapshot so the 40% fundamental dimension can be reconstructed
at a historical date instead of always reading the latest snapshot:
- backend/app/siamchart_vintages.py: SiamchartVintageStore persists each
snapshot under its retrieved_at with a SHA-256 canonical hash chain
(tamper/reorder detectable); snapshot_at(as_of) returns the newest
snapshot whose retrieved_at <= as_of (anti-look-ahead), and fails closed
(returns {}) when none is knowable yet. Deduplicates identical
retrieved_at+body persists.
- backend/app/pit_scorer.py: PitScoreProvider accepts siamchart_store; when
wired, siamchart_factor_view reads the snapshot knowable at as_of
(pit_grade='pit') instead of the current snapshot (pit_grade='current').
score_board no longer forces partial_pit when a store is present — the
fundamental dimension is PIT; the theme dimension still fails closed
(pit=false) unless every theme factor has a released PIT value by as_of.
- backend/app/__init__.py: /api/v1/backtest use_pit seeds the first vintage
from the current snapshot (idempotent) and wires the store.
- tests: store (6) + scorer-with-store anti-look-ahead (1) — full backend
suite 273 passed.
Honest scope: snapshots are stored whole and reconstructible forward;
EPS year-keys inside a snapshot are not tied to calendar years, so EPS
growth stays latest-vs-prior (not fiscal-year-pinned). No history before the
first collected snapshot exists.
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