Unadjusted prices, with corporate actions as a separate series
Equity price history can be stored back-adjusted (splits and dividends folded into historical prices) or as-printed. We store as-printed prices and carry splits and dividends as a separate dated event series. The engine treats a price move explained by a corporate action as a known event rather than a gap: the stop does not fire, and the position is adjusted.
Considered options
- Back-adjusted closes. The standard choice, one series, no extra dependency. Rejected for two reasons. It is restated history, which is the precise failure the point-in-time rule exists to prevent — the equity form of reading tomorrow's newspaper. And the adjustment factor changes retroactively every time a dividend is paid, so an archived run stops reproducing with no code change at all. Reproducibility would fail silently, which is worse than failing.
- Unadjusted with no actions series. Cheapest and point-in-time correct, but a 4:1 split reads as a -75% gap through every stop and every dividend as a fake overnight loss. Results on any multi-year series would be wrong in a direction that looks exactly like real drawdown.
Consequences
A corporate-actions source becomes a required dependency, possibly a paid one — it needs a question and a price in M0, against a data budget already at $128.09 of $150 with free credit exhausted.
A related defect was found while deciding this, and is not itself an architectural decision: the donor data adapters cannot serve this project. oldschool-investor/src/osi/stooq.py is unusable live (its own header records a JavaScript browser-check returning HTML since 2026-07), and both it and the working yahoo.py parse close only — no high, no low. Without highs and lows there is no way to know whether price touched a stop, and stops are mandatory (ADR-0003). The equity data path is a new component, not a donor reuse. The task list must be corrected accordingly.