0003. Look-ahead is prevented by structure

Status: accepted (2026-09-25)

Context

Documentation-only rules against look-ahead fail with agents, which also carry memorized market history.

Decision

The context builder exposes arrays truncated at the information cutoff; prices are point-in-time adjusted from raw bars plus corporate actions; holdout rows are clipped before the engine starts; check enforces an import policy and runs a mutation test that perturbs every post-cutoff bar.

Consequences

A strategy cannot see the future through the framework. The mutation test is the regression guard.

Amendment (2026-09-26)

The mutation check compares decisions through the cutoff session inclusive (the decision for session cut may only use bars before cut), at three cutoffs and with bars scaled both down and up. The earlier version compared only decisions before the cutoff and so could not see a one-bar leak; a meta-test now injects that off-by-one into the context builder and requires the check to fail.