v4 open holdout, ±10/±30/±60, raw and percent priors: only 4/9/14 of 57 day-precision training events split candidates; widths unchanged, top-1 drops. Narrowed year blocking (R3) mixed. All arms no_benefit; no implementation brief recommended. Two runs byte-identical. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017eEAG8HD3mm8gsKXgk8uU8