Replaying live books over past sessions used today's constituent list for
every day, so US books bought names (BE, MRVL, ILMN, FLEX, P) before they
joined the S&P 500. session_universes/session_signals now compute each past
session on that day's members (S&P change log, CSI 300 snapshots); the
latest session keeps the live list. Used by auto/monitor catch-up, replay
and simulate. _run_session takes precomputed targets only.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>