lib/constants.py

"""
lib/constants.py

Single source of truth for competition-wide constants.

REFERENCE_DATE is pinned to the competition date rather than using
datetime.date.today() in each module. Using today() has two failure modes:
  1. Precompute runs at 23:58, rank runs after midnight → behavioral decay
     scores computed against different dates, making the parquet stale.
  2. A judge reproduces the submission months later → all recency scores
     collapse to 0 (every candidate "hasn't been active in N months") and
     the submission produces a different top-100 than was submitted,
     making Stage 3 reproduction fail the diff check.
Pinning to the competition date avoids both.
"""
import datetime

REFERENCE_DATE = datetime.date(2026, 6, 17)