The week-parity regression test (D-004): walks a two-week alternating
rotation day by day across a FULL 366-day leap year (2020) and a full
365-day year with 53 ISO weeks (2015), asserting the present-day
sequence never breaks or inverts, including January 1st. The
expectation is derived from the anchor's 7-day blocks — each block
uniform, consecutive blocks alternating — not from the engine's own
index formula, so a parity-based implementation that resets on
January 1st breaks block uniformity or alternation (most visibly in
the block spanning the boundary). Year facts asserted: 2020 = 366
days and ISO week 53; 2015 = 365 days and ISO week 53. The test
docstring names itself as the regression guard. Suite: 1004 passed.
Joshua King
20d7efb04b