Two suites pin that the windowed slope / r2 / population-sd composed from
the rollup accumulators equals the live Postgres REGR_SLOPE / REGR_R2 /
STDDEV_POP over the same raw rows.
compose-regression.test.ts (container-free) builds per-DAY-bucket
accumulators from a raw fixture exactly as the populator's SUM terms do,
then asserts composeRegression over those buckets equals a direct OLS over
the flat raw rows - the same closed form Postgres folds - on an uneven
multi-bucket fixture, plus the coverage contract (NULL accumulator,
< 2 readings, and zero-x-variance all return a full miss so the reader
falls back to live SQL).
rollup-regression-parity.integration.test.ts (real Postgres testcontainer)
seeds raw measurements across many uneven DAY buckets, folds the rollups,
and compares the accumulator compose to live REGR_*/STDDEV_POP to <= 1e-9:
a single-source WEIGHT series, a dual-source RHR series proving the
source-collapse runs BEFORE accumulator summation (composed == live WHOOP
-only, != the cross-source blend), and a DST-boundary series confirming
the UTC epoch-day x-axis parity-matches across the transition.
The residual is pure floating-point reassociation (per-bucket-then-window
vs flat summation), orders of magnitude below the read tier's rounding.
Marc-André Bombeck
4706120879