Task 7 (final) of the expenditure_concept plan. The vignette leads with the
two archetype questions -- a single government's own trend (either concept
works, held fixed across years) vs a cross-government rollup (direct only,
with the refusal error from cog_geographic_rollup() shown and explained) --
walked through with code that runs against the bundled fixture corpus
(years 2011/2012/2019/2020, substituting for "2017 vs today"). Explains the
double-counting mechanism (a state's M44 payment to a county is the same
dollar as the county's own E44/F44), why Total = Direct + M + L rather than
Direct + M, and the composition rules (expenditure_concept is orthogonal to
basis, mutually exclusive with recipe). README gets a short pointer section
with the one-line rule.
jared