balance is the only category_type whose subtype column is not orthogonal to
category. Measured against the crosswalk: 5 of 6 expenditure subtypes and 1 of
7 revenue subtypes span more than one category, but 0 of 5 balance subtypes do.
Balance is a strict tree -- Fund Balances = {general}, Retirement System
Holdings = {employee_retirement}, Insurance Trust Balances = the three trust
subtypes.
Exposing both arguments would admit no useful combination: of the 15 pairs, 3
are redundant and 12 are guaranteed empty for every government in every year,
failing as an empty tibble that reads as "holds none" rather than as a
contradiction.
Dropping it also keeps the verb aligned -- no uscogdata verb exposes a subtype
argument; the API layers its own subtype row filter on top, which cog-api#26
can do for /balances. #25's one-filter requirement is still met, since
category = "Fund Balances" is exactly W01/W31/W61.
Adds two tests: that one-filter equivalence, and an assertion that the
subtype -> category tree holds, so an upstream change making category lossy
fails here rather than in a user's analysis.
Requirement 1 of #25 shipped with #11/#12. This specs requirement 2 only.
Records three upstream gaps found while measuring the corpus, which change
the shipping scope:
- X40/X41 carry ~42.7K rows (1967-2011) but have no summary_categories row,
so they cannot appear in a category_type='balance' view. Both holdings
recipes span X40/X41 + Z77/Z78, so recipe= would silently return only the
2012-2016 leg. recipe= is therefore deferred to v2.
- SB195/SB196 attach to fin_code X40/X41, outside the balance view.
- SB197-SB202 attach to flow codes, not the holdings codes, so the FY2016
termination of X21/X30/X42/X44/X47/Z77/Z78 has no catalogued break.
Caveats 2-4 are therefore surfaced reader-side via a computed coverage_window
rather than through the existing series-break builders.
jared