fix: regenerate the bundled fixture against the sparsified corpus (#18)

The fixture predated three shipped corpus changes at once: no J rows in
summary_categories (it was built before the crosswalk completion), no
representation.parquet or code_set.parquet, and a still-dense wide era.
Every test in this package and in cog-api runs against it, so both suites
were green against a corpus that no longer exists. This is #18's stated
prerequisite; it proves nothing about production until it lands.

Regenerated from the publish tree at pipeline_commit 83f9715 (schema v6,
built 2026-07-29). FY2011 goes from 2,864,212 rows to 496,004 -- 82.7% of
the old partition was explicit zeros -- and the fixture now ships all ten
publish-tree metadata tables rather than six. The generator's file list is
a single constant now, so the copy step and the manifest step cannot drift.

Three test repairs, each a real consequence of sparsification rather than
a number to bump:

  test-categories.R          "assistance" joined the spending subtype
                             vocabulary with the J-prefix codes.

  test-spending.R            The harmonization block counts rows that
                             exist. Broward's E21/F21/G21 were zero-pads
                             and are gone, so the anchor moves to FL state,
                             whose three NA-mapped rows carry $2.83B --
                             the amount accounting was previously asserted
                             only against 0 and could not have caught a
                             bug. Broward keeps a test of its own, now
                             asserting the zero-pads are absent.

  test-expenditure-concept.R Coverage-gap suggestions are presence-based.
                             AL state's only FY2011 B47 cell was an
                             explicit zero, so ig_federal_b47_wide stopped
                             being a candidate there; FL state carries a
                             real amount, so the counterpart guard is
                             exercised against a suggestion that fires.

test-fixture-vintage.R pins the structural facts that separate this vintage
from its predecessor -- the ten metadata tables, the dense/sparse
representation contract, zero explicit zeros in FY2011, code_set coverage,
and J19's category. Checked against the old fixture: FY2011 carried
2,368,208 explicit zeros, so the assertion discriminates rather than
merely passing.

Suites: uscogdata 594 pass / 0 fail / 6 skip (was 576/0/6).
cog-api 357 pass / 0 fail / 8 skip against the regenerated fixture,
unchanged from its baseline.

NEWS.md

@@ -1,5 +1,31 @@
 # uscogdata 0.1.0 (development)
 
+## Bundled fixture regenerated against the sparsified corpus
+
+* `inst/extdata/fixture_corpus/` now tracks the corpus published on
+  2026-07-29 (`pipeline_commit 83f9715`, schema v6). The wide era no longer
+  stores explicit zeros: FY2011 fell from 2,864,212 rows to 496,004, of
+  which none are `$0`. **Absence now means two different things** — in a
+  `dense_source` year (≤ FY2011) an absent cell means Census published `$0`;
+  in a `sparse_source` year (≥ FY2012) it means not reported. The corpus
+  carries that rule in two new tables the fixture now ships,
+  `representation.parquet` and `code_set.parquet`, alongside
+  `census_collection_coverage.parquet` and `lineage_events.parquet`
+  (all ten publish-tree metadata tables, up from six). Catalogued upstream
+  as series break `SB194`.
+* `cog_categories()` gains an `assistance` spending subtype: the J-prefix
+  aid/benefit codes (`J19`, `J67`, `J68`, `J85`) are categorised now that
+  the upstream crosswalk covers every flow code carrying dollars.
+* Two consequences worth knowing about, both visible in provenance rather
+  than in returned dollars. The harmonization block's `na_rows_excluded`
+  counts only rows that exist, so wide-era codes that were zero-padded no
+  longer appear there. Coverage-gap `suggestions` are presence-based for the
+  same reason, so a recipe whose component codes were all `$0` for a given
+  government-year is no longer suggested for it.
+* `tests/testthat/test-fixture-vintage.R` pins these structural facts, so a
+  fixture left behind by a future publish fails loudly instead of letting the
+  suite pass against a corpus that no longer exists.
+
 ## Breaking: corpus schema_version 4 (Phase P canonical ids)
 
 * The package now requires corpus `schema_version = 4` (`MinCorpusSchema` /