feat: accept corpus schema v6 (FIPS geography harmonization); v6 fixture

Schema v6 (cog_pipeline 2026-07-22) renamed the long table's
fips_state_code/fips_county_code to fips_state_asof/fips_county_asof and added
cog_legacy_state/cog_legacy_county (26 -> 28 cols). This package references
none of those columns and its geography always came from
canonical_fips_xwalk (already present-based), so acceptance is a version-set
bump: supported = c(4L, 5L) -> c(4L, 5L, 6L) in .validate_schema() and
cog_open(). A prominent note in .validate_schema() documents the SILENT
semantic change for raw-long readers: long fips_state/fips_county are now
PRESENT/harmonized geography (carried back per government), not as-of-year.

Fixture regenerated from the published v6 tree (schema_version 6, 28 cols).
Test updates:
  * test-manifest.R: v6 accepted; boundary rejection moves to v7.
  * test-spending.R: the na_rows_excluded pin (0) predated the Task 18 map
    extension, which added E/F/G-prefix discontinued_na rulings (E21/F21/G21,
    Education NEC local, SB184-186). Broward's 2011 partition zero-pads
    exactly those codes: 3 NA-harmonized rows excluded, all amt=0, so the
    excluded AMOUNT pin stays 0. Data-verified against the v6 fixture.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

R/manifest.R

@@ -128,7 +128,17 @@
 }
 
 #' @noRd
-.validate_schema <- function(manifest, supported = c(4L, 5L)) {
+#' Schema v6 (FIPS geography harmonization, 2026-07-22) is accepted alongside
+#' 4/5. v6 renamed the long table's fips_state_code/fips_county_code to
+#' fips_state_asof/fips_county_asof and added cog_legacy_state/
+#' cog_legacy_county (26 -> 28 cols); this package references NONE of those
+#' columns, so no code change was needed. NOTE the SILENT semantic change for
+#' any consumer of the raw long table: long fips_state/fips_county are now
+#' PRESENT/harmonized geography (current county identity carried back to every
+#' year, matching canonical_fips_xwalk) rather than as-of-year; as-of-year
+#' moved to the *_asof columns. This package's own geography always came from
+#' the xwalk (already present-based), so behaviour is unchanged.
+.validate_schema <- function(manifest, supported = c(4L, 5L, 6L)) {
   if (!manifest$schema_version %in% supported) {
     cli::cli_abort(c(
       "Corpus schema version mismatch.",

R/session.R

@@ -12,7 +12,7 @@ cog_open <- function(url = .resolve_url(),
   DBI::dbExecute(con, "INSTALL httpfs; LOAD httpfs;")
 
   manifest <- .fetch_or_cache_manifest(url, cache_dir)
-  .validate_schema(manifest, supported = c(4L, 5L))
+  .validate_schema(manifest, supported = c(4L, 5L, 6L))
   .validate_scope(manifest)
 
   .register_views(con, url, manifest)