Reconciles the two Hands' independently-regenerated parity vectors
(Soul's whole-cut pass, F3): the C# fixture used schema *names*
("leaf_a") as literal ids, the Rust fixture used invented fake
sha256-shaped ids - every vector carrying an id failed when read by
the other runtime.
Adds contracts/cultnet/interop/selection-vectors.fixture.json: the one
row set both writers now build from, keyed by each schema's real
SHA-256 content-hash id exactly as CultDocumentRegistry computes it
(dumped via a temporary DumpFixtureSchemaIds run). Carries the rows
either runtime needs - astral/BMP-private-use keys, a float tie,
cites/cited, a cites target reached by alias - plus two DIFFERENT
alias forms, because the two runtimes' alias matchers key off
different descriptor attributes and no single candidate resolves
through both (see the fixture's "//aliases" note and the report).
Rewrites SelectionParityVectorTests.cs to load the fixture instead of
hand-building rows (BuildFixture/BuildExtendedFixture deleted), assert
the fixture's declared schema ids still match what the registry
computes (fails loudly on drift instead of silently comparing wrong
ids), and use the real schema id (not SchemaName) as a row's
cross-runtime identity. Also fixes a real bug this file carried since
before the shared fixture: both the writer and the reader compared
`evaluation.Rows.Count` (the page size) against "matched" instead of
`evaluation.TotalMatched` (the total, per R-G) - selections with a
Limit were writing/checking the wrong number. The reader now collects
every vector's mismatch instead of stopping at the first one, so a
real parity defect is reported in full.
Regenerates selection-vectors.cs-written.json from the shared fixture.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>