Forty explicit Marshal streams built from tag bytes rather than Marshal.dump,
so the corpus stays valid when Ruby changes what it emits. Thirteen must be
accepted, twenty-seven must be rejected across eight distinct error types.
The accept half is what gives the reject half meaning. A detector that
rejected everything would fail thirteen cases here, including legitimate
cycles, shared object references, symlink reuse, and fixnums at every encoding
width.
Provenance note, stated because it weakens the evidence: Codex was asked to
build this corpus and the request was blocked by its provider's content filter,
which reads constructing hostile streams as offensive tooling. The request was
not reworded to get around that. The corpus was therefore written by the same
model that wrote the detector, which is exactly the arrangement the split
exists to avoid, and it should be treated as weaker than the negative-count
findings Codex produced independently.
The boundary of what Codex can contribute here is now mapped. Defensive
research, packaging research, defensive design and acceptance criteria, and
probing the parser during a design task all succeeded. Researching gadget
chains and building a hostile corpus were both refused.
Also fixes a bug in the corpus fixnum encoder, which computed the width marker
as width plus 256 and raised RangeError for any positive multibyte value.
110 tests, 244 assertions across five suites.
8ce093260c