Thirteen drift-locked document vectors -- four accept, nine reject, one per
implemented rejection class -- gated as conformance step [7e] beside [7d]'s 65
decode vectors.
The checker distinguishes three outcomes, and that distinction is the whole
point. `Rejected`, `AcceptedCanonical`, and `AcceptedNonCanonical` are separate
verdicts, and every one of the four wrong pairings is a failure: an accept vector
that merely normalizes fails, and a reject vector that is accepted -- whether as
canonical or after normalization -- fails. The decode corpus learned this the
expensive way, where collapsing "rejected" with "accepted but normalized" let a
corpus pass against the exact decoders it was written to catch.
Accept vectors assert the byte-checkable equation `project(serialize(parse(T)))
== T`, which quantifies over TEXTS. The comments say plainly that it must not be
replaced with bundle identity, and name the three deliberate binary losses --
duplicate blobs collapsing under derived-ordering, regenerated physical layout,
and dropped accelerators -- so the next reader does not "fix" it into a bundle
comparison and then chase a phantom.
Reach is asserted exactly, not merely non-zero: two documents each carrying an
extension, a canonical base, a custom profile, a lineage, and more than one
envelope; and every reject class must have exactly one vector the parser really
refused. A mislabelled reject drops its class to zero rather than collecting
credit from its label.
The corpus was verified by breaking the implementation, not the checker: making
`parse_document` silently tolerate a missing trailing LF is caught three ways,
and the suite reports "declared reject, but was ACCEPTED and normalized".
Review fixed one defect in the semantic harness. It claimed to check
`semantics(parse(project(B))) == semantics(B)` but compared `parse(project(B))`
against `document_from_bundle(B)` -- and `project_bundle` *is*
`project_text_document(document_from_bundle(..))`, so both sides flowed through
one function and any bug in it cancelled out. Dropping an envelope there passed.
It now compares against the envelopes the test itself serialized in, which is
independent of the projection path; the same mutation fails.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
spec/vectors/decode_vectors.txt -- 37 committed byte strings across five
surfaces, each with its normative accept/reject verdict. The reference
implementation's fuzzers prove its own decoders self-consistent, which says
nothing about whether a foreign decoder agrees with the format. This is what one
is checked against. Gated in the conformance suite as [7d], and drift-locked:
the committed file must equal vectors::render(), so a wire-format change lands
in the diff.
It found a real defect on its first run. OperationKindTag::TransposeInterval
encoded to [30] and its own decoder REJECTED it -- Push 4a added the variant to
discriminant() and never to decode_canonical. OperationKindTag is what edit
barriers persist, so a barrier prohibiting TransposeInterval could be written and
never read back. Silent data loss on reopen.
Four things should have caught it. None did, and two made it worse:
The round-trip test enumerated DISCRIMINANTS -- (0u8..30).map(decode_canonical)
-- starting from bytes the decoder already knew, so it structurally could not
notice a variant the decoder was missing. It now enumerates VARIANTS from one
all_tags() list, with a completeness check in both directions.
The distinctness test's hand-written variant list omitted it too. Same list now.
operation_kind_tag_decode_rejects_malformed_bytes asserted that tag 30 is
REJECTED, and layout-ir's decode_rejects_unknown_discriminants asserted the
same at the barrier surface. Both were locking the bug in place and made it
look deliberate. Both now name 31, and a new barrier test round-trips a barrier
prohibiting every tag -- the persistence surface where this actually bites.
The P2 decode fuzzer fed valid corpus bytes to the tag decoder and tallied the
failure as a REJECTION, like any garbage input. It never asserted that an
unmutated corpus entry decodes. Both fuzzers now do, as a pre-pass.
The harness had the same disease as the code. `check` collapsed "rejected" with
"accepted but does not re-encode", so a decoder that silently normalizes
non-canonical bytes PASSED the reject vectors it was written to catch. Verified:
removing the whole-state guard, and restoring the lenient compression codec, both
left the corpus green. `check` now returns Ok(injective) for accept and Err for
reject and never conflates them -- silently normalizing non-canonical bytes IS
accepting them. With that fixed, all four defect mutations fail the corpus, each
naming its class.
The corpus pins one vector per class this repo has shipped a bug in:
non-canonical-map-order (a guard catches it; no per-site check exists),
non-canonical-vec-order (only a per-site check catches it; a guard is blind),
lenient-sub-codec (a guard masked it in the manifest; the index had none), plus
trailing-bytes, truncated, unknown-discriminant, count-exceeds-remaining. A test
fails if one goes missing.
Gate: fmt clean, clippy 0, 30 targets / 1024 passed / 0 failed, docs 0 under
-D warnings, conformance 8/8 (now including [7d]), zero golden churn.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Levi Neuwirth