The cross-implementation corpus (req:binfmt:decode-vectors) covered ops and
bundle but nothing from epiphany-core — the oldest and most load-bearing wire
in the repo had no vectors at all. 65 -> 93 vectors, 5 -> 19 surfaces.
This delivers a revision the companion had already ordered. binary_format.tex
asked for the corpus to extend to the representative layouts "which remain
round-trip locked rather than literal-byte locked" — a description, written in
advance, of the exact defect found in tranche 3b-i: swapping smufl and
overrides in BOTH halves of ScoreTuningContext's codec silently moved a
permanently frozen layout and passed all 1283 tests and 8/8 conformance. An
encoder and decoder that agree on the wrong order round-trip perfectly. Only
literal bytes can see it.
That mutation is now the mandatory regression vector
(core.score_tuning_context/overrides_before_smufl), and re-applying the swap
was verified to fail three ways: the corpus reports "declared reject, but was
ACCEPTED", the committed corpus goes stale, and the conformance suite fails.
Both the full workspace suite and conformance now catch what previously passed.
Almost no new machinery was needed: CanonicalValue was already public and
already did decode + finish() + re-encode + reject-on-mismatch, and already
covered four of the five representative layouts. RationalTime joins it (the
fifth, and the exemplar of the spec's own warning that an outer guard can mask
a lenient inner codec — it reduces to lowest terms on decode, so only
hand-written bytes reach that path), along with the five schema-major-3 types.
check() therefore calls real production API, not a harness-side wrapper: a
leaf reject vector exercises the code an external implementer must match.
Codec and Reader stay pub(crate); the only new public item is `pub mod
vectors`.
Two things deliberately shaped: core is appended LAST in the testkit chain, so
the regenerated corpus diff is purely additive — 56 insertions, 0 deletions,
which PROVES no existing vector's bytes moved and therefore that no existing
wire form changed. And the per-major Score vectors assert canonical_bytes()
equality only at major 3: majors 0-2 migrate by design, rewriting the bytes,
and their canonicality at their own major is already established by the frozen
per-major encoder's re-encode guard. Comparing there would fail on every
vector and invite "fixing" it by gutting the vector's meaning.
Also rebuilds binary_format.pdf, which commit 68b08ad should have carried and
did not — every other binary_format.tex commit includes it. The rebuild picks
up both that tranche's Schema Major 3 section and this one. latexmk -xelatex
twice: 0 errors, 0 undefined references, 60 pages.
Gate: fmt clean, clippy 0, 1321 passed / 0 failed, doc 0, conformance 8/8 with
gate [7d] reporting 93 vectors, requirement labels 6/6 at 212/282/282 (no new
req: labels).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Levi Neuwirth
d96d79b8ba