* docs(design): derive the exact Particle Valid (Restriction) procedure
The false-negative tail (particles*/elemZ) routes through one approximate
oracle, ParticleRestriction.violation. Rather than patch cases, derive the
exact XSD 1.0 3.9.6 decision procedure once, clean-room from the spec and the
Xerces reference algorithm, with the soundness (no-false-positive) argument for
each clause: normalization, substitution-group expansion, effective total
range, the compositor dispatch table, and the rcases.
Identifies the closeable gaps (subst-group expansion for elemZ026/V020,
MapAndSum effective-total-range, NameAndTypeOK union-member derivation) and
names the genuine spec limitations (Ha161/Z001 contradiction, mgO013 contested,
union-member by-name derivation) as bounded, not bugs. Sets the implementation
order, each clause gated by the proof plus the XSTS valid-rejected=0 gate and an
adversarial over-rejection critic. No behaviour change.
* docs(design): record the empirical finding -- particle-restriction tail is contested
Probing the actual cases overturned the first hypothesis. elemZ026 and
particlesV020 are the same pattern (a derived ref to a substitution-group
MEMBER restricting a base ref to the HEAD), and PureXML already accepts them
because its content model expands a head ref to admit members (for instance
validation), which the restriction oracle inherits -- the Xerces-lenient
reading. They are CONTESTED (Xerces/PureXML accept, XSTS rejects under strict
NameAndTypeOK), so the keystone (adding expansion) would entrench the
acceptance, not close them; closing them risks a false positive. Every
remaining particle case is contested or FP-delicate, so the exact-oracle
keystone yields no clean conformance win. The remaining lever toward the full
bar is the proven resource bound (pushdown matcher), not this oracle. Proof
first earned its keep: it prevented shipping against contested targets.
The Unique Particle Attribution check no longer inlines group references or caps.
A new CompositionalDeterminism engine computes first/followlast over particle
identities and summarizes each xs:group once, so a multiply-referenced nested
group whose inlined Glushkov automaton would be 2^K positions is checked in
O(nodes * particles^2) time. ContentModelDeterminism now delegates to it and the
inlining position automaton plus positionCap are deleted, closing the last named
interactive-safety resource-bound blocker (production-readiness stopper #4) and
the silent under-rejection the cap caused (stopper #3).
The compositional engine was proven verdict-equivalent to the prior inlining
automaton by a differential over the entire XSTS corpus (zero divergences) before
replacing it. The followlast detail was essential: a first attempt that emitted a
repeating end-item's loop-back and the suffix-first as separate decision sets
under-detected 13 XSTS content models; the differential caught every one.
Verification: XSTS gate unchanged (invalid-schemas-accepted 15, valid-schemas-
rejected 0, instance buckets held); SchemaDeterminismGroupBlowupTests compiles a
2^20-position model without hanging and rejects an ambiguous one the old cap would
have skipped (WASI uses a smaller depth, native time limits gated off WASI); full
suite, style, namespacing, and WASM all pass. The per-particle model and QName-only
overlap are preserved, so the false-positive direction stays at zero.
Turns the 'blocked design frontier' for ContentModelDeterminism.positionCap into
a ready-to-implement, FP-safe plan derived from the current engine. Documents the
root cause (group-ref inlining gives 2^K positions), why naive position
dedup/sharing is unsound (cross-context followpos merge = false positive), the
sound compositional algorithm (per-group memoized nullable/firstParticles/
lastParticles/followlast over particle identities, cross-boundary conflicts
computed per reference-site by the parent, the star condition for repetition,
bounded O(nodes x particles^2)), and the differential-gated rollout (build
alongside the inlining oracle, prove verdict-equality on XSTS + a group-ref fuzz,
only then switch and delete the cap) with acceptance criteria.
