New top-level section '## Roundtrip Invariant' between Decision 11
and '## Mangling scheme'. States both directions of the .ail.json
↔ .ailx bijection, names Float-bits-hex encoding as the in-
invariant mechanism (not an exception), lists the four enforcement
tests by path, and explains why the property is top-level
(load-bearing on language identity, not on Decision 6's surface-
design rationale).
Decision 6 Constraint 2 rewritten as upward cross-reference to the
new section; the substantive content now lives at the anchor.
Direct boss edit (no planner/implement dispatch): spec Architecture
#1 fully specified the content, no design judgement deferred to
execution. The iter is a deterministic projection of the spec
onto DESIGN.md prose.
Brummel
e3b0dd20c5