Brummel
e3b0dd20c5
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.