Milestone-close audit found three drift items (architect) plus
two carry-on items; bench all-green.
Fixes (rt.tidy, boss-direct):
- 5th test parse_then_print_then_parse_is_idempotent_on_every_ailx_fixture
enforces Direction 2 of the Roundtrip Invariant directly. The
DESIGN.md enforcement list grows from four to five tests.
- docs/roadmap.md P1 'Round-trip completeness invariant' entry
retired with one-line journal mirror per roadmap convention.
- DESIGN.md wording sync: <16-hex> → <16-lowercase-hex> for the
Float-bits-hex spelling in the new section (matches §Data model).
Milestone closed clean; five workspace-wide tests anchor the
.ail.json ↔ .ailx bijection plus AST-variant coverage.
