diff --git a/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md b/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md
index a2e8d4b8..6b562d78 100644
--- a/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md
+++ b/03-DESIGN/01-to-be/47-milestones/G-20-lead-answers.md
@@ -21,3 +21,10 @@ names the principle that settles it, and is cited as "design 47 G A-n".
 - **A-2** (§655; principle 7, the rule that code shared between modules lives in mesh-sdk) `nats-tools/internal/busarchive`
   moves whole with `bussnap` into mesh-sdk as its own package `go/busarchive`, its tests with it; every other importer
   (verify, the nightly dump) imports it from there, and no copy stays in mesh-catalog.
+- **A-3** (§686, §640, §687; principle 7; replaces A-1) The generated contract types stay as they are, plain structs whose
+  fields every importer already reads; nothing is generated for the writer and no field is renamed. mesh-sdk's writer is
+  generic over the contract's body types (`Writer[F, C, S, A any]`, one type parameter per body) and works on their wire
+  form: it marshals a body, reads and sets `kind`, `scope`, `id`, `subject`, `at` and `since` by their contract names,
+  and runs `views.CheckFinding` on that form. A body whose wire form lacks a field the contract names fails loudly at its
+  first write (principle 3) and in the writer's unit test, which runs against the real generated types of
+  `mesh-conditions`.