fieldtest follow-up: G1 (DESIGN.md NaN-print Unspecified) + F1 roadmap entry

docs/DESIGN.md

@@ -2058,6 +2058,13 @@ no `f32` variant. The runtime / codegen contract:
   pattern is conformant; `0.0 / 0.0` may produce
   `0x7ff8000000000000` on one target and a different qNaN on
   another.
+- The textual rendering of NaN by `io/print_float`. The libc
+  `printf("%g", nan)` glue used by the runtime is permitted to
+  emit `nan` / `-nan` / `NaN` etc. depending on libc version and
+  the NaN's sign bit; AILang does not normalise this, since the
+  prose / surface-print paths render NaN as the explicit `"NaN"`
+  spelling and `io/print_float` is for human-readable output, not
+  round-trip.
 
 These are the Rust / Swift / standard-LLVM defaults — not
 research-grade reproducibility guarantees. The stronger guarantee