diff --git a/docs/DESIGN.md b/docs/DESIGN.md
index 46e89e7..16bc820 100644
--- a/docs/DESIGN.md
+++ b/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
diff --git a/docs/roadmap.md b/docs/roadmap.md
index 44d4e3d..0d32a5b 100644
--- a/docs/roadmap.md
+++ b/docs/roadmap.md
@@ -91,6 +91,15 @@ work progresses.
 - [ ] **\[todo\]** 21'h iteration — final 21' carry-over (latency
   methodology pass). Numbering kept for continuity with the 21' arc.
 
+- [ ] **\[todo\]** `io/print_float` always-emit-`.0` — surface
+  printer always emits `.` or `e/E` so re-lex routes to Float;
+  the runtime printer (`printf("%g\n", v)`) doesn't, so `2.0`
+  prints as `2` (Int-shaped). Asymmetric. Either switch the
+  runtime path to a `.0`-fallback printer (matching surface) or
+  document the `%g` contract in DESIGN.md §"Float semantics" so
+  the LLM-author knows `io/print_float`'s output is for-humans
+  not round-trip.
+  - context: `docs/specs/2026-05-10-fieldtest-floats.md` finding F1.
 - [ ] **\[todo\]** Rustdoc warning sweep — `cargo doc --no-deps`
   reports 16 pre-existing warnings (15 in `ailang-check`, 1 in
   `ailang-core`: private-item links from public doc, unresolved