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

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