Add round() → f64.nearest support in WAT code generator

The WAT generator was silently emitting `f64.const 0` for calls to
round()/arrondir(), causing incorrect results (always 0) in WASM
modules that use rounding. Add _ROUND_NAMES to the builtin alias set
and lower round(x) to the f64.nearest instruction.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: johnsamuelwrites

multilingualprogramming/codegen/wat_generator.py

@@ -83,6 +83,7 @@
     _FILTER_NAMES,
     _INPUT_NAMES,
     _INT_NAMES,
+    _ROUND_NAMES,
     _LEN_NAMES,
     _MAP_NAMES,
     _MAX_NAMES,
@@ -1133,6 +1134,10 @@ def _gen_expr(self, node, indent: str):  # noqa: C901  # pylint: disable=too-man
             elif resolved_fname in {"math.sqrt", "sqrt"} and len(node.args) == 1:
                 self._gen_expr(node.args[0], indent)
                 self._emit(f"{indent}f64.sqrt")
+            elif fname in _ROUND_NAMES and len(node.args) == 1:
+                # round(x) → f64.nearest (IEEE 754 round-half-to-even)
+                self._gen_expr(node.args[0], indent)
+                self._emit(f"{indent}f64.nearest")
             elif resolved_fname in {"math.floor", "floor"} and len(node.args) == 1:
                 self._gen_expr(node.args[0], indent)
                 self._emit(f"{indent}f64.floor")

multilingualprogramming/codegen/wat_generator_support.py

@@ -40,6 +40,7 @@ def _aliases_for(canonical: str) -> frozenset:
 _MAX_NAMES = _aliases_for("max")
 _LEN_NAMES = _aliases_for("len")
 _INT_NAMES = _aliases_for("int")
+_ROUND_NAMES = _aliases_for("round")
 _POW_NAMES = _aliases_for("pow")
 _SUM_NAMES = _aliases_for("sum")
 _LIST_NAMES = _aliases_for("list")