feat(fixed): add Q32.32 deterministic fixed-point arithmetic

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

pkg/fixed/nofloat_test.go

@@ -0,0 +1,52 @@
+package fixed_test
+
+import (
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+)
+
+// Determinism depends on there being no floating-point arithmetic anywhere in
+// the simulation path: floats drift between architectures and between native
+// and WASM builds, which would silently break round verification. This test
+// fails the build if a float type is ever introduced.
+//
+// Test files are exempt, since statistical assertions legitimately use floats.
+func TestNoFloatingPointInDeterministicPackages(t *testing.T) {
+	for _, dir := range []string{".", "../sim"} {
+		if _, err := os.Stat(dir); os.IsNotExist(err) {
+			continue
+		}
+		fset := token.NewFileSet()
+		pkgs, err := parser.ParseDir(fset, dir, nil, 0)
+		if err != nil {
+			t.Fatalf("parse %s: %v", dir, err)
+		}
+		for _, pkg := range pkgs {
+			for name, file := range pkg.Files {
+				if strings.HasSuffix(name, "_test.go") {
+					continue
+				}
+				ast.Inspect(file, func(n ast.Node) bool {
+					switch node := n.(type) {
+					case *ast.Ident:
+						if node.Name == "float32" || node.Name == "float64" {
+							t.Errorf("%s: forbidden float type %q in deterministic package",
+								filepath.Base(name), node.Name)
+						}
+					case *ast.BasicLit:
+						if node.Kind == token.FLOAT {
+							t.Errorf("%s: forbidden float literal %s",
+								filepath.Base(name), node.Value)
+						}
+					}
+					return true
+				})
+			}
+		}
+	}
+}