fix: Complete Scene VarDecls codegen and fix mage WASM build issues

This commit completes the declarative reactive transform implementation
by fixing the code generation and build system:

Codegen fixes:
- Generate VarDecls in Scene's RenderScene method body
- Add WithGeometry, WithMaterial, BindRotation to runtime functions list
- Properly structure method body with variable declarations before return

Magefile fixes:
- Exclude pkg/runtime from Test() - WASM tests require browser runtime
- Exclude pkg/runtime from Build() - needs WASM build tags
- Align with CI workflow which tests/builds WASM packages separately
- Add explicit package lists matching CI behavior

This enables scene_gen.go to properly include local variable declarations
like rotZ and use the new reactive binding functions with runtime. prefix.

Author: claude

magefile.go

@@ -39,16 +39,44 @@ func Vet() error {
 	return sh.RunWith(env, "go", "vet", "./pkg/runtime/...")
 }
 
-// Test runs all tests
+// Test runs all tests (excluding WASM-only packages)
 func Test() error {
 	fmt.Println("Running tests...")
-	return sh.RunV("go", "test", "./...")
+	// Test non-WASM packages (exclude runtime which requires WASM runtime to execute)
+	packages := []string{
+		"./cmd/...",
+		"./internal/...",
+		"./pkg/ast",
+		"./pkg/codegen",
+		"./pkg/parser",
+		"./pkg/visitors",
+	}
+	for _, pkg := range packages {
+		if err := sh.RunV("go", "test", pkg); err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
-// Build builds all packages for native target
+// Build builds all packages for native target (excluding WASM-only packages)
 func Build() error {
 	fmt.Println("Building native packages...")
-	return sh.RunV("go", "build", "./...")
+	// Build non-WASM packages (exclude runtime which is WASM-only)
+	packages := []string{
+		"./cmd/...",
+		"./internal/...",
+		"./pkg/ast",
+		"./pkg/codegen",
+		"./pkg/parser",
+		"./pkg/visitors",
+	}
+	for _, pkg := range packages {
+		if err := sh.RunV("go", "build", pkg); err != nil {
+			return err
+		}
+	}
+	return nil
 }
 
 // BuildWasm builds the runtime package for WebAssembly

pkg/codegen/codegen.go

@@ -745,6 +745,27 @@ func (g *Generator) generateSceneConstructor(comp *guixast.Component) *ast.FuncD
 
 // generateRenderSceneMethod generates the RenderScene method for a Scene component
 func (g *Generator) generateRenderSceneMethod(comp *guixast.Component) *ast.FuncDecl {
+	// Generate variable declarations first
+	var stmts []ast.Stmt
+	if comp.Body != nil && len(comp.Body.VarDecls) > 0 {
+		for _, varDecl := range comp.Body.VarDecls {
+			// Generate: varName := value
+			var lhs []ast.Expr
+			for _, name := range varDecl.Names {
+				lhs = append(lhs, ast.NewIdent(name))
+			}
+			var rhs []ast.Expr
+			for _, value := range varDecl.Values {
+				rhs = append(rhs, g.generateExpr(value))
+			}
+			stmts = append(stmts, &ast.AssignStmt{
+				Lhs: lhs,
+				Tok: token.DEFINE, // :=
+				Rhs: rhs,
+			})
+		}
+	}
+
 	// Generate scene graph from body children
 	var sceneNode ast.Expr
 	if comp.Body != nil && len(comp.Body.Children) > 0 {
@@ -760,6 +781,11 @@ func (g *Generator) generateRenderSceneMethod(comp *guixast.Component) *ast.Func
 		}
 	}
 
+	// Add return statement
+	stmts = append(stmts, &ast.ReturnStmt{
+		Results: []ast.Expr{sceneNode},
+	})
+
 	return &ast.FuncDecl{
 		Recv: &ast.FieldList{
 			List: []*ast.Field{
@@ -787,11 +813,7 @@ func (g *Generator) generateRenderSceneMethod(comp *guixast.Component) *ast.Func
 			},
 		},
 		Body: &ast.BlockStmt{
-			List: []ast.Stmt{
-				&ast.ReturnStmt{
-					Results: []ast.Expr{sceneNode},
-				},
-			},
+			List: stmts,
 		},
 	}
 }
@@ -1867,6 +1889,7 @@ var runtimeFunctions = map[string]bool{
 	"LookAtPos": true, "Background": true,
 	"Width": true, "Height": true,
 	"GeometryProp": true, "MaterialProp": true, "GPURenderUpdate": true,
+	"WithGeometry": true, "WithMaterial": true, "BindRotation": true,
 	// GPU constructors
 	"NewBoxGeometry": true, "NewSphereGeometry": true, "NewPlaneGeometry": true,
 	"StandardMaterial": true,