Add layout components 0001-0025

Stack through StickyHeader, with behavior tests and gallery demos.
kit gains Arrive, Settle (paint-time layout check) and Shade.
Several actions return named ui.Element results; mygo vet forbids
elements in structs.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

internal/archtest/arch_test.go

@@ -116,8 +116,13 @@ func TestRulesCatch(t *testing.T) {
 		{"directive", "", "package x\n// Files.\n//go:generate echo\n", comments, 0},
 		{"good", "button/icon_button.go", head + "func IconButton(c *ui.Context, o IconButtonOptions) ui.Element\n" +
 			"type IconButtonOptions struct{}\n", components, 0},
-		{"result", "button/split.go", head + "func Split(c *ui.Context) SplitResult\ntype SplitResult struct{}\n",
-			components, 0},
+		{"parts", "button/split.go", head + "func Split(c *ui.Context) (root, menu ui.Element)\n", components, 0},
+		{"struct result", "button/split.go", head + "func Split(c *ui.Context) SplitResult\ntype SplitResult struct{}\n",
+			components, 1},
+		{"unnamed parts", "button/split.go", head + "func Split(c *ui.Context) (ui.Element, ui.Element)\n",
+			components, 1},
+		{"root not first", "button/split.go", head + "func Split(c *ui.Context) (menu, root ui.Element)\n",
+			components, 1},
 		{"two", "button/a.go", head + "func A(c *ui.Context) ui.Element\nfunc B(c *ui.Context) ui.Element\n",
 			components, 1},
 		{"file name", "button/b.go", head + "func KPIGrid(c *ui.Context) ui.Element\n", components, 1},
@@ -127,6 +132,10 @@ func TestRulesCatch(t *testing.T) {
 			components, 1},
 		{"returns", "button/a.go", head + "func A(c *ui.Context) int\n", components, 1},
 		{"ctx name", "button/a.go", head + "func A(ctx *ui.Context) ui.Element\n", components, 1},
+		{"content after options", "button/a.go", head + "func A(c *ui.Context, o AOptions, content func()) ui.Element\n",
+			components, 0},
+		{"two after options", "button/a.go", head + "func A(c *ui.Context, o AOptions, a, b func()) ui.Element\n",
+			components, 1},
 		{"grouped options", "button/a.go", head + "func A(c *ui.Context, x, y AOptions) ui.Element\n",
 			components, 1},
 	}

internal/archtest/rules_test.go

@@ -107,21 +107,29 @@ func signature(fn *ast.FuncDecl) string {
 		ps[0].Names[0].Name != "c" {
 		return "must take c *ui.Context first"
 	}
+	last := ps[len(ps)-1]
+	contentLast := typeString(last.Type) == "func()" && len(last.Names) == 1
 	for i, p := range ps {
 		ts := typeString(p.Type)
 		if _, ok := p.Type.(*ast.Ellipsis); ok {
 			return "must not be variadic"
 		}
-		if strings.HasSuffix(ts, "Options") && (ts != name+"Options" || i != len(ps)-1 || len(p.Names) > 1) {
+		if strings.HasSuffix(ts, "Options") && (ts != name+"Options" || i != len(ps)-1 && !(i == len(ps)-2 && contentLast) ||
+			len(p.Names) > 1) {
 			return "options must be a final " + name + "Options"
 		}
 	}
 	rs := fn.Type.Results
-	if rs == nil || rs.NumFields() != 1 {
-		return "must return one value"
+	if rs == nil || rs.NumFields() == 0 {
+		return "must return ui.Element"
 	}
-	if r := typeString(rs.List[0].Type); r != "ui.Element" && r != name+"Result" {
-		return "must return ui.Element or " + name + "Result"
+	for _, r := range rs.List {
+		if typeString(r.Type) != "ui.Element" {
+			return "must return only ui.Element results"
+		}
+	}
+	if rs.NumFields() > 1 && (len(rs.List[0].Names) == 0 || rs.List[0].Names[0].Name != "root") {
+		return "several results must be named, root first"
 	}
 	return ""
 }
@@ -134,6 +142,10 @@ func typeString(e ast.Expr) string {
 		return "*" + typeString(t.X)
 	case *ast.SelectorExpr:
 		return typeString(t.X) + "." + t.Sel.Name
+	case *ast.FuncType:
+		if t.Params.NumFields() == 0 && t.Results.NumFields() == 0 {
+			return "func()"
+		}
 	}
 	return fmt.Sprintf("%T", e)
 }