feat(04-01): scaffold Winter-shaped plugins with generated registry

Render plugin.go, routes.go, leaf packages and go.mod from embedded
templates, emit empty registry accessors, and define job, admin, lang
and mail capability contracts so a new plugin compiles before artifacts.

Co-authored-by: Cursor <cursoragent@cursor.com>

internal/build/scaffold.go

@@ -3,6 +3,7 @@ package build
 import (
 	"bytes"
 	"context"
+	"embed"
 	"fmt"
 	"go/ast"
 	"go/format"
@@ -13,8 +14,34 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"text/template"
 )
 
+//go:embed stubs/*.tmpl
+var stubFS embed.FS
+
+var stubTmpl = template.Must(template.ParseFS(stubFS, "stubs/*.tmpl"))
+
+var pluginLeaves = []string{
+	"models",
+	"classes",
+	"controllers",
+	"console",
+	"jobs",
+	"middleware",
+	"updates",
+}
+
+type stubData struct {
+	Package   string
+	ID        string
+	Module    string
+	Framework string
+	GoVersion string
+	Toolchain string
+	Replace   string
+}
+
 const (
 	frameworkModule = "git.golem15.com/golem15/summercms"
 	goVersionLine   = "go 1.27.0"
@@ -50,27 +77,21 @@ func MakePlugin(ctx context.Context, startDir, id string) (string, error) {
 		return "", fmt.Errorf("build: plugin module: %w", err)
 	}
 
-	if err := os.MkdirAll(filepath.Join(pluginDir, "config"), 0o755); err != nil {
-		return "", fmt.Errorf("build: create plugin dir: %w", err)
-	}
-	if err := os.WriteFile(filepath.Join(pluginDir, "config", ".gitkeep"), []byte{}, 0o644); err != nil {
-		return "", fmt.Errorf("build: write config placeholder: %w", err)
-	}
-
-	src, err := pluginGoSource(name, id)
-	if err != nil {
-		return "", err
-	}
-	if err := os.WriteFile(filepath.Join(pluginDir, "plugin.go"), src, 0o644); err != nil {
-		return "", fmt.Errorf("build: write plugin.go: %w", err)
-	}
-
 	replace, err := frameworkReplaceFor(pluginDir, appDir)
 	if err != nil {
 		return "", err
 	}
-	if err := os.WriteFile(filepath.Join(pluginDir, "go.mod"), pluginGoMod(modPath, replace), 0o644); err != nil {
-		return "", fmt.Errorf("build: write go.mod: %w", err)
+	data := stubData{
+		Package:   name,
+		ID:        id,
+		Module:    modPath,
+		Framework: frameworkModule,
+		GoVersion: goVersionLine,
+		Toolchain: toolchainLine,
+		Replace:   replace,
+	}
+	if err := writePluginScaffold(pluginDir, data); err != nil {
+		return "", err
 	}
 	if err := runGo(ctx, pluginDir, "mod", "tidy"); err != nil {
 		return "", err
@@ -156,39 +177,83 @@ func pluginName(id string) string {
 	return name
 }
 
-func pluginGoSource(pkg, id string) ([]byte, error) {
-	var b strings.Builder
-	b.WriteString("package " + pkg + "\n\n")
-	b.WriteString("import (\n")
-	b.WriteString("\t\"git.golem15.com/golem15/summercms/backpack\"\n")
-	b.WriteString("\t\"git.golem15.com/golem15/summercms/party\"\n")
-	b.WriteString(")\n\n")
-	fmt.Fprintf(&b, "// Plugin is the %s plugin.\n", id)
-	b.WriteString("type Plugin struct{}\n\n")
-	fmt.Fprintf(&b, "func (p *Plugin) ID() string         { return %s }\n", strconv.Quote(id))
-	b.WriteString("func (p *Plugin) Requires() []string { return nil }\n\n")
-	b.WriteString("func (p *Plugin) Register(*backpack.App) error { return nil }\n")
-	b.WriteString("func (p *Plugin) Boot(*backpack.App) error     { return nil }\n\n")
-	b.WriteString("func init() {\n")
-	b.WriteString("\tparty.Register(&Plugin{})\n")
-	b.WriteString("}\n")
-	formatted, err := format.Source([]byte(b.String()))
+func writePluginScaffold(pluginDir string, data stubData) error {
+	if err := os.MkdirAll(pluginDir, 0o755); err != nil {
+		return fmt.Errorf("build: create plugin dir: %w", err)
+	}
+	pluginSrc, err := renderStub("plugin.go", data)
 	if err != nil {
-		return nil, fmt.Errorf("build: format plugin.go: %w", err)
+		return err
+	}
+	if err := writeFile(filepath.Join(pluginDir, "plugin.go"), pluginSrc); err != nil {
+		return err
+	}
+	routesSrc, err := renderStub("routes.go", data)
+	if err != nil {
+		return err
+	}
+	if err := writeFile(filepath.Join(pluginDir, "routes.go"), routesSrc); err != nil {
+		return err
+	}
+	for _, leaf := range pluginLeaves {
+		src, err := renderStub(leaf+"/doc.go", data)
+		if err != nil {
+			return err
+		}
+		if err := writeFile(filepath.Join(pluginDir, leaf, "doc.go"), src); err != nil {
+			return err
+		}
+	}
+	for _, asset := range pluginAssets {
+		if err := writeFile(filepath.Join(pluginDir, filepath.FromSlash(asset.rel)), []byte(asset.body)); err != nil {
+			return err
+		}
+	}
+	if err := writeRegistry(pluginDir, emptyRegistry(data.Package, data.Module)); err != nil {
+		return err
+	}
+	modSrc, err := renderStub("go.mod", data)
+	if err != nil {
+		return err
+	}
+	return writeFile(filepath.Join(pluginDir, "go.mod"), modSrc)
+}
+
+type pluginAsset struct {
+	rel  string
+	body string
+}
+
+var pluginAssets = []pluginAsset{
+	{rel: "config/config.yaml", body: "{}\n"},
+	{rel: "lang/en/lang.yaml", body: "{}\n"},
+	{rel: "views/mail/welcome.htm", body: "subject = \"Welcome\"\ndescription = \"Placeholder mail template\"\n==\nHello.\n"},
+}
+
+func renderStub(name string, data any) ([]byte, error) {
+	var buf bytes.Buffer
+	if err := stubTmpl.ExecuteTemplate(&buf, name, data); err != nil {
+		return nil, fmt.Errorf("build: render stub %s: %w", name, err)
+	}
+	raw := buf.Bytes()
+	if !strings.HasSuffix(name, ".go") {
+		return raw, nil
+	}
+	formatted, err := format.Source(raw)
+	if err != nil {
+		return nil, fmt.Errorf("build: format stub %s: %w\n%s", name, err, raw)
 	}
 	return formatted, nil
 }
 
-func pluginGoMod(modPath, replace string) []byte {
-	var b strings.Builder
-	fmt.Fprintf(&b, "module %s\n\n", modPath)
-	b.WriteString(goVersionLine + "\n\n")
-	b.WriteString(toolchainLine + "\n\n")
-	fmt.Fprintf(&b, "require %s v0.0.0\n", frameworkModule)
-	if replace != "" {
-		fmt.Fprintf(&b, "\nreplace %s => %s\n", frameworkModule, replace)
+func writeFile(path string, data []byte) error {
+	if err := os.MkdirAll(filepath.Dir(path), 0o755); err != nil {
+		return fmt.Errorf("build: mkdir %s: %w", filepath.Dir(path), err)
 	}
-	return []byte(b.String())
+	if err := os.WriteFile(path, data, 0o644); err != nil {
+		return fmt.Errorf("build: write %s: %w", path, err)
+	}
+	return nil
 }
 
 func frameworkReplaceFor(pluginDir, appDir string) (string, error) {