feat(11.1-05): pin the walkthrough to the scaffolder and link it from the concept map

- TestScaffoldLayout runs make:plugin, make:model, make:migration,
  make:admin-controller and make:command for acme.blog in a copy of
  examples/hello and compares the file set with docs/examples/blog
- the page lists the exact make commands, the go.mod a scaffolded plugin
  gets, what the scaffolder leaves to the developer and a checklist
- scaffolding.md no longer claims same-second migrations get consecutive
  timestamps; only same-name ones do
- coming-from-wintercms.md and index.md link the walkthrough

docs/examples/blog/scaffold_layout_test.go

@@ -0,0 +1,143 @@
+package blog_test
+
+import (
+	"io/fs"
+	"os"
+	"path/filepath"
+	"regexp"
+	"slices"
+	"strings"
+	"testing"
+
+	"git.golem15.com/golem15/summercms/internal/build"
+)
+
+// TestScaffoldLayout pins the walkthrough to the scaffolder: running the
+// make commands the porting page lists for acme.blog, in its order, in a
+// copy of the examples/hello application, must produce exactly the files of
+// this plugin (without its tests, and with migration timestamps normalised). The
+// in-repository copy has no go.mod or go.sum because it lives in the
+// framework module; those two are left out of the scaffolder's set.
+func TestScaffoldLayout(t *testing.T) {
+	// The make commands run go mod tidy; keep it on the module cache.
+	t.Setenv("GOPROXY", "off")
+	root, err := filepath.Abs(filepath.Join("..", "..", ".."))
+	if err != nil {
+		t.Fatal(err)
+	}
+	app := copyApp(t, filepath.Join(root, "examples", "hello"), root)
+
+	ctx := t.Context()
+	if _, err := build.MakePlugin(ctx, app, "acme.blog"); err != nil {
+		t.Fatalf("MakePlugin: %v", err)
+	}
+	if _, err := build.MakeModel(ctx, app, "acme.blog", "Post", false); err != nil {
+		t.Fatalf("MakeModel: %v", err)
+	}
+	if _, err := build.MakeMigration(ctx, app, "acme.blog", "AddPublishedAt"); err != nil {
+		t.Fatalf("MakeMigration: %v", err)
+	}
+	if _, err := build.MakeAdminController(ctx, app, "acme.blog", "Posts"); err != nil {
+		t.Fatalf("MakeAdminController: %v", err)
+	}
+	if _, err := build.MakeCommand(ctx, app, "acme.blog", "Publish"); err != nil {
+		t.Fatalf("MakeCommand: %v", err)
+	}
+
+	scaffolded := fileSet(t, filepath.Join(app, "plugins", "blog"), func(rel string) bool {
+		return rel != "go.mod" && rel != "go.sum"
+	})
+	walkthrough := fileSet(t, ".", func(rel string) bool {
+		return !strings.HasSuffix(rel, "_test.go")
+	})
+	var missing, extra []string
+	for _, f := range scaffolded {
+		if !slices.Contains(walkthrough, f) {
+			missing = append(missing, f)
+		}
+	}
+	for _, f := range walkthrough {
+		if !slices.Contains(scaffolded, f) {
+			extra = append(extra, f)
+		}
+	}
+	if len(missing) > 0 || len(extra) > 0 {
+		t.Errorf("docs/examples/blog differs from the scaffolder output\nscaffolded but missing here: %v\nhere but not scaffolded: %v", missing, extra)
+	}
+}
+
+var migrationStamp = regexp.MustCompile(`^updates/\d{14}_`)
+
+// fileSet returns the sorted relative paths of the files under dir that keep
+// accepts, with a leading 14-digit migration timestamp replaced by a token.
+func fileSet(t *testing.T, dir string, keep func(rel string) bool) []string {
+	t.Helper()
+	var out []string
+	err := filepath.WalkDir(dir, func(p string, d fs.DirEntry, err error) error {
+		if err != nil || d.IsDir() {
+			return err
+		}
+		rel, err := filepath.Rel(dir, p)
+		if err != nil {
+			return err
+		}
+		rel = filepath.ToSlash(rel)
+		if keep(rel) {
+			out = append(out, migrationStamp.ReplaceAllString(rel, "updates/TIMESTAMP_"))
+		}
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	slices.Sort(out)
+	return out
+}
+
+// copyApp copies the application at src into a temporary directory, without
+// its bin/ directory, and points every go.mod replace of the framework
+// module at framework.
+func copyApp(t *testing.T, src, framework string) string {
+	t.Helper()
+	const module = "git.golem15.com/golem15/summercms"
+	dst := t.TempDir()
+	err := filepath.WalkDir(src, func(p string, d fs.DirEntry, err error) error {
+		if err != nil {
+			return err
+		}
+		rel, err := filepath.Rel(src, p)
+		if err != nil {
+			return err
+		}
+		if d.IsDir() {
+			if rel == "bin" {
+				return filepath.SkipDir
+			}
+			return os.MkdirAll(filepath.Join(dst, rel), 0o755)
+		}
+		data, err := os.ReadFile(p)
+		if err != nil {
+			return err
+		}
+		if d.Name() == "go.mod" {
+			lines := strings.Split(string(data), "\n")
+			for i, line := range lines {
+				trimmed := strings.TrimSpace(strings.TrimPrefix(strings.TrimSpace(line), "replace "))
+				if strings.HasPrefix(trimmed, module+" =>") {
+					indent := line[:len(line)-len(strings.TrimLeft(line, " \t"))]
+					prefix := ""
+					if strings.HasPrefix(strings.TrimSpace(line), "replace ") {
+						prefix = "replace "
+					}
+					lines[i] = indent + prefix + module + " => " + framework
+				}
+			}
+			data = []byte(strings.Join(lines, "\n"))
+		}
+		return os.WriteFile(filepath.Join(dst, rel), data, 0o644)
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	return dst
+}