манифесты стали данными, заведён convy sync

- убраны комментарии из suite.toml и .conventions.toml: файл, который
  машина переписывает, комментарий через круг не проносит; объяснения
  ушли в README рядом, который suite init теперь заводит
- удалена текстовая правка манифеста целиком — 520 строк ручного
  лексера TOML вместе со всем классом ошибок порчи данных
- запись идёт из структур энкодером; ключ, которого инструмент не
  знает, запись останавливает, а не теряется молча
- convy sync сверяет манифест и подводит под него раскладку файлов:
  чего не хватает — собирает, что осиротело — удаляет, копию с
  локальной частью не трогает никогда

internal/manifest/manifest_test.go

@@ -0,0 +1,168 @@
+package manifest_test
+
+import (
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"git.vakhrushev.me/av/convy/internal/manifest"
+)
+
+func write(t *testing.T, dir, name, body string) string {
+	t.Helper()
+	path := filepath.Join(dir, name)
+	if err := os.WriteFile(path, []byte(body), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	return path
+}
+
+// A manifest is data, and a command that changes it rewrites it whole. The
+// second write of the same content has to come out the same, or every command
+// would leave a diff of its own on top of the one it meant.
+func TestSaveIsIdempotent(t *testing.T) {
+	dir := t.TempDir()
+	write(t, dir, manifest.Name, `[language]
+version = 1
+lang = "ru"
+
+[topics.live]
+time = "время"
+
+[prefixes.live]
+TIME = "conventions/time.md"
+`)
+
+	m, err := manifest.Load(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := m.Save(); err != nil {
+		t.Fatal(err)
+	}
+	once, err := os.ReadFile(m.Path)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	again, err := manifest.Load(dir)
+	if err != nil {
+		t.Fatalf("the manifest the tool wrote does not load: %v\n%s", err, once)
+	}
+	if err := again.Save(); err != nil {
+		t.Fatal(err)
+	}
+	twice, err := os.ReadFile(m.Path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(once) != string(twice) {
+		t.Errorf("the second write differs from the first:\n%s\n---\n%s", once, twice)
+	}
+}
+
+// A write goes out of the structs, so a key the tool does not know would be
+// dropped. It refuses instead: that neither loses the key nor hides it.
+func TestSaveRefusesWhileAKeyIsUnknown(t *testing.T) {
+	dir := t.TempDir()
+	write(t, dir, manifest.Name, `[language]
+version = 1
+descriptoin = "LANGUAGE.md"
+`)
+
+	m, err := manifest.Load(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	before, _ := os.ReadFile(m.Path)
+
+	err = m.Save()
+	if err == nil {
+		t.Fatal("the manifest was rewritten over a key the tool does not know")
+	}
+	if !strings.Contains(err.Error(), "descriptoin") {
+		t.Errorf("the refusal does not name the key: %s", err)
+	}
+	after, _ := os.ReadFile(m.Path)
+	if string(before) != string(after) {
+		t.Errorf("the file was touched anyway:\n%s", after)
+	}
+}
+
+// A name never leaves the manifest: it lives on in foreign repositories, and
+// one handed out twice starts pointing at something else there.
+func TestRetireMovesRatherThanDeletes(t *testing.T) {
+	dir := t.TempDir()
+	write(t, dir, manifest.Name, `[language]
+version = 1
+
+[topics.live]
+time = "время"
+logging = "логирование"
+`)
+
+	m, err := manifest.Load(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	m.Topics.Retire("logging", "2026-07-28: свёрнута в errors")
+	if err := m.Save(); err != nil {
+		t.Fatal(err)
+	}
+
+	back, err := manifest.Load(dir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if back.TopicLive("logging") {
+		t.Errorf("the topic stayed live")
+	}
+	if !back.TopicRetired("logging") {
+		t.Errorf("the topic is neither live nor retired: the name is loose")
+	}
+	if !back.TopicLive("time") {
+		t.Errorf("the other topic went with it")
+	}
+}
+
+func TestProjectRoundTrip(t *testing.T) {
+	dir := t.TempDir()
+	p := &manifest.Project{
+		Source: "../dev-conventions#v2",
+		Components: map[string]manifest.Component{
+			"backend": {Dir: `docs\conventions`, Lang: []string{"go"}, Topics: []string{"time"}},
+			"web":     {Dir: "web/docs", Topics: []string{}},
+		},
+		Path: filepath.Join(dir, manifest.ProjectName),
+		Root: dir,
+	}
+	if err := p.Save(); err != nil {
+		t.Fatal(err)
+	}
+
+	back, err := manifest.LoadProject(dir)
+	if err != nil {
+		t.Fatalf("the manifest the tool wrote does not load: %v", err)
+	}
+	if back.Source != p.Source {
+		t.Errorf("source came back as %q", back.Source)
+	}
+	// A backslash is the ordinary way a written value fails to read back.
+	if got := back.Components["backend"].Dir; got != `docs\conventions` {
+		t.Errorf("the directory came back as %q", got)
+	}
+	if len(back.Components["web"].Lang) != 0 {
+		t.Errorf("an empty axis was written and read back as something")
+	}
+
+	back.Subscribe("web", "logging")
+	back.Subscribe("web", "errors")
+	if got := back.Components["web"].Topics; strings.Join(got, ",") != "errors,logging" {
+		t.Errorf("the subscription is not kept in order: %v", got)
+	}
+	back.Unsubscribe("web", "errors")
+	if got := back.Components["web"].Topics; strings.Join(got, ",") != "logging" {
+		t.Errorf("unsubscribing left %v", got)
+	}
+}