suite check: закрыты пробелы в проверках шапки, иерархии и словаря

- документ без темы: ошибка, если такой не один или если он несёт ключи слоя —
  иначе конвенция, потерявшая topic, молча лишалась всех проверок распространения
- иерархия заголовков: один заголовок первого уровня, без перескоков через уровень
- имя темы: латиница и пригодность для имени файла — ошибкой, kebab-case —
  предупреждением
- сценарные связки чужого словаря ловятся в начале строки, где их ставит
  сценарный блок, а не в середине фразы, где это чаще SQL

internal/check/suite.go

@@ -1,6 +1,7 @@
 package check
 
 import (
+	"regexp"
 	"sort"
 
 	"git.vakhrushev.me/av/convy/internal/manifest"
@@ -11,7 +12,9 @@ import (
 func Suite(s *suite.Suite) *Report {
 	rep := &Report{}
 	checkManifest(s, rep)
+	checkTopicNames(s, rep)
 	checkBaseLayers(s, rep)
+	checkSelfGoverning(s, rep)
 
 	for _, d := range s.Docs {
 		checkForm(s, d, rep)
@@ -87,6 +90,64 @@ func checkManifest(s *suite.Suite, rep *Report) {
 	}
 }
 
+var (
+	// topicNameRe is the hard bound: a topic name reaches the file system of
+	// a consumer, so it has to be usable as a file name — Latin letters,
+	// digits and the plain separators.
+	topicNameRe = regexp.MustCompile(`^[A-Za-z0-9][A-Za-z0-9._-]*$`)
+	// kebabRe is the recommended shape, and only a recommendation.
+	kebabRe = regexp.MustCompile(`^[a-z0-9]+(-[a-z0-9]+)*$`)
+)
+
+// checkTopicNames checks the shape of topic names. A name lands both in a
+// consumer's file system and in their manifest, which is where the hard bound
+// comes from; lower kebab-case on top of that is a recommendation and speaks as
+// a warning.
+func checkTopicNames(s *suite.Suite, rep *Report) {
+	for _, topic := range s.Manifest.LiveTopics() {
+		switch {
+		case !topicNameRe.MatchString(topic):
+			rep.Errorf(Manifest, manifest.Name, 0,
+				"the topic name %q is not usable as a file name: a name is written in Latin letters and travels into the file system of a consumer", topic)
+		case !kebabRe.MatchString(topic):
+			rep.Warnf(Manifest, manifest.Name, 0,
+				"the topic name %q is not lower kebab-case, which is the recommended shape", topic)
+		}
+	}
+}
+
+// checkSelfGoverning guards the document without a topic.
+//
+// A topic-less document is the one the suite governs itself by: it travels
+// nowhere and cannot be subscribed to, so it gets no spread checks. Nothing in
+// the manifest tells it from a convention that lost its topic key, and the
+// silent loss is the expensive one — the file keeps every check of form while
+// quietly dropping every check about travelling to a consumer. Two markers make
+// that loss visible: such a document is one per suite, and it has no layer of
+// its own, hence neither axis keys nor a base.
+func checkSelfGoverning(s *suite.Suite, rep *Report) {
+	var topicless []string
+	for _, d := range s.Docs {
+		if d.Front.Topic != "" {
+			continue
+		}
+		topicless = append(topicless, d.Path)
+
+		if d.Front.Axis() || d.Front.Extends != "" {
+			rep.Errorf(Manifest, d.Path, d.Front.At["prefix"],
+				"the file declares no topic yet carries the keys of a layer: a document without a topic is the one the suite governs itself by, and it is nobody's layer — the topic key looks lost")
+		}
+	}
+	if len(topicless) > 1 {
+		sort.Strings(topicless)
+		for _, path := range topicless[1:] {
+			rep.Errorf(Manifest, path, 1,
+				"the suite holds more than one document without a topic (%v): only the one the suite governs itself by may lack a topic, so the rest have lost the key",
+				topicless)
+		}
+	}
+}
+
 // checkBaseLayers checks that a topic holds no more than one layer without axis
 // keys. The base layer is the only one of its kind: it reaches every copy, and a
 // second such layer would mean two base texts in one assembled file.