feat(workspace): stack hashtag back button above heading and add dedicated hashtag markdown note (#tag.md)

internal/storage/sqlite.go

@@ -249,6 +249,14 @@ func (s *Store) migrate() error {
 	CREATE INDEX IF NOT EXISTS idx_doc_block_tags_user_tag ON doc_block_tags(user_id, tag);
 	CREATE INDEX IF NOT EXISTS idx_doc_block_tags_doc ON doc_block_tags(doc_id);
 
+	CREATE TABLE IF NOT EXISTS tag_pages (
+		user_id TEXT NOT NULL,
+		tag TEXT NOT NULL,
+		content TEXT NOT NULL DEFAULT '',
+		updated_at TEXT NOT NULL,
+		PRIMARY KEY(user_id, tag)
+	);
+
 	CREATE TABLE IF NOT EXISTS lists (
 		id TEXT PRIMARY KEY,
 		space_id TEXT NOT NULL,
@@ -1577,6 +1585,41 @@ func (s *Store) indexDocBlockTags(docID, userID string, blocks []domain.Document
 	return nil
 }
 
+func (s *Store) saveTagPageToDisk(userID, tag, content string) {
+	if s.docDir == "" || tag == "" {
+		return
+	}
+	tagDir := filepath.Join(filepath.Dir(s.docDir), "tag_pages", userID)
+	_ = os.MkdirAll(tagDir, 0755)
+	safeTag := regexp.MustCompile(`[^a-zA-Z0-9äöüÄÖÜß_-]+`).ReplaceAllString(tag, "_")
+	targetPath := filepath.Join(tagDir, safeTag+".md")
+	if strings.TrimSpace(content) == "" {
+		_ = os.Remove(targetPath)
+		return
+	}
+	md := fmt.Sprintf("# #%s\n\n%s\n", tag, content)
+	_ = os.WriteFile(targetPath, []byte(md), 0644)
+}
+
+func (s *Store) UpdateTagPageNote(userID, tag, content string) (string, error) {
+	cleanTag := strings.ToLower(strings.TrimPrefix(strings.TrimSpace(tag), "#"))
+	if cleanTag == "" {
+		return "", errors.New("tag name required")
+	}
+	now := domain.NowISO()
+	_, err := s.db.Exec(
+		`INSERT INTO tag_pages (user_id, tag, content, updated_at)
+		 VALUES (?, ?, ?, ?)
+		 ON CONFLICT(user_id, tag) DO UPDATE SET content = excluded.content, updated_at = excluded.updated_at`,
+		userID, cleanTag, content, now,
+	)
+	if err != nil {
+		return "", err
+	}
+	s.saveTagPageToDisk(userID, cleanTag, content)
+	return now, nil
+}
+
 func (s *Store) GetWorkspaceTags(userID string) ([]domain.TagSummary, error) {
 	rows, err := s.db.Query(
 		`SELECT t.tag, COUNT(DISTINCT t.doc_id || ':' || t.block_id) as count
@@ -1595,12 +1638,32 @@ func (s *Store) GetWorkspaceTags(userID string) ([]domain.TagSummary, error) {
 	defer rows.Close()
 
 	results := make([]domain.TagSummary, 0)
+	seen := make(map[string]bool)
 	for rows.Next() {
 		var ts domain.TagSummary
 		if err := rows.Scan(&ts.Tag, &ts.Count); err == nil {
 			results = append(results, ts)
+			seen[ts.Tag] = true
 		}
 	}
+	_ = rows.Close()
+
+	// Also include tags that have a non-empty tag_pages note even if not currently used in a block
+	pageRows, err := s.db.Query(
+		`SELECT tag FROM tag_pages WHERE user_id = ? AND TRIM(content) != '' ORDER BY tag ASC`,
+		userID,
+	)
+	if err == nil {
+		for pageRows.Next() {
+			var t string
+			if err := pageRows.Scan(&t); err == nil && t != "" && !seen[t] {
+				results = append(results, domain.TagSummary{Tag: t, Count: 0})
+				seen[t] = true
+			}
+		}
+		_ = pageRows.Close()
+	}
+
 	return results, nil
 }
 
@@ -1610,6 +1673,12 @@ func (s *Store) GetTagDetails(userID, tag string) (*domain.TagDetails, error) {
 		return &domain.TagDetails{Tag: "", Documents: []domain.TagDocumentGroup{}, TotalMatches: 0}, nil
 	}
 
+	var noteContent, noteUpdatedAt string
+	_ = s.db.QueryRow(
+		`SELECT content, updated_at FROM tag_pages WHERE user_id = ? AND tag = ?`,
+		userID, cleanTag,
+	).Scan(&noteContent, &noteUpdatedAt)
+
 	rows, err := s.db.Query(
 		`SELECT t.block_id, d.id, d.title, d.icon, d.folder_path, d.blocks_json, d.updated_at, d.user_id,
 		        COALESCE(u.display_name, '') as owner_name,
@@ -1734,9 +1803,11 @@ func (s *Store) GetTagDetails(userID, tag string) (*domain.TagDetails, error) {
 	}
 
 	return &domain.TagDetails{
-		Tag:          cleanTag,
-		Documents:    docGroups,
-		TotalMatches: totalMatches,
+		Tag:           cleanTag,
+		NoteContent:   noteContent,
+		NoteUpdatedAt: noteUpdatedAt,
+		Documents:     docGroups,
+		TotalMatches:  totalMatches,
 	}, nil
 }