mesh-knowledge: clear a never-reviewed notice once the record moves on, key it by version and run of tries, say times locally (review of #219)

A notice left open kept telling the operator a record was proposed and not in force after it was proposed again
or accepted, and a later version's notice merged into it.

modules/mesh-knowledge/cmd/mesh-knowledge/pgstore.go

@@ -549,6 +549,29 @@ func (s *PgStore) Findings(ctx context.Context) ([]Finding, error) {
 	return out, rows.Err()
 }
 
+func (s *PgStore) ToldOf(ctx context.Context, prefix string) ([]string, error) {
+	// left() and not like: a prefix may hold an underscore, which like would take for any character.
+	rows, err := s.pool.Query(ctx, `select topic from told where left(topic, length($1)) = $1 order by topic`, prefix)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var out []string
+	for rows.Next() {
+		var k string
+		if err := rows.Scan(&k); err != nil {
+			return nil, err
+		}
+		out = append(out, k)
+	}
+	return out, rows.Err()
+}
+
+func (s *PgStore) Untold(ctx context.Context, key string) error {
+	_, err := s.pool.Exec(ctx, `delete from told where topic = $1`, key)
+	return err
+}
+
 func (s *PgStore) Told(ctx context.Context, topic string) (bool, error) {
 	tag, err := s.pool.Exec(ctx, `insert into told (topic) values ($1) on conflict do nothing`, topic)
 	if err != nil {