The placeholder promised less than the user wanted and the matcher
delivered less than the placeholder should: the search box only
substring-matched title and directory. It now also matches the
session's newest own message (timeline.lastUser, the card preview
text), case-insensitively, and a non-string fold shape safely never
matches. The placeholder copy follows in both locales ("Search title /
path / last message..." / "搜索标题 / 目录 / 最后消息...").