Comments used to be limited to 255 characters, a value that is hard-coded into multiple automatic edit summary truncation systems. Instead of relying on 225 (or not including a limit at all until the comment is actually saved), CommentStore::COMMENT_CHARACTER_LIMIT should be called instead.
Original proposal:
Could someone please add a global variable (eg $wgTruncatedCommentLength) for specifying the length that long summaries or auto-summaries are truncated to? There's three places in Article.php where this is done in the functions getBlankingAutosummary(), getAutosummary() and the end of delete().