A directory holding only kanban.db (no board.json) is a stub, never a
board: _dir_holds_board/list_boards/board_exists now require the metadata
file, so historical DB-only ghosts stop surfacing as empty active boards
(#43243).
remove_board(archive=True) leaves an archived tombstone board.json at the
original slug so stale readers can distinguish an archived slug from a
never-created one; create_board clears the tombstone (explicit creation
wins), get_current_board falls through archived slugs, and boards switch/rm
explain the tombstone in their output.
63e5656409