CUBELinux-2
94681bbdc0
Implements the source PDF's prescribed model for directory structure: 'treat the CZYX cube as the only persistent store, with system calls that operate on CZYX records and Null-space flags rather than paths and inodes.' Nested dirs are RECONSTRUCTED from a per-record `path` metatag, so the filesystem does not need recursive inode trees. - cubecoords: add CubeHeader.path (Option<String>) + HAS_PATH flag bit (1<<8); refresh_flags() sets it. Cubestore TLV codec now serializes/deserializes the path as tag 13 (persists across checkpoint/reopen). - cubestore: scan_by_path (exact), scan_by_path_prefix (dir listing by path prefix; bare '/etc' normalized to '/etc/'), plus query_by_path/_prefix returning decoded (coord,header,body). - cubesys: `put` verb gains path=<p>; new `query-path <dir>` verb reconstructs a directory listing from metatags. - ConcurrentStore: query_by_path(_prefix) delegate to inner CubeStore. Verified live in VM: migrated /etc/passwd, /etc/network/interfaces, /usr/bin/ls at unrelated coordinates; 'query-path /etc' returns the two /etc files, '/usr/bin/ls' correctly excluded. cubestore 8/8 tests pass. Refs: OS-in-CUBE migration, query-layer prototype.