CUBELinux-2
cf10cfcf51
TenantConfig::Disk opens each tenant's ConcurrentStore under its own
sanitized subdir of store_dir (path separators -> '_', no traversal escape),
reusing the durable WAL+checkpoint machinery (incl. 49698af delta-path fix).
Registry takes a config; get_or_provision returns io::Result so a disk
open failure surfaces instead of silently falling back to memory.
Tests: tenant_store_is_isolated_on_disk (separate dirs + survives reopen,
B still isolated) + tenant_id_cannot_traverse_store_dir. ./check green.