* shell: warn in volume.list when a volume id spans collections
A reused volume id, the result of the master handing out an id already
used by another collection (for example after losing its max-volume-id
counter on restart), makes collection.delete destroy the wrong
collection's data and makes any bare-id lookup, move, or vacuum
ambiguous. volume.list now scans the full topology and warns on ids
present in more than one collection so the clash is visible before any
destructive operation.
* volume.list: track duplicate ids lazily, sort with slices.Sort
Allocate the per-id collection set only on the first cross-collection clash
instead of one set per volume, so allocations scale with duplicates rather
than the volume count.
Chris Lu
fdfeb4063c