[Copilot]

Cobra parses --flag "" into an empty slice. This is indistinguishable from the flag being omitted, but it passes the MarkFlagRequired check. Commands that loop over such a flag silently do nothing, or send a request with an empty list, instead of failing.

$ neofs-cli object lock --cid <cid> --oid '' --lifetime 100 -r localhost:8080
# before: continues and fails later with "container not found"
# after:  Error: provide at least one object via oid flag

Each of the commands below now fails fast with "provide at least one … via -- flag" when the parsed slice has no elements:

• neofs-cli object lock: the --oid flag.
• neofs-cli control drop-objects: the --objects flag.
• neofs-adm fschain: container IDs flag, checked in getCIDs.
• neofs-lancet fstree and meta remove: the --addresses flag.

object delete already had this check, so it is unchanged.

Not covered: other slice flags (shard IDs, attributes, search filters, session subjects, X-headers) are untouched. Their empty value is either a valid input or not clearly a bug. Say if you want them checked too.

• Fixes Check that all Cobra commands check length slice flags for emptiness if required #2879