Addresses crash and clarifies errors around container commands.
- Update server.c to handle container commands with no subcommand: emit
"missing subcommand. Try HELP."; keep "unknown subcommand" for invalid
subcommands; for unknown commands, include args preview only when
present
- Add a test module command subcommands.internal_container with a
subcommand for validation
- Add unit test asserting missing subcommand error when calling the
internal container command without arguments
25f780b662