Agent change needs a reason

An agent submitted cmd.apply without a nonempty why. The host dry-runs the batch to report other problems, then rejects it without committing changes, so the future reviewer is not left with an unexplained edit.

#Common causes

• The request omitted why or supplied only whitespace.
• The CLI detected an agent identity from its environment, but the command omitted --why.

#Fixes

• Retry ara do <command> --why "<reason for the change>", or add a meaningful sentence in ara_apply's why field.

• Fix any additional diagnostics returned with the dry run before resubmitting the batch.

• Code: ARA1610

• Constant: MISSING_WHY

• Reported by: ara-host