parseSlashSeparatedArg convention

Always parse [<org>/<project>/]<id> positionals with parseSlashSeparatedArg; IDs such as event, trace, and log hex IDs never contain /. A slash therefore denotes structured target syntax: one slash is an incomplete org/project target missing its ID, while 2+ slashes split at the final slash. Plain no-slash IDs intentionally bypass generic validation because callers may preprocess them; format-specific validators must run downstream.