> What's useful about Herdr compared to tmux and claude code or codex's built in sub-agents?

Agent status detection. Single view over local and remote agents. /herdr skill that lets agents list other agents, peek into their panes, send keys (yes, you can make a lot of it work with tmux and some elbow grease, but herdr provides nice cli/api for it and works out of the box) including to remote ones.

In my mental model, subagents are also different from top level agents in tabs: subagents are only great as temporary workers you never want to interact with.