Claude Code (subscription) has Agent Teams built in. Teams of Agents communicate with local files that they use as inboxes and task list. Has tmux and iTerm 2 integration. https://code.claude.com/docs/en/agent-teams

They can rack up some extra tokens if you leave agents going idle. Because they loop, checking for new messages for them.

This fellow reverse-engineered exactly how it works and then abstracted the pattern into an MCP server that any Harness/agent can use. https://github.com/cs50victor/claude-code-teams-mcp