Port already in use — without lsof
Port 3000 is already in use is not a mystery. Something on this Mac bound it. The mystery is which tab, which yesterday, which Docker leftover. Rig treats ports as part of the project, not as folklore you re-learn with lsof -i :3000.
When a process in Rig claims a port, the board shows it. When something else stole it, Attention says so. You reclaim or you attach. You do not grep ps unless you enjoy it.
Why this belongs in the control plane
A local control plane that does not know ports is just a prettier Procfile. The crash you care about is often "the UI is on the wrong port" or "Vite lost to a zombie Node." Logs without ports are half a story. MCP without who_owns_port makes the agent guess too.
What we still will not do
We will not scan every socket on the machine and kill strangers for sport. Rig cares about the projects you added. If you ran a one-off server in a random tab, say so with the usual tools. The product is for the stack you boot every morning.
Related
Common port conflicts, Ports and crashes, One-click fixes. If your real problem is six tabs, read Rig vs terminal tabs.