You opened Shelley on your phone.
Your Mac had gone to sleep.

Why your Mac sleeps while Shelley is still working

Shelley, from Bold Software, is a web-based coding agent: a single binary you run on your own machine that serves a browser UI, stores conversations in SQLite, and streams updates to whatever device you have open. The team's stated reason for the single-user design is that it makes sense to "bring the agent to the compute" — and on a Mac, the compute is a laptop that sleeps.

macOS decides to idle-sleep from your idle time — how long since real keyboard or mouse input — and from the sleep assertions running processes hold. CPU load is not part of that decision, which surprises people: a Mac pinned at 100% still idle-sleeps on schedule. So an agent that's working hard doesn't protect itself, and driving that agent from a phone produces no input on the Mac at all. When the idle timer runs out, the machine suspends. The shelley process isn't killed — it's frozen with everything else, the SSE connection your browser was holding drops, and the turn that was in flight goes nowhere until you go back and wake the Mac up.

Two things make this sting more with Shelley than with a terminal agent. First, the pitch is specifically that you can start work from anywhere — the times you'd use that are the times the Mac is unattended. Second, if the way you leave the desk is closing the lid, that's a separate and harder problem: closing the lid doesn't consult the idle timer at all, it just sleeps. The supported way around that one is clamshell mode — on power, with an external display and an external keyboard or mouse connected.

If you run Shelley now and then, you don't need to buy anything. Everything here ships with macOS or is free:

• Wrap the server in caffeinate. Whatever command you use to start Shelley, put caffeinate -i in front of it — caffeinate -i shelley. The Mac can't idle-sleep for as long as the server runs, and normal sleep comes back by itself the moment it exits. Nothing to remember to undo.
• Attach to a server that's already up. You don't have to restart it: caffeinate -i -w $(pgrep -n shelley) holds sleep off until that specific process ends. Check what you'd be attaching to first with pgrep -l shelley — if nothing matches, caffeinate just prints a usage error, and if you built from source or renamed the binary, confirm the name before trusting the match.
• Amphetamine (free, Mac App Store) if you'd rather flip a menu-bar switch than type a command. Keeps the Mac awake on a timer or while a chosen app is running.
• Free agent-aware tools exist too. Keepresso (free, GPL-3.0) and adrafinil (free, MIT) detect when an agent's turn starts and ends by hooking into the agent itself rather than guessing from CPU — for the agents they support, that's more accurate than any heuristic, ours included. Worth knowing before you pay anyone, including us.

The honest catch with a bare caffeinate, and it's bigger for a server-shaped agent than a terminal one: it doesn't know the difference between working and waiting. A one-shot command exits when it's done, so caffeinate -i claude -p "…" releases itself — but an interactive session sitting at its prompt holds sleep off just as long as a server does, and a Shelley server stays up for hours after your last turn finished. Wrapping it means your Mac simply never idle-sleeps while the server is running, and on battery that is how people come back to 0%. You can stop it yourself when you remember, or you can have something watch for actual work.