Aider was still working.
Your Mac didn't care.

Why your Mac sleeps while Aider is still going

Aider spends most of a task waiting on a model response — which barely uses any CPU. But macOS doesn't decide from CPU at all — it goes by your idle time, how long since real keyboard or mouse input, plus the power assertions running processes hold. So working hard doesn't protect the machine: a Mac mid-refactor sleeps on exactly the same schedule as one doing nothing. After your screen-sleep or system-sleep timer runs out, macOS suspends the Mac, and the aider process is frozen along with everything else until you wake it back up.

This bites hardest on exactly the runs worth walking away from: a big multi-file edit across a repo map, an architect-plus-editor pass where two model calls happen back to back, or a long --yes-always session you kicked off and left alone. The fix is to stop macOS from sleeping for as long as the agent is actually running — then let it sleep normally again once the run is done. You can do that for free in two minutes, or with a tool that watches for real agent activity so you don't have to babysit it.

If you only run Aider occasionally, you don't need to buy anything. Because Aider is a terminal agent, the cleanest free fix is one command:

• The built-in caffeinate command. Launch your session as caffeinate -i aider instead of aider. The Mac can't idle-sleep while the agent runs, and the moment Aider exits, normal sleep is allowed again — nothing to remember to undo. Already on your Mac, free. For a scripted or unattended run, wrap the whole command the same way: caffeinate -i aider --message "your instruction" --yes-always.
• Tie it to a session that's already running. If you started Aider before you thought about sleep, you don't have to restart it — caffeinate -i -w $(pgrep -nf aider) attaches to the newest process whose command line mentions Aider and releases the moment that process exits. Use -f here rather than a plain pgrep -n aider: Aider runs as a Python program, so its own name often isn't what macOS lists as the process. Check what you'd be attaching to first with pgrep -lf aider.
• Amphetamine (free, Mac App Store). A menu-bar toggle to keep the Mac awake on a timer or while your terminal app is open — handy if you'd rather flip a switch than type a command.

All of these are a fine choice if Aider runs for a few minutes here and there. The catch: none of them knows when the agent actually finished a task versus when it's just sitting at an idle prompt. You either stop it yourself, or it keeps your Mac awake — and your battery draining — long after the work is done.