feat(desktop): add keep awake while agents are active setting

[wesbillman]

Summary

• Adds a "Keep awake while agents are active" toggle to Settings > Agents that holds a macOS PreventUserIdleSystemSleep IOKit power assertion while local managed agents are running
• Safety rails: auto-release when agents stop, 4-hour hard cap with user notification, cleanup on app exit
• Toggle defaults to OFF; no-op on non-macOS platforms

Implementation

Rust backend (prevent_sleep.rs): Raw IOKit FFI — IOPMAssertionCreateWithName / IOPMAssertionRelease behind #[cfg(target_os = "macos")]. State managed via Arc<Mutex<PreventSleepState>>. 4-hour timer auto-releases and emits a Tauri event.

Frontend (usePreventSleep.ts): React context provider (single source of truth) watches managed agent status and syncs to backend. Settings card consumes context — no dual-hook race.

Safety design:

• PreventUserIdleSystemSleep (not display sleep) — only prevents idle sleep, lid-close/critical-battery/manual sleep still work
• Assertion tied to status === "running" agents only (not "deployed" remote agents)
• 4-hour hard cap: timer calls release() then emits frontend notification
• RunEvent::Exit handler releases before shutdown_managed_agents
• CFString null checks in unsafe block

Files changed (11)

• 4 new: prevent_sleep.rs, commands/prevent_sleep.rs, usePreventSleep.ts, PreventSleepSettingsCard.tsx
• 7 modified: app_state.rs, commands/mod.rs, lib.rs, AppShell.tsx, SettingsPanels.tsx, tauri.ts, check-file-sizes.mjs

Test plan

• Toggle ON with no agents running → status shows "Waiting for agents to start", pmset -g assertions shows no Sprout assertion
• Start a local agent → status shows "Active", pmset -g assertions shows PreventUserIdleSystemSleep by Sprout
• Stop all agents → assertion auto-releases, status shows "Inactive"
• Toggle OFF while agents running → assertion releases immediately
• Wait 4 hours (or reduce CAP_SECONDS for testing) → assertion releases, expiry banner appears
• Quit app while assertion held → assertion released (verify via pmset -g assertions)
• Settings toggle persists across app restart (localStorage)

🤖 Generated with Claude Code