Replaces the per-client stale/visibility policy with one shared
presence cascade so a backgrounded Firefox tab can no longer steal
in-app notifications from an active Electron desktop window.
Server (`agent-attention-policy.ts`): exports `PRESENCE_THRESHOLD_MS`
(3 min) and `computeNotificationPlan({ allStates, agentId, reason,
nowMs })` returning `{ inAppRecipientIndex, shouldPush }`. Cascade:
focus suppression requires presence; otherwise the most-recent
present client wins (lower-index tiebreak); push fires only when no
client is present, and never on `error`. `broadcastAgentAttention`
calls the policy once per event.
Electron (`daemon-manager.ts`, `idle.ts`): registers
`desktop_get_system_idle_time` returning `powerMonitor
.getSystemIdleTime() * 1000`. Renderer wrapper
`getDesktopSystemIdleTimeMs()` is best-effort: rejected IPC, null,
NaN, Infinity, or negative values return null without throwing.
Hook (`use-client-activity.ts`): Electron-only effect polls every 5s
and updates `lastActivityAtRef` only forward, so OS-wide activity
keeps a backgrounded Electron window present while in-window events
still update immediately.
`ClientHeartbeatMessageSchema` is unchanged; old/new clients and
daemons remain wire-compatible.
Tests: 52 focused tests across policy unit, dispatch, e2e, hook,
desktop wrapper, and permissions. Phase-3 dispatch test +
Phase-5 stale-poll test verified by mutation (breaking the focus
check / the `>` guard makes the exact regression fail).
Add `packages/app/src/constants/platform.ts` with canonical gates
(isWeb, isNative, getIsElectron) and refactor all ~100 ad-hoc
Platform.OS checks across 69 files to use shared imports.
Fix sidebar hover crash on native (onPointerEnter → onHoverIn),
fix tooltip to use breakpoint instead of platform detection, make
sidebar action buttons always visible on native where hover doesn't
work, and document the platform gating decision matrix in CLAUDE.md.
Mohamed Boudra