`backgroundInactivityTimeout` miscounts on Android due to a clock that pauses in deep sleep

[Sabaev]

1) backgroundInactivityTimeout miscounts on Android due to a clock that pauses in deep sleep

Component(s): android-agent, android, SessionManager, SessionConfig
Environment: Android (device enters Doze / deep sleep)

Summary

backgroundInactivityTimeout in SessionConfig behaves incorrectly on Android when devices enter deep sleep. The default Clock uses System.nanoTime() which maps to a monotonic source that does not advance during deep sleep. Background duration is undercounted, so sessions may not rotate when they should.

Expected behavior

Background inactivity should be measured against a time base that continues through device sleep so a configured timeout triggers after the intended real elapsed duration.

Actual behavior

When the app is backgrounded and the device sleeps, System.nanoTime() stops. On resume, SessionIdTimeoutHandler/SessionManager see a shorter elapsed interval than real time, preventing or delaying session rotation.

Why this happens (Android specifics)

• System.nanoTime() ≈ CLOCK_MONOTONIC → pauses during deep sleep.
• SystemClock.elapsedRealtime() / elapsedRealtimeNanos() → includes deep sleep; correct for elapsed-wall semantics.

Minimal reproduction

1. Set backgroundInactivityTimeout to a small value (e.g., 5 min).
2. Background the app; allow the device to enter deep sleep > timeout.
3. Resume the app.
4. Observe that the session did not rotate as expected.

Proposed change

1. Provide an Android-aware Clock that uses SystemClock.elapsedRealtimeNanos() for elapsed measurements.
2. Pass this Clock to SessionManager and SessionIdTimeoutHandler during init.
3. Remove the secondary SessionManager constructor (marked “for tests”) and add a factory method to ensure consistent wiring in prod/tests.

[Sabaev]

related to #1364