[No QA] fix: move AppStartTime recording from MainApplication to MainActivity

[war-in]

Explanation of Change

On Android, when the app is closed and quickly reopened, the system reuses the still-alive process. Since MainApplication.onCreate() only runs once per process — not on each app reopen — the startup timestamp stored in SharedPreferences becomes stale, causing the ManualAppStartup Sentry span duration to grow with each close+reopen cycle.

This PR moves the System.currentTimeMillis() recording from MainApplication.onCreate() to MainActivity.onCreate(). The Activity is recreated on every app open (even with process reuse), so the timestamp is always fresh.

Fixed Issues

$ #86474
PROPOSAL:

Tests

1. Build and run the standalone Android app
2. Open the app and observe the ManualAppStartup span duration in Sentry debug logs
3. Close the app (swipe away or press back)
4. Quickly reopen the app
5. Verify the ManualAppStartup duration is similar to step 2 (not growing)
6. Repeat close+reopen several times — duration should stay consistent

Offline tests

QA Steps

PR Author Checklist

• I linked the correct issue in the ### Fixed Issues section above
• I wrote clear testing steps that cover the changes made in this PR
  • I added steps for local testing in the Tests section
  • I added steps for the expected offline behavior in the Offline steps section
  • I added steps for Staging and/or Production testing in the QA steps section
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  • I turned off my network connection and tested it while offline to ensure it matches the expected behavior (i.e. verify the default avatar icon is displayed if app is offline)
  • I tested this PR with a High Traffic account against the staging or production API to ensure there are no regressions (e.g. long loading states that impact usability).
• I included screenshots or videos for tests on all platforms
• I ran the tests on all platforms & verified they passed on:
  • Android: Native
  • Android: mWeb Chrome
  • iOS: Native
  • iOS: mWeb Safari
  • MacOS: Chrome / Safari
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Screenshots/Videos

Android: Native

Android: mWeb Chrome

iOS: Native

iOS: mWeb Safari

MacOS: Chrome / Safari

[github-actions]

⚠️ This PR is possibly changing native code and/or updating libraries, it may cause problems with HybridApp. Please check if any patch updates are required in the HybridApp repo and run an AdHoc build to verify that HybridApp will not break. Ask Contributor Plus for help if you are not sure how to handle this. ⚠️

[melvin-bot]

@mananjadhav Please copy/paste the Reviewer Checklist from here into a new comment on this PR and complete it. If you have the K2 extension, you can simply click: [this button]

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[chatgpt-codex-connector]

Preserve app-start timestamp for headless JS launches

Writing AppStartTime only in MainActivity.onCreate() drops the update path for Android headless/background JS startups, which are documented in src/setup/index.ts (telemetry runs even when no Activity exists). In that path, AppStartTimeNitroModule.appStartTime can now come from a previous foreground session, so when ManualAppStartup is started from telemetry during early startup states (where app state may be undefined/active), durations can be inflated by long idle gaps and skew production startup metrics.

Useful? React with 👍 / 👎.

[Julesssss]

In that path, AppStartTimeNitroModule.appStartTime can now come from a previous foreground session, so when ManualAppStartup is started from telemetry during early startup states

What flow would this be? Push notifications? I'm not sure what this problem is.