[iOS, macOS] fix screen time watchdog crash and fire pixel when there is data on launch

[brindy]

Task/Issue URL: https://app.asana.com/1/137249556945/project/414235014887631/task/1216744184761157?focus=true
Tech Design URL:
CC:

Description

Improves Screen Time data cleanup on iOS/macOS 26 by using the dedicated system API while retaining the existing fallback. Adds daily and count telemetry when Screen Time records remain at launch, without reporting record counts or URLs.

Testing Steps

1. On iOS 26, disable the Screen Time cleaning feature flag.

2. Launch the app and visit a website.

3. Background and relaunch the app → screen-time_records-present daily and count pixels are emitted.

4. Enable the Screen Time cleaning feature flag.

5. Background the app to trigger cleanup.

6. Relaunch the app → no Screen Time records pixel is emitted.

7. Build the iOS Browser scheme → build succeeds.

8. Smoke test macOS app

Impact

High: A cleanup regression could leave browsing activity visible through Screen Time, affecting user privacy.

What could go wrong?

Screen Time records could remain after cleanup → mitigated by retaining the existing WebKit cleanup as a fallback.

The telemetry could report false positives → mitigated by checking both the dedicated Screen Time API and WebKit data stores.

Quality Considerations

• The dedicated Screen Time work runs outside the main actor to reduce watchdog risk.
• The WebKit cross-check remains main-actor isolated as required by the SDK and includes cancellation checks.
• Telemetry reports only whether records exist. It does not include URLs, record counts, or other browsing information.
• The change applies only to iOS/macOS 26 and later.

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Internal references:

Definition of Done | Engineering Expectations | Tech Design Template

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Note

High Risk
Changes the Screen Time cleanup and detection path for privacy-sensitive browsing history; a regression could leave records visible or affect launch-time behavior, though WebKit fallback remains.

Overview
On iOS/macOS 26+, ScreenTimeDataCleaner now tries the Screen Time STWebHistory path first for both detecting and removing browsing history, and only falls back to scanning/removing WKWebsiteDataTypeScreenTime across WebKit data stores when that path is unavailable or fails. Public cleanup/detection APIs are no longer fully @MainActor; WebKit work stays on the main actor with cancellation checks, and the cleaner is marked Sendable.

Launch registers an iOS 26+ startup task that calls hasScreenTimeData() and fires the screen-time_records-present pixel (daily + count) when records still exist—without URLs or counts. A matching pixel definition is added in screen_time.json5.

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[samsymons]

LGTM, worked as expected - thanks!