[ci] XAGCPU7000 "device offline" during -t:Install in on-device package tests #11830

Summary

The emulator/device intermittently goes offline during the -t:Install step of the on-device package tests, causing error XAGCPU7000: Mono.AndroidTools.AdbException: device offline. Because the install step currently runs with continueOnError: true, the failure is swallowed, the pipeline still attempts dotnet test (which then fails with INSTRUMENTATION_FAILED since the app was never installed), and the lane is only marked red at the end by the fail if any issues occurred gate.

This is infrastructure flakiness, not a product/test regression.

Evidence

Observed on PR #11804, build 1488505 — job Package Tests > macOS > Tests > APKs 1:

Install step (build Mono.Android.NET_Tests-Debug, -t:Install):

Xamarin.Android.Common.Debugging.targets(107,2): error XAGCPU7000: Mono.AndroidTools.AdbException: device offline
   at Mono.AndroidTools.Util.AggregateAsyncResult.CheckError(CancellationToken token)
   at Mono.AndroidTools.Adb.AdbClient.EndConnectTransport(IAsyncResult asyncResult)
   ...
Build FAILED.

Downstream run step (run Mono.Android.NET_Tests-Debug):

INSTRUMENTATION_FAILED: Mono.Android.NET_Tests/xamarin.android.runtimetests.TestInstrumentation

The Release and NoAab flavors in the same job installed and ran fine — only the Debug install caught the offline moment.

Impact

• Flaky red PR checks unrelated to the change under test.
• Wasted CI time: the pipeline runs dotnet test against a device where the app was never installed.

Proposed / related fix

Stop swallowing install failures: remove continueOnError: true from the -t:Install step in build-tools/automation/yaml-templates/apk-instrumentation.yaml so a failed install fails the lane immediately instead of running tests that cannot pass. (PR to follow.)

This does not fix the root cause (emulator/ADB going offline) but makes the failure fail fast and unambiguous. The underlying emulator/ADB stability issue is what this issue tracks.

Notes

XAGCPU7000 is emitted from Xamarin.Android.Common.Debugging.targets. Investigate whether a transient ADB reconnect/retry around device connect during Install would absorb these blips.