[beekld]

Summary

Since #489, the data system has silently ignored a synchronizer result with State: Off. The result's error was dropped, the status didn't change, and the data system kept waiting on that synchronizer. A synchronizer isn't supposed to report Off, but State is a public field, and custom synchronizers can set it.

This PR treats an Off result as an unexpected failure. The data system reports Interrupted with the result's error and parks the synchronizer.

It also changes how the data system handles a synchronizer that closes its result channel on its own. That used to count as a fallback, which with a single synchronizer restarted it at once with no delay. A synchronizer that kept ending its results could then restart in a tight loop. The data system now treats this as an unexpected failure too, and parks the synchronizer.

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Note

Overview
Fixes FDv2 synchronizer handling for two invalid behaviors that could leave the client stuck or spinning.

State: Off from a synchronizer is no longer ignored. The data system now surfaces Interrupted with the result’s error, marks the outcome as an unexpected failure, and parks the synchronizer (or restarts from the first synchronizer if the SDK key changed mid-run).

When a synchronizer closes its own result channel, the loop no longer treats that as a normal fallback (which could restart a lone synchronizer immediately in a tight loop). It reports Interrupted with a fixed unknown error, then parks or restarts the same way as other unexpected failures.

Tests assert both paths: status/error reporting and that the primary synchronizer does not run again while parked.

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