fix: Improve fallback behavior when using custom data system configuration

[devin-ai-integration]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions

Related issues

Ports the same fix from the Go SDK: launchdarkly/go-server-sdk#348

Describe the solution you've provided

Removes the interrupted_at_runtime and cannot_initialize conditions from _recovery_condition in the FDv2 data system. Recovery (jumping back to the first/preferred synchronizer) now only triggers when the current non-primary synchronizer has been VALID for more than 5 minutes.

The removed conditions could cause premature recovery attempts that interfere with data system configurations using more than two synchronizers. The _fallback_condition (which moves forward through synchronizers) is unchanged and still uses both interrupted_at_runtime and cannot_initialize.

Human review checklist

• Verify that only the recovery condition should be changed, and that the fallback condition (_fallback_condition at line 632) is intentionally left as-is
• Confirm alignment with the Go SDK fix
• Assess whether existing test coverage for recovery behavior is sufficient

Additional context

Link to Devin run | Requested by @keelerm84

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Note

Medium Risk
Changes FDv2 synchronizer switching logic, which can affect availability and how multi-synchronizer configurations behave during outages. Risk is moderate due to potential impact on failover/recovery timing, though the change is small and localized.

Overview
FDv2’s recovery behavior when running on a non-primary synchronizer is tightened so it only switches back to the preferred (index 0) synchronizer after the current one has been VALID for more than 5 minutes.

This removes recovery triggers based on being INTERRUPTED for 1 minute or stuck INITIALIZING for 10 seconds, reducing premature “jump back” behavior in configurations with multiple synchronizers; the forward fallback logic in _fallback_condition remains unchanged.

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[devin-ai-integration]

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