NIFI-16351 - Prevent Flow Registry synchronization failures during startup validation

[pvillard31]

Summary

NIFI-16351 - Prevent Flow Registry synchronization failures during startup validation

Flow Registry synchronization can run while a restored Flow Registry Client is still VALIDATING. During startup, client validation cannot begin until flow initialization completes, but version-controlled process groups submit synchronization tasks while the flow is still being restored.

When restoration takes longer than the existing 10-second validation wait, synchronization records a misleading flow-retrieval failure. Recovery then depends on the delayed periodic synchronization task.

This change:

• Treats VALIDATING as a transient condition without replacing the current synchronization status.
• Handles INVALID as a durable validation-specific failure.
• Applies validation-state handling before both registry access paths.
• Includes the underlying exception message in snapshot-retrieval failures.
• Submits one Flow Registry synchronization pass after initial validation and after releasing the FlowController write lock.
• Reuses the same RegistryFlowSynchronizationTask used for periodic synchronization, preserving per-client grouping and interval tracking.
• Leaves the existing 300-second periodic initial delay and configured synchronization interval unchanged.

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  • JDK 21
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