[fnachabe]

Description
Fixes a cloud synchronization issue where SEMOSS could upload a database engine’s local H2 audit file while H2 was modifying or compacting it.
External databases can return false from holdsFileLocks() because their primary database is remote, even though they still maintain a local audit_log_database.mv.db. Uploading this live file could cause the Azure/Netty chunked uploader to enter a zero-progress CPU loop and stall other cloud-storage requests.

Changes Made
• Close all DATABASE engines before synchronizing their engine folders.
• Preserve the existing holdsFileLocks() behavior for other engine types.
• Reopen database engines after successful synchronization.
• Reopen database engines when synchronization fails.
• Ensure the engine synchronization lock is always released.
• Add unit tests covering:
o External databases without primary file locks.
o Non-database engines without file locks.
o Engine recovery and lock release after transfer failure.
• Update central cloud storage documentation to describe local audit-file handling.

How To Test
From the SEMOSS repository root, run:
mvn -Dtest=prerna.cluster.util.clients.CentralCloudStorageUnitTests test
Verify that the test output ends with:
Failures: 0, Errors: 0
BUILD SUCCESS
For an integration test in a clustered environment:

1. Perform an insert or update against an external database.
2. Confirm the database engine is closed before cloud synchronization.
3. Confirm the engine is reopened after synchronization.
4. Verify the application can continue reading from and writing to the database.
5. Capture two JVM thread dumps approximately 10 seconds apart.
6. Confirm no Reactor thread is continuously consuming a full CPU core in ChunkedNioFile or ChunkedWriteHandler.
7. Confirm the Azure upload completes and other cloud-storage operations remain responsive.

[snyk-io]

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[fnachabe]

Superseded by #3172, which removed the per-engine AuditDatabase and stopped pushing external database engines after writes. The mutable local H2 file that motivated this PR is no longer present in the synchronized engine folder, so closing every database during pushEngine is unnecessary and could disrupt active database operations.