Initialize FileCache for warm index on node boot-up/restart

[skumawat2025]

Description

This PR:

• Implements local file scanning to warm up fileCache during node startup, reducing remote store downloads
• Logic to cleans up index and shard paths during warm index deletion. Reference PR.
• Fixes flaky tests in WarmIndexSegmentReplicationIT

Related Issues

Resolves #17526, #18157

Check List

• Functionality includes testing.
• API changes companion pull request created, if applicable.
• Public documentation issue/PR created, if applicable.

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[github-actions]

❌ Gradle check result for 8c2bb1b: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for ef7f263: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for 7d8da5c: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[reta]

@skumawat2025 to answer your question, why the Detect Breaking Changes check fails:

You are modifying public method of the @PublicApi class by adding new argument - this will breaking each and every caller of this method if any.

How to fix it: bring the existing method back, mark it @Deprecated(forRemoval = true) and delegate to the new method:

    @Deprecated(forRemoval = true) 
    public static List<Path> collectFileCacheDataPath(NodePath fileCacheNodePath) throws IOException {
        return collectFileCacheDataPath(fileCacheNodePath, Settings.EMPTY);
    }

[skumawat2025]

@skumawat2025 to answer your question, why the Detect Breaking Changes check fails:

You are modifying public method of the @PublicApi class by adding new argument - this will breaking each and every caller of this method if any.

How to fix it: bring the existing method back, mark it @Deprecated(forRemoval = true) and delegate to the new method:

    @Deprecated(forRemoval = true) 
    public static List<Path> collectFileCacheDataPath(NodePath fileCacheNodePath) throws IOException {
        return collectFileCacheDataPath(fileCacheNodePath, Settings.EMPTY);
    }

Thanks @reta this fixed the issue.

[github-actions]

✅ Gradle check result for b92b514: SUCCESS

[github-actions]

❕ Gradle check result for f6edc15: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[skumawat2025]

Have run the WarmIndexSegmentReplicationIT 600+ times successfully and still running. Will keep monitoring for any flakiness.

BUILD SUCCESSFUL in 1m 31s
66 actionable tasks: 1 executed, 65 up-to-date
[2025-06-17 19:11:14] : ===================================================================
[2025-06-17 19:11:14] : counter=605
[2025-06-17 19:11:14] : ===================================================================
> Task :buildSrc:reaper:compileJava UP-TO-DATE