Add Support for RangeIndex Diskbased Replication

[vazois]

Summary

Adds support for shipping RangeIndex (BfTree) files during disk-based cluster replication, so replicas can fully recreate range index state after checkpoint recovery.

Work Items

• Validate flush cleanup safety
• Replica-side flush.bftree cleanup on resync
• Add CheckpointFileType entries (STORE_RANGEINDEX_FLUSH, STORE_RANGEINDEX_SNAPSHOT)
• Implement RangeIndex data source (RangeIndexFileDataSource)
• Implement RangeIndex transmit source (RangeIndexFileTransmitSource)
• Implement RangeIndexSnapshotReader
• Implement RangeIndex data sink (RangeIndexFileDataSink)
• Integrate into ReceiveCheckpointHandler
• Integrate into ReplicaSyncSession
• Implement replication tests

Changes

Primary Side (Sender)

• File enumeration: RangeIndexManager.EnumerateFilesForReplication() yields all flush and snapshot .bftree files for a given checkpoint
• Data source: RangeIndexFileDataSource — FileStream-based chunked reader with GetMetadata() for binary serialization of keyHash + address
• Transmit source: RangeIndexFileTransmitSource — sends metadata header (startAddress=-1) then streams file content in 128KB chunks
• Snapshot reader: RangeIndexSnapshotReader — ISnapshotReader that enumerates RI files and yields transmit sources
• Session integration: ReplicaSyncSession.SendCheckpointAsync adds RangeIndexSnapshotReader to the transmission driver when EnableRangeIndexPreview is set

Replica Side (Receiver)

• Data sink: RangeIndexFileDataSink with FromMetadata() factory — zero-copy deserialization from metadata span, derives target path via RangeIndexManager helpers, writes chunks via FileStream
• Handler integration: ReceiveCheckpointHandler.ProcessSnapshotData handles RI metadata headers and file segments

Shared Infrastructure

• CheckpointFileType enum: Added STORE_RANGEINDEX_FLUSH=7, STORE_RANGEINDEX_SNAPSHOT=8
• Visibility: Made LogFlushPath, CheckpointSnapshotPath, rangeIndexManager public for cross-assembly access

Wire Protocol

Each RI file is transmitted as:

1. Header (startAddress=-1): binary metadata — keyHash (32B ASCII) + address (8B LE for flush)
2. Content chunks (startAddress=offset): raw file data in 128KB chunks
3. End marker (empty data): signals completion

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Adds disk-based replication support for RangeIndex (BfTree) files so replicas can restore RangeIndex state after checkpoint recovery.

Changes:

• Add replication plumbing for RangeIndex flush/snapshot .bftree files (enumeration, reader, transmit source, receiver sink, handler integration).
• Update server gating: allow RangeIndex preview in cluster mode except for diskless replication.
• Add a new cluster test project and plumb enableRangeIndexPreview through test helpers/context.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
test/standalone/Garnet.test/TestUtils.cs	Adds enableRangeIndexPreview parameter forwarding for test server options.
test/cluster/Garnet.test.cluster/ClusterTestContext.cs	Adds enableRangeIndexPreview option to cluster test instance creation paths.
test/cluster/Garnet.test.cluster.replication.rangeindex/Garnet.test.cluster.replication.rangeindex.csproj	Introduces a new test project for RangeIndex replication scenarios.
test/cluster/Garnet.test.cluster.replication.rangeindex/ClusterRangeIndexReplicationTests.cs	Adds end-to-end cluster replication tests for RangeIndex behavior.
libs/server/StoreWrapper.cs	Exposes rangeIndexManager for cross-assembly replication usage.
libs/server/Resp/RangeIndex/RangeIndexManager.cs	Adds RI file enumeration helpers and replication file listing API.
libs/host/GarnetServer.cs	Updates validation to disallow RI preview only in diskless replication mode.
libs/cluster/Server/Replication/ReplicaOps/DiskbasedReplication/ReceiveCheckpointHandler.cs	Adds handling to create RI sinks from metadata headers.
libs/cluster/Server/Replication/ReplicaOps/DiskbasedReplication/RangeIndexFileDataSink.cs	Implements replica-side sink that writes received RI file bytes to disk.
libs/cluster/Server/Replication/PrimaryOps/DiskbasedReplication/ReplicaSyncSession.cs	Adds RangeIndexSnapshotReader to checkpoint transmission when RI preview enabled.
libs/cluster/Server/Replication/PrimaryOps/DiskbasedReplication/RangeIndexSnapshotReader.cs	Enumerates RI files for a checkpoint and yields transmit sources.
libs/cluster/Server/Replication/PrimaryOps/DiskbasedReplication/RangeIndexFileTransmitSource.cs	Sends RI metadata header + chunked file bytes + end marker over snapshot protocol.
libs/cluster/Server/Replication/PrimaryOps/DiskbasedReplication/RangeIndexFileDataSource.cs	Implements FileStream-backed chunk reader plus metadata generation for RI files.
libs/cluster/Server/Replication/CheckpointFileType.cs	Adds two new CheckpointFileType values for RI flush/snapshot files.
Garnet.slnx	Adds the new RangeIndex replication test project to the solution.