[rit3sh-x]

Summary

Fixes a data race between IAVL's exporter and Node.clone when the node cache is enabled.

A persisted node can be shared by an ImmutableTree and a concurrently-mutating MutableTree. Node.clone previously cleared the persisted node's leftNode and rightNode pointers after resolving them from the tree.

This mutates a node that may simultaneously be read by an exporter, causing a race under -race.

Changes

• Remove the two leftNode = nil / rightNode = nil writes from Node.clone.
• Add a comment documenting why persisted nodes must not be mutated during cloning.
• Add TestExporter_ConcurrentSet, which reproduces the Cosmos SDK state-sync pattern:
  • Save version N.
  • Create an immutable tree for version N.
  • Start an exporter for version N.
  • Write version N+1 using the same mutable tree/cache.
  • Import the exported version into a fresh tree.
  • Verify the imported hash matches version N.

Validation

• go test -short -race ./...: passed
• go test ./...: passed
• GOARCH=386 go test ./...: passed
• TestExporter_ConcurrentSet: passed across 50 runs with -race

[greptile-apps]

This PR does not match any of the 1 configured review trigger rule.

[rit3sh-x]

@cloudhead could you review it?