basalt-26.3.2-rc-20260908: kv/kvserver: TestStoreRangeMergeSplitRace_MergeWins failed

kv/kvserver.TestStoreRangeMergeSplitRace_MergeWins [failed](https://mesolite.cluster.engflow.com/invocations/default/4e6b3e4b-4f3a-4ae0-ac38-acabe7fa7d66?testReportRun=2&testReportShard=2&testReportAttempt=1#targets-Ly9wa2cva3Yva3ZzZXJ2ZXI6a3ZzZXJ2ZXJfdGVzdA==) on basalt-26.3.2-rc-20260908 @ [807558e5e81666af257c811e925e4cae570abc28](https://github.com/cockroachdb/cockroach/commits/807558e5e81666af257c811e925e4cae570abc28):

```
=== RUN TestStoreRangeMergeSplitRace_MergeWins
test_log_scope.go:172: test logs captured to: outputs.zip/logTestStoreRangeMergeSplitRace_MergeWins1300959415
test_log_scope.go:82: use -show-logs to present logs inline
test_server_shim.go:146: using test tenant configuration from testserver factory defaults
test_server_shim.go:639: DRPC is enabled (via testserver factory defaults)
client_merge_test.go:1655: merge failed: checking RHS manifest before merge: descriptor generation mismatch: expected 2, found 3
panic.go:694: -- test log scope end --
test logs left over in: outputs.zip/logTestStoreRangeMergeSplitRace_MergeWins1300959415
--- FAIL: TestStoreRangeMergeSplitRace_MergeWins (5.14s)
```

Parameters:
- attempt=1
- race=true
- run=2
- shard=2
Help

See also: [How To Investigate a Go Test Failure \(internal\)](https://cockroachlabs.atlassian.net/l/c/HgfXfJgM)

Same failure on other branches

- #174777 kv/kvserver: TestStoreRangeMergeSplitRace_MergeWins failed [C-test-failure O-robot T-kv branch-master release-blocker]

/cc @cockroachlabs/kv-triage

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