basalt-26.3.2-rc-20260908: testutils/testcluster: TestClusterStart failed

testutils/testcluster.TestClusterStart [failed](https://mesolite.cluster.engflow.com/invocations/default/6cda6f11-f948-43b1-8648-858357aa7fb3?testReportRun=2&testReportShard=1&testReportAttempt=1#targets-Ly9wa2cvdGVzdHV0aWxzL3Rlc3RjbHVzdGVyOnRlc3RjbHVzdGVyX3Rlc3Q=) on basalt-26.3.2-rc-20260908 @ [807558e5e81666af257c811e925e4cae570abc28](https://github.com/cockroachdb/cockroach/commits/807558e5e81666af257c811e925e4cae570abc28):

```
=== RUN TestClusterStart
test_log_scope.go:172: test logs captured to: outputs.zip/logTestClusterStart3826593858
test_log_scope.go:82: use -show-logs to present logs inline
test_server_shim.go:168: automatically injected a shared process virtual cluster under test; see comment at top of test_server_shim.go for details.
```

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

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

/cc @cockroachlabs/test-eng

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Start with the linked test report for testutils/testcluster.TestClusterStart and inspect outputs.zip/logTestClusterStart3826593858, using -show-logs if needed. Read the comment at the top of test_server_shim.go to understand the injected virtual cluster, then reproduce the failure with race=true. Done means TestClusterStart passes reliably for the reported configuration.

Written by the indexing model from the issue text.