The watchdog only log.Fatal'd with a message, so a hung test told us
that it timed out but not where it was stuck -- useless for diagnosing
an intermittent deadlock under the race detector. Dump all goroutine
stacks to stderr first (the harness surfaces this process's stderr on
failure), turning a bare timeout into an actionable stack trace.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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