Callers that arrive while a refresh of one linked identity is in flight in
this process join it and receive its success or failure, instead of queuing
on the row lock and presenting the same refresh token again behind a failed
holder. The entry lives as long as the attempt, so a later request retries.
The store lock stays the cross-process guard; the residual risk (one
presentation per process per burst) is written into the service contract.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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