merchantPost now retries once after clearing the cached token and
re-authenticating when the upstream signals an invalid session:
HTML login page, HTTP 401, or business msgs containing login-expiry
keywords. Previously a stale token left stock queries returning
empty until manual intervention.
Generated with [Devin](https://devin.ai)
Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>
chiyiandDevin
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