Static providers (used by smart router) reuse the same Endpoint objects across epochs. The closePurgedUnusedPairingsConnections function was closing these shared connections during epoch transitions, causing "grpc: the client connection is closing" errors for in-flight requests.

This fix skips connection purging for StaticProvider sessions since their connections are intentionally shared and should persist for the lifetime of the process.

Description

Closes: #XXXX

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