Overview

Retryable updates on time-series collections on mongos are dispatched through an internal transaction (AnalysisType::kInternalTransaction). The shard computes query stats execution metrics, but the inner router layer in WriteBatchResponseProcessor::generateClientResponseForBatchWriteCommand only echoes those metrics back to the parent router when the command is forwarded from a router. For the internal-transaction re-route that condition is false, so the metrics are dropped and the router records the query stats entry with zeroed keysExamined, docsExamined, nMatched, and nModified.

Split out from SERVER-121266, which remains open for the retry de-duplication issue (execCount increments on retry).