The `commitTransaction` command is defined in the IDL as strict, so older versions may not be able to understand the newly added `endOfTransactionScopes` field that the txn coordinator can send since SERVER-137904. In a mixed-version cluster (running 9.1/master for the transaction coordinator and 9.0 for a participant shard), it is possible that the receiving shard cannot parse the `commitTransaction` command request with the extra metadata sent by the coordinator. This situation is now auto-detected, and the coordinator now retries sending the command with the metadata stripped.

To avoid unnecessary retries on the hot commit path, a shard's eligibility is cached in a per-process cache. The cache records if a recipient shard is unable to parse the commit message. The cache entries are keyed by recipient shard id. The cache entries have a TTL of 5 minutes. This bounds the number of commit retries to 1 per ineligible shard per every 5 minutes.