large_txn_basic.js and prepare_txn_oplog_application_basic.js run prepareTransaction but are not tagged with featureFlagPreparedTransactionsPreciseCheckpoints. In runs where the flag is off (the nightly disagg_storage task on atlas-amazon2023-arm64 / atlas-ubuntu2204-arm64), prepareTransaction is rejected with NotImplemented "Disaggregated Storage does not support cross-shard transactions" and the tests fail.