pub async fn run_flush(engine: &Arc<MeruEngine>) -> Result<()>Expand description
Run one flush job: takes the oldest immutable memtable and writes it to L0.
Serialized by engine.flush_mutex so that two concurrently-spawned
auto-flush tasks don’t both observe the same oldest_immutable(),
double-flush it to two L0 Parquet files with identical data, and
double-commit competing Iceberg snapshots (Bug G regression).