Function choose_trace_reconcile_decision 

pub(super) fn choose_trace_reconcile_decision(
    column_name: &str,
    observed_types: &[ColumnDataType],
    existing_type: Option<ColumnDataType>,
) -> Result<Option<TraceReconcileDecision>>

Picks the reconciliation action for one trace column.

Existing table schema is authoritative unless the only incompatible case is widening an existing Int64 column to Float64 for incoming Int64/Float64 data.