Type Alias ReduceResult<S, Mapping>

Per-entry narrowed output type for TimeSeries.reduce(mapping). For an AggregateMap with literal reducer names, each field narrows to the specific value kind the reducer produces:

series.reduce({ cpu: 'avg', host: 'unique' });
//    ^ { cpu: number | undefined;
//        host: ReadonlyArray<ScalarValue> | undefined }
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The branches are enumerated inline (rather than delegated to AggregateKindForColumn + NormalizedValueForKind) because the inlined form is the only shape TypeScript accepts in the same compilation unit as the arrayAggregate / arrayExplode overloads — more-delegated variants trip TS2394 on those overloads' compatibility with their implementation signature. The narrow logic is intentionally duplicated here; keep it in sync with AggregateKindForColumn in types.ts if the set of numeric / array-producing reducers changes.

Branches:

• Numeric-output reducers ('sum', 'avg', 'count', 'median', 'stdev', 'difference', any p${number}) → number | undefined.
• Array-output reducers ('unique', any top${number}) → ReadonlyArray<T> | undefined, where T is the source column's element type — ReadonlyArray<string> for a kind: 'string' column, ReadonlyArray<number> for kind: 'number', etc. Array-kind source columns fall back to the wide ReadonlyArray<ScalarValue> | undefined.
• Source-preserving reducers ('first', 'last', 'keep') → the source column's value type (number, string, or boolean — undefined included). Array-kind source columns fall back to ColumnValue | undefined because tracking element kind is out of scope for the schema.
• Custom reducer functions and AggregateOutputSpec entries fall back to ColumnValue | undefined — their output kind is set at runtime and the type system can't see through it.