aggregateSeries

Aggregates a Series into a one-slot chunk with the kernel agg ("sum", "count", "mean", "min", "max", "first", "last"), in the result dtype section 6.4 assigns.

Dispatch: sum, mean, min and max compute their per-chunk partials through runSegments above the row threshold (independent chunks only - sub-chunk segments would change the float association for identical chunking - combined on the caller in chunk order, so the bits equal the serial walk's at every thread count). count is metadata over nullCount, first/last are endpoint reads and the BOOLEAN sum is word-wise popcnt; none of them gain from dispatch and stay serial.