coalesce_runs
coalesce_runs(
plan: ChunkPlan ,
working: DataFrame ,
)-> ‘ChunkPlan’
Merge each output’s consecutive members cut from one patch’s runs.
A patch cut by with_runs plans stretch by stretch (its rows share one _patch_row), so a hole can end an output; the stretches landing in one output are read from their patch once, as one member spanning them.