How this run's files were split across those groups — the descriptive record RunResult reports. Assigned once per run alongside groupCount and shared by reference, so a group can read the whole split rather than only its own slice.

Empty until a split is computed, which is why groupCount stays the authority the runner branches on: page reuse is decided during daemon setup, before any grouping exists. Watch never splits at all, so it leaves this empty and the result names its one group from the files that rerun ran.