5.6.18

• Added getOption("gmultitasking.strategy") for gextract (default "auto"). When the workload is large and many-track, auto routes to a track-parallel mode (each parallel::mclapply worker handles a track subset across all tiles) instead of the legacy tile-parallel mode (each fork-kid handles a tile range across all tracks). On the realistic 3,110 motif tracks × 2.19M tiled_peaks workload measured 57.6 min vs ~3.4 h projected for tile-parallel — a 3.5× per-track speedup. Override per-call via options(gmultitasking.strategy = "tracks" | "tiles" | "auto"). The heuristic stays on "tiles" for streaming iterators (numeric / NULL / 2D rect / track-name), single-track or fewer than 8 tracks, file/intervals.set.out output, or 2D band — so nothing else regresses (validated by a 36-cell matrix bench across iterator types × track counts × cache states).