ffmpeg and ffprobe are console-subsystem binaries and Node defaults
windowsHide to false, so every spawn opened a visible console window on
Windows. A render shells out dozens of times across parallel workers,
which flashed a burst of windows across the user's desktop.
Applied at every production spawn site rather than only the two named in
the report, since they all share the cause: runFfmpeg, both gpuEncoder
probes, ffprobe, streamingEncoder, audioExtractor and the distributed
version check. windowsHide is a no-op on macOS and Linux.
The dev-only parity and regression harnesses are left alone; they never
run on a user's desktop.
Closes#3379
Miguel Ángel
315a7b758c