Large copy buffer deadlock

[idle-meerkat]

FYI dvtm reads from editor only after it exits.
if the copied buffer is larger than 65k (pipe default limit on linux) dvtm-editor waits on write to pipe.
in my fork I made the read in dvtm async:
idle-meerkat/my-dvtm@2fb27e0
later going to refactor this and make all similar operations async.