The IDE backend is uploaded by streaming it into `gzip -dc > file` on the
host. When that command exits early (no gzip, a folder it cannot write, a
full disk), it stops reading: once the channel window (about 2 MB) is
used up, the next write waited for window space forever, so Remote
Development stayed on "Installing the IDE backend on the host…" at a few
percent and never showed the host's error. Each write, and closing the
input, now races the command's exit; an early exit ends the upload with
the command's status and stderr.
Refs #1330
l0ng-ai