When running inside a sandbox (e.g., bubblewrap) that blocks access
to the tmux socket, the tmux query hangs and times out, returning
undefined. Previously this was treated as "extended-keys is off",
showing a false warning. Now we skip the warning when the tmux server
can't be reached.
Use pipeline() instead of finished(readable.pipe(writable)) so stream
errors from abort signals are caught as promise rejections. Increase
download timeout from 10s to 120s for multi-MB archives.
closes#2066