"$RUST_HOST；" is one variable name to macOS /bin/sh (bash 3.2): it
swallows the first byte of the full-width punctuation, so with set -u a
plain \`sh install.sh app\` aborted at [3/4] with "RUST_HOST\*: unbound
variable". Four such lines in install.sh, one in the server setup.
Brace them, add make lint-sh (sh -n for every shipped script plus a
check for this pattern) so it stays fixed.
王性驊