Point package managers at China mirrors on cn installs

npm, PyPI and uv, Go, rustup and crates.io, RubyGems and Bundler,
and Maven reach their registries slowly or not at all from China.
On a cn install, link the profile's environment, cargo and gem
drop-ins into place. A regular file the admin wrote is never
replaced; the install fails instead.

test/shell.d/region-test.sh

@@ -0,0 +1,47 @@
+#!/bin/bash
+
+set -euo pipefail
+
+source "$(cd -- "$(dirname -- "${BASH_SOURCE[0]}")" && pwd)/base-test.sh"
+
+test_tmp=$(mktemp -d)
+trap 'rm -rf "$test_tmp"' EXIT
+
+region_setup="$test_tmp/region.sh"
+root="$test_tmp/root"
+sed -e "s|/etc/|$root/etc/|g" -e "s| /\.cargo/| $root/.cargo/|g" "$ROOT/install/config/region.sh" >"$region_setup"
+export OMARCHY_PATH="$ROOT"
+mkdir -p "$root/etc/omarchy"
+
+bash -e "$region_setup"
+[[ -z $(find "$root" -type l) ]] || fail "no marker links nothing"
+pass "no marker installs Global"
+
+echo cn >"$root/etc/omarchy/region"
+bash -e "$region_setup"
+for link in "environment.conf etc/environment.d/90-omarchy-china.conf" "cargo.toml .cargo/config.toml" "gemrc etc/gemrc"; do
+  read -r source target <<<"$link"
+  [[ $(readlink "$root/$target") == "$ROOT/default/regions/cn/$source" ]] || fail "China links /$target to the shipped $source"
+done
+bash -e "$region_setup"
+pass "the cn marker links the developer mirror drop-ins, again without error"
+
+rm "$root/etc/gemrc"
+echo ":sources: []" >"$root/etc/gemrc"
+if output=$(bash -e "$region_setup" 2>&1); then
+  fail "China refuses to replace an admin's /etc/gemrc" "$output"
+fi
+[[ $output == "Refusing to replace $root/etc/gemrc, which Omarchy did not create" && $(<"$root/etc/gemrc") == ":sources: []" ]] ||
+  fail "China names the file it refuses to replace and leaves it" "$output"
+rm "$root/etc/gemrc"
+pass "region setup never replaces mirror config Omarchy did not create"
+
+echo mars >"$root/etc/omarchy/region"
+if output=$(bash -e "$region_setup" 2>&1); then
+  fail "an unknown region fails" "$output"
+fi
+[[ $output == "Unknown region: mars" ]] || fail "region setup names the unknown region" "$output"
+pass "region setup rejects an unknown region"
+
+grep -qx 'run_logged "$OMARCHY_INSTALL/config/region.sh"' "$ROOT/install/config/all.sh" || fail "the install runs region setup"
+pass "the install runs region setup"