fix(bootstrap): keep the nano build toolchain under /opt/felis

The source build of the nano binary installed Go at /usr/local/go and
replaced whatever version was already there. On a host that also
builds other things, the operator's own toolchain was removed and
swapped for Felis's pinned version without a word.

GOROOT_DIR is now /opt/felis/go, next to the source, the Velocity
install and the JRE Felis already keeps under /opt/felis, and
install_go_toolchain creates the parent before unpacking. A host where
an earlier run put Go at /usr/local/go downloads it once more on the
next re-run and keeps the old tree untouched; removing it is the
operator's call. The harness now requires the toolchain directory to
be under /opt/felis.

deploy/bootstrap.sh

@@ -200,7 +200,9 @@ PANEL_TLS_CERT="${STATE_DIR}/panel-tls.crt"
 PANEL_TLS_KEY="${STATE_DIR}/panel-tls.key"
 SRC_DIR="/opt/felis/src"
 HOST_BIN="/usr/local/bin/felis"
-GOROOT_DIR="/usr/local/go"
+# Felis's own build toolchain, not /usr/local/go: install_go_toolchain replaces whatever
+# version sits here, and an operator's Go at the conventional path is not ours to swap.
+GOROOT_DIR="/opt/felis/go"
 NANO_SERVICE="/etc/systemd/system/felis-nano.service"
 VELOCITY_DIR="/opt/felis/velocity"
 VELOCITY_USER="felis-velocity"
@@ -2321,6 +2323,7 @@ install_go_toolchain() {
   have="$(sha256sum <"${tmp}/${tarball}" | cut -d' ' -f1)"
   [ "$have" = "$want" ] || die "Go ${FELIS_GO_VERSION} (${arch}) checksum mismatch: got ${have}, expected ${want}"
   rm -rf "$GOROOT_DIR"
+  mkdir -p "$(dirname "$GOROOT_DIR")"
   tar -C "$(dirname "$GOROOT_DIR")" -xzf "${tmp}/${tarball}" || die "failed to unpack ${tarball}"
   ok "go toolchain at ${GOROOT_DIR}/bin/go"
 }

deploy/bootstrap_test.sh

@@ -473,8 +473,15 @@ else
 fi
 
 # --- install_go_toolchain checks the tarball before it replaces anything ----------------
-# The tarball is unpacked into /usr/local and run as root, so a download that does not hash
+# The tarball is unpacked and run as root, so a download that does not hash to the pin is
-# to the pin is refused -- and refused before the working toolchain is removed.
+# refused -- and refused before the working toolchain is removed.
+
+# The function replaces whatever version sits at GOROOT_DIR, so that has to be a directory
+# Felis owns, never an operator's /usr/local/go.
+case "$(grep '^GOROOT_DIR=' "$BS")" in
+  'GOROOT_DIR="/opt/felis/'*) echo "PASS the Go toolchain lives under /opt/felis" ;;
+  *) echo "FAIL the Go toolchain must live under /opt/felis, got: $(grep '^GOROOT_DIR=' "$BS")"; fails=$((fails + 1)) ;;
+esac
 
 gblock="$(awk '/^install_go_toolchain\(\) \{/,/^}/' "$BS")"
 [ -n "$gblock" ] || { echo "FAIL: no install_go_toolchain found in $BS"; exit 1; }