feat(install): handle updates — stop old daemon, back up, install new version

- detect installed version via --version; skip when already up to date
- stop the running daemon and keep agent-arka.previous rollback copy on upgrade/downgrade

agent-arka/install.sh

@@ -157,6 +157,19 @@ ensure_path() {
     warn "Added ${bindir} to PATH in ${rc} (open a new shell, or: source ${rc})"
 }
 
+# Normalize a CalVer "YYYY.M.D" into a single sortable integer (YYYYMMDD pads).
+ver_cmp_key() {
+    printf '%s' "$1" | awk -F. '{ printf "%04d%02d%02d", $1, $2, $3 }' 2>/dev/null || printf '%s' 0
+}
+
+# Installed version, or empty when there is no binary/detectable version.
+installed_version() {
+    local bin="$1" out
+    [[ -x "$bin" ]] || return 1
+    out=$("$bin" --version 2>/dev/null | head -n 1) || return 1
+    printf '%s\n' "$out" | grep -oE '[0-9]{4}\.[0-9]+(\.[0-9]+)?' | tail -n 1
+}
+
 main() {
     printf '%s\n' "${C_BOLD}Agent Arka${C_RESET} — web dashboard installer"
     command -v curl >/dev/null 2>&1 || die "curl is required"
@@ -183,6 +196,31 @@ main() {
         info "Latest: ${version}"
     fi
 
+    # Update handling: detect an existing install and skip / stop / back it up.
+    local existing
+    existing=$(installed_version "${bindir}/agent-arka" 2>/dev/null || true)
+    if [[ -n "$existing" ]]; then
+        local ek tk
+        ek=$(ver_cmp_key "$existing")
+        tk=$(ver_cmp_key "$version")
+        if [[ "$ek" == "$tk" ]]; then
+            info "Already up to date: agent-arka ${existing} (target ${version})"
+            ensure_path "$bindir"
+            return 0
+        fi
+        if [[ "$ek" -gt "$tk" ]]; then
+            warn "Downgrading ${existing} -> ${version}"
+        else
+            info "Upgrading ${existing} -> ${version}"
+        fi
+        # Bring the running daemon down before replacing the binary.
+        if AGENT_ARKA_HOME="${HOME_DIR}" LIBREFANG_HOME="${HOME_DIR}" "${bindir}/agent-arka" stop >/dev/null 2>&1; then
+            ok "Stopped running agent-arka ${existing}"
+        fi
+        # Keep a rollback copy of the current binary.
+        cp -f "${bindir}/agent-arka" "${bindir}/agent-arka.previous" 2>/dev/null || true
+    fi
+
     local tag="${TAG_PREFIX}${version}"
     local asset="agent-arka-${version}-${PLATFORM}.tar.gz"
     local url="${PUBLIC_DL}/${tag}/${asset}"