fix: use robust rolldown shim from PR openclaw#63

Replaces the simpler .pnpm/node_modules/.bin PATH addition with a
proper shell shim that locates rolldown in the pnpm store and creates
a wrapper script. This handles the case where rolldown was removed
from upstream direct dependencies (v2026.2.21+) but remains as a
transitive dep via rolldown-plugin-dts.

Cherry-picked approach from openclaw#63.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: zsoerenm

nix/scripts/gateway-build.sh

@@ -72,9 +72,18 @@ fi
 
 log_step "patchShebangs node_modules/.bin" bash -e -c ". \"$STDENV_SETUP\"; patchShebangs node_modules/.bin"
 
-# Ensure rolldown is found from workspace bins in offline/sandbox builds.
-if [ -d "node_modules/.pnpm/node_modules/.bin" ]; then
-  export PATH="$PWD/node_modules/.pnpm/node_modules/.bin:$PATH"
+# rolldown was removed from upstream direct dependencies (v2026.2.21+) but
+# remains in the pnpm store as a transitive dep (via rolldown-plugin-dts).
+# Upstream's bundle-a2ui.sh falls back to `pnpm dlx` which needs network.
+# Put rolldown on PATH so the script finds it directly.
+if ! command -v rolldown >/dev/null 2>&1; then
+  _rolldown_pkg="$(find node_modules/.pnpm -maxdepth 4 -path '*/rolldown@*/node_modules/rolldown' -print -quit 2>/dev/null || true)"
+  if [ -n "$_rolldown_pkg" ] && [ -f "$_rolldown_pkg/bin/cli.mjs" ]; then
+    _rolldown_shim="$(mktemp -d)"
+    printf '#!/bin/sh\nexec node "%s/bin/cli.mjs" "$@"\n' "$_rolldown_pkg" > "$_rolldown_shim/rolldown"
+    chmod +x "$_rolldown_shim/rolldown"
+    export PATH="$_rolldown_shim:$PATH"
+  fi
 fi
 
 # Break down `pnpm build` (upstream package.json) so we can profile it.