fix(gateway-tests): flush gateway config state before server start

What:
- persist unsynced gateway test session config before each fresh startGatewayServer call
- reset config runtime state and clear the session store cache before starting a new gateway server in tests

Why:
- current Linux CI failures span auth, talk, reload, chat, and config behavior at once
- the common seam is fresh test servers starting against stale cached config/session state

Tests:
- sh -n nix/scripts/gateway-postpatch.sh
- targeted transform dry-run against pinned OpenClaw source rev 89535f9313579e791b3ed325b2cb64fecdd978f7

nix/scripts/gateway-postpatch.sh

@@ -63,6 +63,23 @@ PY
   fi
 fi
 
+if [ -f src/gateway/test-helpers.server.ts ]; then
+  if ! grep -q "Flush config/session caches before each fresh gateway start." src/gateway/test-helpers.server.ts; then
+    python3 - <<'PY'
+from pathlib import Path
+
+path = Path("src/gateway/test-helpers.server.ts")
+text = path.read_text()
+
+old = """export async function startGatewayServer(port: number, opts?: GatewayServerOptions) {\n  const mod = await getServerModule();\n"""
+new = """export async function startGatewayServer(port: number, opts?: GatewayServerOptions) {\n  if (hasUnsyncedGatewayTestSessionConfig()) {\n    await persistTestSessionConfig();\n  }\n  // Flush config/session caches before each fresh gateway start.\n  resetConfigRuntimeState();\n  clearSessionStoreCacheForTest();\n  const mod = await getServerModule();\n"""
+if old not in text:
+    raise SystemExit("expected startGatewayServer helper block not found")
+path.write_text(text.replace(old, new, 1))
+PY
+  fi
+fi
+
 if [ -f src/plugins/provider-runtime.ts ]; then
   if ! grep -q "shouldSkipProviderRuntimeForTest" src/plugins/provider-runtime.ts; then
     python3 - <<'PY'