fix(selfhost): opt in stdio MCP via environment

apps/host-selfhost/.env.example

@@ -30,3 +30,9 @@
 # Allow sandboxed code to reach loopback/private network addresses. Off by
 # default — adversarial generated code should not reach your internal network.
 # EXECUTOR_ALLOW_LOCAL_NETWORK=false
+
+# --- Local stdio MCP (trusted deployments only) -------------------------------
+# Stdio MCP is disabled unless this is explicitly set to the exact string
+# "true". Enabling it lets users configure MCP servers whose commands execute
+# on this host.
+# EXECUTOR_ALLOW_STDIO_MCP=true

apps/host-selfhost/executor.config.ts

@@ -19,10 +19,10 @@ import { resolveSecretKey } from "./src/config";
 // Single source of truth for the self-hosted app's plugin list.
 //
 // Self-host runs the same protocol/provider plugins as cloud, minus the
-// multi-tenant-only secret backends (WorkOS Vault). `dangerouslyAllowStdioMCP`
-// is false: a server reachable by multiple users must not let one user spawn
-// arbitrary stdio MCP processes on the host. The encrypted DB secret provider
-// (slice 4) is added here as the first writable secret provider.
+// multi-tenant-only secret backends (WorkOS Vault). Stdio MCP remains opt-in:
+// a server reachable by multiple users must not let one user spawn arbitrary
+// stdio MCP processes on the host. The encrypted DB secret provider (slice 4)
+// is added here as the first writable secret provider.
 // ---------------------------------------------------------------------------
 
 interface SelfHostPluginDeps {
@@ -39,7 +39,9 @@ export default defineExecutorConfig({
         presets: [...googleCatalog, ...microsoftCatalog],
         specFormats: [googleDiscoveryAdapter, microsoftGraphAdapter],
       }),
-      mcpHttpPlugin({ dangerouslyAllowStdioMCP: false }),
+      mcpHttpPlugin({
+        dangerouslyAllowStdioMCP: process.env.EXECUTOR_ALLOW_STDIO_MCP === "true",
+      }),
       graphqlHttpPlugin(),
       toolkitsPlugin({ activeToolkitSlug }),
       // First writable secret provider -> the default for `secrets.set`.

apps/host-selfhost/src/executor-config.test.ts

@@ -0,0 +1,59 @@
+import { afterEach, beforeEach, expect, test } from "@effect/vitest";
+
+import executorConfig from "../executor.config";
+
+const ENV_NAME = "EXECUTOR_ALLOW_STDIO_MCP";
+const SECRET_ENV_NAME = "EXECUTOR_SECRET_KEY";
+const originalValue = process.env[ENV_NAME];
+const originalSecret = process.env[SECRET_ENV_NAME];
+
+beforeEach(() => {
+  process.env[SECRET_ENV_NAME] = originalSecret ?? "executor-config-test-secret";
+});
+
+afterEach(() => {
+  if (originalValue === undefined) {
+    delete process.env[ENV_NAME];
+  } else {
+    process.env[ENV_NAME] = originalValue;
+  }
+  if (originalSecret === undefined) {
+    delete process.env[SECRET_ENV_NAME];
+  } else {
+    process.env[SECRET_ENV_NAME] = originalSecret;
+  }
+});
+
+const allowStdio = (): boolean => {
+  const mcp = executorConfig.plugins().find((plugin) => plugin.id === "mcp");
+  expect(mcp).toBeDefined();
+  const clientConfig = mcp?.clientConfig;
+  if (
+    clientConfig &&
+    typeof clientConfig === "object" &&
+    "allowStdio" in clientConfig &&
+    typeof clientConfig.allowStdio === "boolean"
+  ) {
+    return clientConfig.allowStdio;
+  }
+  expect.fail("MCP plugin did not expose its stdio setting");
+  return false;
+};
+
+test("stdio MCP stays disabled when the opt-in is absent", () => {
+  delete process.env[ENV_NAME];
+  expect(allowStdio()).toBe(false);
+});
+
+test("stdio MCP stays disabled unless the opt-in is exactly true", () => {
+  process.env[ENV_NAME] = "false";
+  expect(allowStdio()).toBe(false);
+
+  process.env[ENV_NAME] = "TRUE";
+  expect(allowStdio()).toBe(false);
+});
+
+test("stdio MCP is enabled when the opt-in is exactly true", () => {
+  process.env[ENV_NAME] = "true";
+  expect(allowStdio()).toBe(true);
+});