diff --git a/src/agents/bash-tools.exec.ts b/src/agents/bash-tools.exec.ts
index 7896f9b6d1f..cf5f901c65c 100644
--- a/src/agents/bash-tools.exec.ts
+++ b/src/agents/bash-tools.exec.ts
@@ -828,16 +828,15 @@ export function createExecTool(
     label: "exec",
     description:
       "Execute shell commands with background continuation. Use yieldMs/background to continue later via process tool. Use pty=true for TTY-required commands (terminal UIs, coding agents).",
-    parameters: {
-      ...execSchema,
-      properties: {
-        ...execSchema.properties,
-        host: {
-          ...execSchema.properties.host,
+    parameters: Type.Object({
+      ...execSchema.properties,
+      host: Type.Optional(
+        Type.String({
+          description: "Exec host (sandbox|gateway|node).",
           default: defaults?.host ?? "sandbox",
-        },
-      },
-    },
+        }),
+      ),
+    }),
     execute: async (_toolCallId, args, signal, onUpdate) => {
       const params = args as {
         command: string;