fix(call-omo-agent): validate missing subagent type

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/tools/call-omo-agent/tools.test.ts

@@ -136,6 +136,19 @@ describe("createCallOmoAgent", () => {
   })
 
   describe("dynamic custom agent resolution", () => {
+    test("should reject missing subagent_type without throwing", async () => {
+      const mockCtx = createMockCtx(DEFAULT_AGENTS)
+      const toolDef = createCallOmoAgent(mockCtx, mockBackgroundManager, [])
+      const executeFunc = toolDef.execute as Function
+
+      const result = await executeFunc(
+        { description: "Test", prompt: "Fix bug", run_in_background: true },
+        toolCtx
+      )
+
+      expect(result).toContain("subagent_type is required")
+    })
+
     test("should accept a custom agent returned by client.app.agents()", async () => {
       const agents = [...DEFAULT_AGENTS, { name: "bug-fixer", mode: "subagent" }]
       const mockCtx = createMockCtx(agents)

src/tools/call-omo-agent/tools.ts

@@ -140,6 +140,10 @@ export function createCallOmoAgent(
         `[call_omo_agent] Starting with agent: ${args.subagent_type}, background: ${args.run_in_background}`,
       );
 
+      if (typeof args.subagent_type !== "string" || args.subagent_type.trim() === "") {
+        return "Error: subagent_type is required."
+      }
+
       const callableAgents = await resolveCallableAgents(ctx.client);
 
       // Strip ZWSP and case-insensitive agent validation - allows "Explore", "EXPLORE", "explore" etc.