diff --git a/test/hooks.agentId.test.ts b/test/hooks.agentId.test.ts
new file mode 100644
index 000000000..7684a9b08
--- /dev/null
+++ b/test/hooks.agentId.test.ts
@@ -0,0 +1,68 @@
+import { describe, it, expect } from "vitest";
+import { normalizeAgentPayload } from "../src/gateway/hooks.js";
+
+describe("normalizeAgentPayload agentId support", () => {
+  it("should accept agentId as a string", () => {
+    const payload = {
+      message: "test message",
+      channel: "last",
+      agentId: "agent-123",
+    };
+    const result = normalizeAgentPayload(payload);
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.agentId).toBe("agent-123");
+    }
+  });
+
+  it("should trim agentId whitespace", () => {
+    const payload = {
+      message: "test message",
+      channel: "last",
+      agentId: "  agent-456  ",
+    };
+    const result = normalizeAgentPayload(payload);
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.agentId).toBe("agent-456");
+    }
+  });
+
+  it("should handle missing agentId as undefined", () => {
+    const payload = {
+      message: "test message",
+      channel: "last",
+    };
+    const result = normalizeAgentPayload(payload);
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.agentId).toBeUndefined();
+    }
+  });
+
+  it("should ignore empty agentId strings", () => {
+    const payload = {
+      message: "test message",
+      channel: "last",
+      agentId: "  ",
+    };
+    const result = normalizeAgentPayload(payload);
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.agentId).toBeUndefined();
+    }
+  });
+
+  it("should handle non-string agentId as undefined", () => {
+    const payload = {
+      message: "test message",
+      channel: "last",
+      agentId: 123,
+    } as any;
+    const result = normalizeAgentPayload(payload);
+    expect(result.ok).toBe(true);
+    if (result.ok) {
+      expect(result.value.agentId).toBeUndefined();
+    }
+  });
+});