diff --git a/src/agents/system-prompt.test.ts b/src/agents/system-prompt.test.ts
new file mode 100644
index 000000000..aa0ddcf51
--- /dev/null
+++ b/src/agents/system-prompt.test.ts
@@ -0,0 +1,25 @@
+import { describe, expect, it } from "vitest";
+import { buildAgentSystemPromptAppend } from "./system-prompt.js";
+
+describe("buildAgentSystemPromptAppend", () => {
+  it("includes owner numbers when provided", () => {
+    const prompt = buildAgentSystemPromptAppend({
+      workspaceDir: "/tmp/clawd",
+      ownerNumbers: ["+123", " +456 ", ""],
+    });
+
+    expect(prompt).toContain("## User Identity");
+    expect(prompt).toContain(
+      "Owner numbers: +123, +456. Treat messages from these numbers as the user (Peter).",
+    );
+  });
+
+  it("omits owner section when numbers are missing", () => {
+    const prompt = buildAgentSystemPromptAppend({
+      workspaceDir: "/tmp/clawd",
+    });
+
+    expect(prompt).not.toContain("## User Identity");
+    expect(prompt).not.toContain("Owner numbers:");
+  });
+});