diff --git a/src/web/auto-reply/util.test.ts b/src/web/auto-reply/util.test.ts
new file mode 100644
index 00000000000..18e627ce88d
--- /dev/null
+++ b/src/web/auto-reply/util.test.ts
@@ -0,0 +1,51 @@
+import { describe, expect, it } from "vitest";
+import { elide, isLikelyWhatsAppCryptoError } from "./util.js";
+
+describe("web auto-reply util", () => {
+  describe("elide", () => {
+    it("returns undefined for undefined input", () => {
+      expect(elide(undefined)).toBe(undefined);
+    });
+
+    it("returns input when under limit", () => {
+      expect(elide("hi", 10)).toBe("hi");
+    });
+
+    it("returns input when exactly at limit", () => {
+      expect(elide("12345", 5)).toBe("12345");
+    });
+
+    it("truncates and annotates when over limit", () => {
+      expect(elide("abcdef", 3)).toBe("abc… (truncated 3 chars)");
+    });
+  });
+
+  describe("isLikelyWhatsAppCryptoError", () => {
+    it("returns false for non-matching reasons", () => {
+      expect(isLikelyWhatsAppCryptoError(new Error("boom"))).toBe(false);
+      expect(isLikelyWhatsAppCryptoError("boom")).toBe(false);
+      expect(isLikelyWhatsAppCryptoError({ message: "bad mac" })).toBe(false);
+    });
+
+    it("matches known Baileys crypto auth errors (string)", () => {
+      expect(
+        isLikelyWhatsAppCryptoError(
+          "baileys: unsupported state or unable to authenticate data (noise-handler)",
+        ),
+      ).toBe(true);
+      expect(isLikelyWhatsAppCryptoError("bad mac in aesDecryptGCM (baileys)")).toBe(true);
+    });
+
+    it("matches known Baileys crypto auth errors (Error)", () => {
+      const err = new Error("bad mac");
+      err.stack = "at something\nat @whiskeysockets/baileys/noise-handler\n";
+      expect(isLikelyWhatsAppCryptoError(err)).toBe(true);
+    });
+
+    it("does not throw on circular objects", () => {
+      const circular: Record<string, unknown> = {};
+      circular.self = circular;
+      expect(isLikelyWhatsAppCryptoError(circular)).toBe(false);
+    });
+  });
+});