diff --git a/tests/unit/chat-log-array-tail-items-default.test.ts b/tests/unit/chat-log-array-tail-items-default.test.ts
new file mode 100644
index 0000000000..fa2bc4fb1f
--- /dev/null
+++ b/tests/unit/chat-log-array-tail-items-default.test.ts
@@ -0,0 +1,27 @@
+/**
+ * Regression test for the CHAT_LOG_ARRAY_TAIL_ITEMS default bump 24 -> 128.
+ *
+ * Real agentic CLIs with many MCP servers routinely declare 40-50+ tools in
+ * a single request — a live OpenClaw session logged 47. The old tail-24
+ * default silently dropped the array's earlier entries behind an
+ * `_omniroute_truncated_array` marker, including (in one traced case) the
+ * tool actually being called, making its declared shape unrecoverable from
+ * the call log even though the call itself succeeded.
+ *
+ * Pins the literal default so a future edit can't silently regress it back
+ * toward the old, too-small value.
+ */
+import { test } from "node:test";
+import assert from "node:assert/strict";
+import { getChatLogArrayTailItems } from "@/lib/logEnv";
+
+test("getChatLogArrayTailItems defaults to 128 (not the old 24) when unset", () => {
+  const saved = process.env.CHAT_LOG_ARRAY_TAIL_ITEMS;
+  delete process.env.CHAT_LOG_ARRAY_TAIL_ITEMS;
+  try {
+    assert.equal(getChatLogArrayTailItems(), 128);
+  } finally {
+    if (saved === undefined) delete process.env.CHAT_LOG_ARRAY_TAIL_ITEMS;
+    else process.env.CHAT_LOG_ARRAY_TAIL_ITEMS = saved;
+  }
+});