diff --git a/src/agents/tools/message-tool.test.ts b/src/agents/tools/message-tool.test.ts
index 182693ed0cd..9c541a769a3 100644
--- a/src/agents/tools/message-tool.test.ts
+++ b/src/agents/tools/message-tool.test.ts
@@ -1114,6 +1114,13 @@ describe("message tool reasoning tag sanitization", () => {
       target: "telegram:123",
       channel: "telegram",
     },
+    {
+      field: "message",
+      input: "Reasoning:\n_internal plan_\n_more internal notes_",
+      expected: "",
+      target: "telegram:123",
+      channel: "telegram",
+    },
   ])(
     "sanitizes reasoning tags in $field before sending",
     async ({ channel, target, field, input, expected }) => {