fix(middleware): Prevent todo completion reminder IMMessage leak (#2907)

* fix(middleware): Prevent todo completion reminder IMMessage leak (#2892)

* make format

* fix(middleware): Clear stale todo reminder counts (#2892)

* add size guard for _completion_reminder_counts and add a integration test

frontend/src/core/messages/utils.ts

@@ -26,6 +26,13 @@ export type MessageGroup =
   | AssistantClarificationGroup
   | AssistantSubagentGroup;
 
+const HIDDEN_CONTROL_MESSAGE_NAMES = new Set([
+  "summary",
+  "loop_warning",
+  "todo_reminder",
+  "todo_completion_reminder",
+]);
+
 export function getMessageGroups(messages: Message[]): MessageGroup[] {
   if (messages.length === 0) {
     return [];
@@ -53,10 +60,6 @@ export function getMessageGroups(messages: Message[]): MessageGroup[] {
       continue;
     }
 
-    if (message.name === "todo_reminder") {
-      continue;
-    }
-
     if (message.type === "human") {
       groups.push({ id: message.id, type: "human", messages: [message] });
       continue;
@@ -368,8 +371,8 @@ export function findToolCallResult(toolCallId: string, messages: Message[]) {
 export function isHiddenFromUIMessage(message: Message) {
   return (
     message.additional_kwargs?.hide_from_ui === true ||
-    message.name === "summary" ||
-    message.name === "loop_warning"
+    (typeof message.name === "string" &&
+      HIDDEN_CONTROL_MESSAGE_NAMES.has(message.name))
   );
 }
 

frontend/tests/unit/core/messages/utils.test.ts

@@ -63,3 +63,37 @@ test("aggregates token usage messages once per assistant turn", () => {
     ),
   ).toEqual([null, null, ["ai-1", "ai-2"], null, ["ai-3"]]);
 });
+
+test("hides internal todo reminder messages from message groups", () => {
+  const messages = [
+    {
+      id: "human-1",
+      type: "human",
+      content: "Audit the middleware",
+    },
+    {
+      id: "todo-reminder-1",
+      type: "human",
+      name: "todo_completion_reminder",
+      content: "<system_reminder>finish todos</system_reminder>",
+    },
+    {
+      id: "todo-reminder-2",
+      type: "human",
+      name: "todo_reminder",
+      content: "<system_reminder>remember todos</system_reminder>",
+    },
+    {
+      id: "ai-1",
+      type: "ai",
+      content: "Done",
+    },
+  ] as Message[];
+
+  const groups = getMessageGroups(messages);
+
+  expect(groups.map((group) => group.type)).toEqual(["human", "assistant"]);
+  expect(
+    groups.flatMap((group) => group.messages).map((message) => message.id),
+  ).toEqual(["human-1", "ai-1"]);
+});