diff --git a/extensions/telegram/src/message-cache.test.ts b/extensions/telegram/src/message-cache.test.ts
index 77920877e2e3..58dd96ee3ada 100644
--- a/extensions/telegram/src/message-cache.test.ts
+++ b/extensions/telegram/src/message-cache.test.ts
@@ -1,4 +1,4 @@
-import { readFile, rm } from "node:fs/promises";
+import { readFile, rm, writeFile } from "node:fs/promises";
 import type { Message } from "@grammyjs/types";
 import { describe, expect, it, vi } from "vitest";
 import {
@@ -8,6 +8,28 @@ import {
   resolveTelegramMessageCachePath,
 } from "./message-cache.js";
 
+type PersistedCacheEntry = {
+  key: string;
+  node: {
+    sourceMessage: Message;
+  };
+};
+
+function persistedCacheEntry(messageId: number, text: string): PersistedCacheEntry {
+  return {
+    key: `default:7:${messageId}`,
+    node: {
+      sourceMessage: {
+        chat: { id: 7, type: "group", title: "Ops" },
+        message_id: messageId,
+        date: 1736380000 + messageId,
+        text,
+        from: { id: messageId, is_bot: false, first_name: `User ${messageId}` },
+      } as Message,
+    },
+  };
+}
+
 describe("telegram message cache", () => {
   it("hydrates reply chains from persisted cached messages", async () => {
     const storePath = `/tmp/openclaw-telegram-message-cache-${process.pid}-${Date.now()}.json`;
@@ -253,6 +275,54 @@ describe("telegram message cache", () => {
     }
   });
 
+  it("loads mixed legacy array caches and rewrites them as line-delimited entries", async () => {
+    const storePath = `/tmp/openclaw-telegram-message-cache-legacy-${process.pid}-${Date.now()}.json`;
+    const persistedPath = resolveTelegramMessageCachePath(storePath);
+    await rm(persistedPath, { force: true });
+    try {
+      const legacyEntries = [
+        persistedCacheEntry(35033, "ocdbg-5818 one"),
+        persistedCacheEntry(35034, "ocdbg-5818 two"),
+        persistedCacheEntry(35035, "ocdbg-5818 three"),
+      ];
+      const appendedEntries = [
+        persistedCacheEntry(35036, "ocdbg-5818 four"),
+        persistedCacheEntry(35037, "ocdbg-5818 five"),
+      ];
+      await writeFile(
+        persistedPath,
+        `${JSON.stringify(legacyEntries)}${appendedEntries.map((entry) => JSON.stringify(entry)).join("\n")}\n`,
+      );
+
+      const cache = createTelegramMessageCache({ persistedPath });
+
+      expect(
+        cache
+          .around({
+            accountId: "default",
+            chatId: 7,
+            messageId: "35035",
+            before: 2,
+            after: 2,
+          })
+          .map((entry) => entry.messageId),
+      ).toEqual(["35033", "35034", "35035", "35036", "35037"]);
+
+      const canonical = await readFile(persistedPath, "utf-8");
+      expect(canonical.startsWith("[")).toBe(false);
+      const lines = canonical.trim().split("\n");
+      expect(lines).toHaveLength(5);
+      expect(
+        lines.map((line) => {
+          const entry = JSON.parse(line) as PersistedCacheEntry;
+          return entry.node.sourceMessage.message_id;
+        }),
+      ).toEqual([35033, 35034, 35035, 35036, 35037]);
+    } finally {
+      await rm(persistedPath, { force: true });
+    }
+  });
+
   it("returns recent chat messages before the current message", () => {
     const cache = createTelegramMessageCache();
     for (const id of [41, 42, 43, 44]) {