diff --git a/src/cron/isolated-agent.test.ts b/src/cron/isolated-agent.test.ts
index ff71c7fe4..c9677c7f7 100644
--- a/src/cron/isolated-agent.test.ts
+++ b/src/cron/isolated-agent.test.ts
@@ -20,7 +20,10 @@ vi.mock("../agents/model-catalog.js", () => ({
 
 import { loadModelCatalog } from "../agents/model-catalog.js";
 import { runEmbeddedPiAgent } from "../agents/pi-embedded.js";
-import { runCronIsolatedAgentTurn } from "./isolated-agent.js";
+import {
+  parseTelegramTarget,
+  runCronIsolatedAgentTurn,
+} from "./isolated-agent.js";
 
 async function withTempHome<T>(fn: (home: string) => Promise<T>): Promise<T> {
   const base = await fs.mkdtemp(path.join(os.tmpdir(), "clawdbot-cron-"));
@@ -670,3 +673,47 @@ describe("runCronIsolatedAgentTurn", () => {
     });
   });
 });
+
+describe("parseTelegramTarget", () => {
+  it("parses plain chatId", () => {
+    expect(parseTelegramTarget("-1001234567890")).toEqual({
+      chatId: "-1001234567890",
+      topicId: undefined,
+    });
+  });
+
+  it("parses @username", () => {
+    expect(parseTelegramTarget("@mychannel")).toEqual({
+      chatId: "@mychannel",
+      topicId: undefined,
+    });
+  });
+
+  it("parses chatId:topicId format", () => {
+    expect(parseTelegramTarget("-1001234567890:123")).toEqual({
+      chatId: "-1001234567890",
+      topicId: 123,
+    });
+  });
+
+  it("parses chatId:topic:topicId format", () => {
+    expect(parseTelegramTarget("-1001234567890:topic:456")).toEqual({
+      chatId: "-1001234567890",
+      topicId: 456,
+    });
+  });
+
+  it("trims whitespace", () => {
+    expect(parseTelegramTarget("  -1001234567890:99  ")).toEqual({
+      chatId: "-1001234567890",
+      topicId: 99,
+    });
+  });
+
+  it("does not treat non-numeric suffix as topicId", () => {
+    expect(parseTelegramTarget("-1001234567890:abc")).toEqual({
+      chatId: "-1001234567890:abc",
+      topicId: undefined,
+    });
+  });
+});
diff --git a/src/cron/isolated-agent.ts b/src/cron/isolated-agent.ts
index a7d756a1a..0cc056c5a 100644
--- a/src/cron/isolated-agent.ts
+++ b/src/cron/isolated-agent.ts
@@ -50,6 +50,36 @@ import { resolveTelegramToken } from "../telegram/token.js";
 import { normalizeE164 } from "../utils.js";
 import type { CronJob } from "./types.js";
 
+/**
+ * Parse a Telegram delivery target into chatId and optional topicId.
+ * Supports formats:
+ * - `chatId` (plain chat ID or @username)
+ * - `chatId:topicId` (chat ID with topic/thread ID)
+ * - `chatId:topic:topicId` (alternative format with explicit "topic" marker)
+ */
+export function parseTelegramTarget(to: string): {
+  chatId: string;
+  topicId: number | undefined;
+} {
+  const trimmed = to.trim();
+
+  // Try format: chatId:topic:topicId
+  const topicMatch = /^(.+?):topic:(\d+)$/.exec(trimmed);
+  if (topicMatch) {
+    return { chatId: topicMatch[1], topicId: parseInt(topicMatch[2], 10) };
+  }
+
+  // Try format: chatId:topicId (where topicId is numeric)
+  // Be careful not to match @username or other non-numeric suffixes
+  const colonMatch = /^(.+):(\d+)$/.exec(trimmed);
+  if (colonMatch) {
+    return { chatId: colonMatch[1], topicId: parseInt(colonMatch[2], 10) };
+  }
+
+  // Plain chatId, no topic
+  return { chatId: trimmed, topicId: undefined };
+}
+
 export type RunCronAgentTurnResult = {
   status: "ok" | "error" | "skipped";
   summary?: string;
@@ -487,7 +517,7 @@ export async function runCronIsolatedAgentTurn(params: {
           summary: "Delivery skipped (no Telegram chatId).",
         };
       }
-      const chatId = resolvedDelivery.to;
+      const { chatId, topicId } = parseTelegramTarget(resolvedDelivery.to);
       const textLimit = resolveTextChunkLimit(params.cfg, "telegram");
       try {
         for (const payload of payloads) {
@@ -501,6 +531,7 @@ export async function runCronIsolatedAgentTurn(params: {
               await params.deps.sendMessageTelegram(chatId, chunk, {
                 verbose: false,
                 token: telegramToken || undefined,
+                messageThreadId: topicId,
               });
             }
           } else {
@@ -512,6 +543,7 @@ export async function runCronIsolatedAgentTurn(params: {
                 verbose: false,
                 mediaUrl: url,
                 token: telegramToken || undefined,
+                messageThreadId: topicId,
               });
             }
           }