diff --git a/src/cron/service.jobs.test.ts b/src/cron/service.jobs.test.ts
index e80e957d62e..787e8f6ef81 100644
--- a/src/cron/service.jobs.test.ts
+++ b/src/cron/service.jobs.test.ts
@@ -152,6 +152,79 @@ describe("applyJobPatch", () => {
     ).not.toThrow();
     expect(job.delivery).toEqual({ mode: "webhook", to: "https://example.invalid/trim" });
   });
+
+  it("rejects Telegram delivery with invalid target (slash delimiter)", () => {
+    const job = createIsolatedAgentTurnJob("job-telegram-invalid", {
+      mode: "announce",
+      channel: "telegram",
+      to: "-10012345/6789",
+    });
+
+    expect(() => applyJobPatch(job, { enabled: true })).toThrow(
+      'Invalid Telegram delivery target "-10012345/6789". Use colon (:) as delimiter, not slash or other characters. Valid formats: -1001234567890, -1001234567890:123, -1001234567890:topic:123',
+    );
+  });
+
+  it("rejects Telegram delivery with other invalid characters", () => {
+    const job = createIsolatedAgentTurnJob("job-telegram-invalid-space", {
+      mode: "announce",
+      channel: "telegram",
+      to: "-10012345 6789",
+    });
+
+    expect(() => applyJobPatch(job, { enabled: true })).toThrow(
+      'Invalid Telegram delivery target "-10012345 6789". Use colon (:) as delimiter, not slash or other characters. Valid formats: -1001234567890, -1001234567890:123, -1001234567890:topic:123',
+    );
+  });
+
+  it("accepts Telegram delivery with valid target (plain chat id)", () => {
+    const job = createIsolatedAgentTurnJob("job-telegram-valid", {
+      mode: "announce",
+      channel: "telegram",
+      to: "-1001234567890",
+    });
+
+    expect(() => applyJobPatch(job, { enabled: true })).not.toThrow();
+  });
+
+  it("accepts Telegram delivery with valid target (colon delimiter)", () => {
+    const job = createIsolatedAgentTurnJob("job-telegram-valid-colon", {
+      mode: "announce",
+      channel: "telegram",
+      to: "-1001234567890:123",
+    });
+
+    expect(() => applyJobPatch(job, { enabled: true })).not.toThrow();
+  });
+
+  it("accepts Telegram delivery with valid target (topic marker)", () => {
+    const job = createIsolatedAgentTurnJob("job-telegram-valid-topic", {
+      mode: "announce",
+      channel: "telegram",
+      to: "-1001234567890:topic:456",
+    });
+
+    expect(() => applyJobPatch(job, { enabled: true })).not.toThrow();
+  });
+
+  it("accepts Telegram delivery without target", () => {
+    const job = createIsolatedAgentTurnJob("job-telegram-no-target", {
+      mode: "announce",
+      channel: "telegram",
+    });
+
+    expect(() => applyJobPatch(job, { enabled: true })).not.toThrow();
+  });
+
+  it("accepts Telegram delivery with @username", () => {
+    const job = createIsolatedAgentTurnJob("job-telegram-username", {
+      mode: "announce",
+      channel: "telegram",
+      to: "@mybot",
+    });
+
+    expect(() => applyJobPatch(job, { enabled: true })).not.toThrow();
+  });
 });
 
 function createMockState(now: number): CronServiceState {
diff --git a/src/cron/service/jobs.ts b/src/cron/service/jobs.ts
index 19b8d26e91b..dc403585574 100644
--- a/src/cron/service/jobs.ts
+++ b/src/cron/service/jobs.ts
@@ -83,6 +83,19 @@ export function assertSupportedJobSpec(job: Pick<CronJob, "sessionTarget" | "pay
   }
 }
 
+const INVALID_TELEGRAM_TARGET_CHARS = ["/", "\\", " ", ",", ";"];
+
+function validateTelegramDeliveryTarget(to: string | undefined): string | undefined {
+  if (!to) {
+    return undefined;
+  }
+  const hasInvalidChar = INVALID_TELEGRAM_TARGET_CHARS.some((char) => to.includes(char));
+  if (hasInvalidChar) {
+    return `Invalid Telegram delivery target "${to}". Use colon (:) as delimiter, not slash or other characters. Valid formats: -1001234567890, -1001234567890:123, -1001234567890:topic:123`;
+  }
+  return undefined;
+}
+
 function assertDeliverySupport(job: Pick<CronJob, "sessionTarget" | "delivery">) {
   if (!job.delivery) {
     return;
@@ -98,6 +111,12 @@ function assertDeliverySupport(job: Pick<CronJob, "sessionTarget" | "delivery">)
   if (job.sessionTarget !== "isolated") {
     throw new Error('cron channel delivery config is only supported for sessionTarget="isolated"');
   }
+  if (job.delivery.channel === "telegram") {
+    const telegramError = validateTelegramDeliveryTarget(job.delivery.to);
+    if (telegramError) {
+      throw new Error(telegramError);
+    }
+  }
 }
 
 export function findJobOrThrow(state: CronServiceState, id: string) {