fix(telegram): prevent duplicate messages with slow LLM providers (#41932)

Merged via squash.

Prepared head SHA: 2f50c51d5a
Co-authored-by: hougangdev <105773686+hougangdev@users.noreply.github.com>
Co-authored-by: obviyus <22031114+obviyus@users.noreply.github.com>
Reviewed-by: @obviyus

src/telegram/network-errors.test.ts

@@ -1,5 +1,10 @@
 import { describe, expect, it } from "vitest";
-import { isRecoverableTelegramNetworkError, isSafeToRetrySendError } from "./network-errors.js";
+import {
+  isRecoverableTelegramNetworkError,
+  isSafeToRetrySendError,
+  isTelegramClientRejection,
+  isTelegramServerError,
+} from "./network-errors.js";
 
 describe("isRecoverableTelegramNetworkError", () => {
   it("detects recoverable error codes", () => {
@@ -164,3 +169,51 @@ describe("isSafeToRetrySendError", () => {
     expect(isSafeToRetrySendError(wrapped)).toBe(true);
   });
 });
+
+describe("isTelegramServerError", () => {
+  it("returns true for error_code 500", () => {
+    const err = Object.assign(new Error("Internal Server Error"), { error_code: 500 });
+    expect(isTelegramServerError(err)).toBe(true);
+  });
+
+  it("returns true for error_code 502", () => {
+    const err = Object.assign(new Error("Bad Gateway"), { error_code: 502 });
+    expect(isTelegramServerError(err)).toBe(true);
+  });
+
+  it("returns false for error_code 403", () => {
+    const err = Object.assign(new Error("Forbidden"), { error_code: 403 });
+    expect(isTelegramServerError(err)).toBe(false);
+  });
+
+  it("returns false for plain Error", () => {
+    expect(isTelegramServerError(new Error("500: Internal Server Error"))).toBe(false);
+  });
+});
+
+describe("isTelegramClientRejection", () => {
+  it("returns true for error_code 400", () => {
+    const err = Object.assign(new Error("Bad Request"), { error_code: 400 });
+    expect(isTelegramClientRejection(err)).toBe(true);
+  });
+
+  it("returns true for error_code 403", () => {
+    const err = Object.assign(new Error("Forbidden"), { error_code: 403 });
+    expect(isTelegramClientRejection(err)).toBe(true);
+  });
+
+  it("returns false for error_code 502", () => {
+    const err = Object.assign(new Error("Bad Gateway"), { error_code: 502 });
+    expect(isTelegramClientRejection(err)).toBe(false);
+  });
+
+  it("returns false for plain Error", () => {
+    expect(isTelegramClientRejection(new Error("400: Bad Request"))).toBe(false);
+  });
+
+  it("detects error_code in nested cause", () => {
+    const inner = Object.assign(new Error("Forbidden"), { error_code: 403 });
+    const outer = Object.assign(new Error("wrapped"), { cause: inner });
+    expect(isTelegramClientRejection(outer)).toBe(true);
+  });
+});