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.ts

@@ -123,6 +123,29 @@ export function isSafeToRetrySendError(err: unknown): boolean {
   return false;
 }
 
+function hasTelegramErrorCode(err: unknown, matches: (code: number) => boolean): boolean {
+  for (const candidate of collectTelegramErrorCandidates(err)) {
+    if (!candidate || typeof candidate !== "object" || !("error_code" in candidate)) {
+      continue;
+    }
+    const code = (candidate as { error_code: unknown }).error_code;
+    if (typeof code === "number" && matches(code)) {
+      return true;
+    }
+  }
+  return false;
+}
+
+/** Returns true for HTTP 5xx server errors (error may have been processed). */
+export function isTelegramServerError(err: unknown): boolean {
+  return hasTelegramErrorCode(err, (code) => code >= 500);
+}
+
+/** Returns true for HTTP 4xx client errors (Telegram explicitly rejected, not applied). */
+export function isTelegramClientRejection(err: unknown): boolean {
+  return hasTelegramErrorCode(err, (code) => code >= 400 && code < 500);
+}
+
 export function isRecoverableTelegramNetworkError(
   err: unknown,
   options: { context?: TelegramNetworkErrorContext; allowMessageMatch?: boolean } = {},