fix(telegram): suppress message_thread_id for private chat sends (#17242)

Private chats (positive numeric chat IDs) never support forum topics.
Sending message_thread_id to a private chat causes Telegram to reject
the request with '400: Bad Request: message thread not found', silently
dropping the message.

Guard all three send functions (sendMessageTelegram, sendStickerTelegram,
sendPollTelegram) to omit thread-related parameters when the target is a
private chat.

Root cause: the auto-reply pipeline can set messageThreadId from a
previous forum-group context, then reuse it when sending a DM.

Tests: add private-chat suppression assertions; update existing thread-
retry tests to use group chat IDs so the retry path is still exercised.

src/telegram/send.test.ts

@@ -850,8 +850,55 @@ describe("sendMessageTelegram", () => {
     });
   });
 
+  it("suppresses message_thread_id for private chat sends (#17242)", async () => {
+    // Private chats have positive numeric IDs; they never support forum topics.
+    const chatId = "123456789";
+    const sendMessage = vi.fn().mockResolvedValue({
+      message_id: 56,
+      chat: { id: chatId },
+    });
+    const api = { sendMessage } as unknown as {
+      sendMessage: typeof sendMessage;
+    };
+
+    await sendMessageTelegram(chatId, "hello private", {
+      token: "tok",
+      api,
+      messageThreadId: 271,
+    });
+
+    // message_thread_id must NOT appear in private chats -- Telegram rejects it
+    // with "400: Bad Request: message thread not found".
+    expect(sendMessage).toHaveBeenCalledWith(chatId, "hello private", {
+      parse_mode: "HTML",
+    });
+  });
+
+  it("keeps message_thread_id for group chat sends (#17242)", async () => {
+    // Group/supergroup chats have negative IDs.
+    const chatId = "-1001234567890";
+    const sendMessage = vi.fn().mockResolvedValue({
+      message_id: 57,
+      chat: { id: chatId },
+    });
+    const api = { sendMessage } as unknown as {
+      sendMessage: typeof sendMessage;
+    };
+
+    await sendMessageTelegram(chatId, "hello group", {
+      token: "tok",
+      api,
+      messageThreadId: 271,
+    });
+
+    expect(sendMessage).toHaveBeenCalledWith(chatId, "hello group", {
+      parse_mode: "HTML",
+      message_thread_id: 271,
+    });
+  });
+
   it("retries without message_thread_id when Telegram reports missing thread", async () => {
-    const chatId = "123";
+    const chatId = "-100123";
     const threadErr = new Error("400: Bad Request: message thread not found");
     const sendMessage = vi
       .fn()
@@ -963,7 +1010,7 @@ describe("sendMessageTelegram", () => {
   });
 
   it("retries media sends without message_thread_id when thread is missing", async () => {
-    const chatId = "123";
+    const chatId = "-100123";
     const threadErr = new Error("400: Bad Request: message thread not found");
     const sendPhoto = vi
       .fn()
@@ -1084,7 +1131,7 @@ describe("sendStickerTelegram", () => {
   });
 
   it("retries sticker sends without message_thread_id when thread is missing", async () => {
-    const chatId = "123";
+    const chatId = "-100123";
     const threadErr = new Error("400: Bad Request: message thread not found");
     const sendSticker = vi
       .fn()
@@ -1337,7 +1384,7 @@ describe("sendPollTelegram", () => {
     };
 
     const res = await sendPollTelegram(
-      "123",
+      "-100123",
       { question: "Q", options: ["A", "B"] },
       { token: "t", api: api as unknown as Bot["api"], messageThreadId: 99 },
     );

src/telegram/send.ts

@@ -196,6 +196,17 @@ function isTelegramMessageNotModifiedError(err: unknown): boolean {
   return MESSAGE_NOT_MODIFIED_RE.test(formatErrorMessage(err));
 }
 
+/**
+ * Telegram private chats have positive numeric IDs.
+ * Groups and supergroups have negative IDs (typically -100… for supergroups).
+ * Private chats never support forum topics, so `message_thread_id` must
+ * not be included in API calls targeting them (#17242).
+ */
+function isTelegramPrivateChat(chatId: string): boolean {
+  const n = Number(chatId);
+  return Number.isFinite(n) && n > 0;
+}
+
 function hasMessageThreadIdParam(params?: Record<string, unknown>): boolean {
   if (!params) {
     return false;
@@ -428,9 +439,10 @@ export async function sendMessageTelegram(
   const mediaUrl = opts.mediaUrl?.trim();
   const replyMarkup = buildInlineKeyboard(opts.buttons);
 
+  const isPrivate = isTelegramPrivateChat(chatId);
   const threadParams = buildTelegramThreadReplyParams({
-    targetMessageThreadId: target.messageThreadId,
+    targetMessageThreadId: isPrivate ? undefined : target.messageThreadId,
-    messageThreadId: opts.messageThreadId,
+    messageThreadId: isPrivate ? undefined : opts.messageThreadId,
     replyToMessageId: opts.replyToMessageId,
     quoteText: opts.quoteText,
   });
@@ -919,9 +931,10 @@ export async function sendStickerTelegram(
   const target = parseTelegramTarget(to);
   const chatId = normalizeChatId(target.chatId);
 
+  const isPrivate = isTelegramPrivateChat(chatId);
   const threadParams = buildTelegramThreadReplyParams({
-    targetMessageThreadId: target.messageThreadId,
+    targetMessageThreadId: isPrivate ? undefined : target.messageThreadId,
-    messageThreadId: opts.messageThreadId,
+    messageThreadId: isPrivate ? undefined : opts.messageThreadId,
     replyToMessageId: opts.replyToMessageId,
   });
   const hasThreadParams = Object.keys(threadParams).length > 0;
@@ -997,9 +1010,10 @@ export async function sendPollTelegram(
   // Normalize the poll input (validates question, options, maxSelections)
   const normalizedPoll = normalizePollInput(poll, { maxOptions: 10 });
 
+  const isPrivate = isTelegramPrivateChat(chatId);
   const threadParams = buildTelegramThreadReplyParams({
-    targetMessageThreadId: target.messageThreadId,
+    targetMessageThreadId: isPrivate ? undefined : target.messageThreadId,
-    messageThreadId: opts.messageThreadId,
+    messageThreadId: isPrivate ? undefined : opts.messageThreadId,
     replyToMessageId: opts.replyToMessageId,
   });