fix: chunk long html telegram sends

src/telegram/format.test.ts

@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { markdownToTelegramHtml } from "./format.js";
+import { markdownToTelegramHtml, splitTelegramHtmlChunks } from "./format.js";
 
 describe("markdownToTelegramHtml", () => {
   it("handles core markdown-to-telegram conversions", () => {
@@ -112,4 +112,12 @@ describe("markdownToTelegramHtml", () => {
     expect(res).toContain("<tg-spoiler>secret</tg-spoiler>");
     expect(res).toContain("trailing ||");
   });
+
+  it("splits long html text without breaking balanced tags", () => {
+    const chunks = splitTelegramHtmlChunks(`<b>${"A".repeat(5000)}</b>`, 4000);
+    expect(chunks.length).toBeGreaterThan(1);
+    expect(chunks.every((chunk) => chunk.length <= 4000)).toBe(true);
+    expect(chunks[0]).toMatch(/^<b>.*<\/b>$/);
+    expect(chunks[1]).toMatch(/^<b>.*<\/b>$/);
+  });
 });

src/telegram/format.ts

@@ -241,6 +241,158 @@ export function renderTelegramHtmlText(
   return markdownToTelegramHtml(text, { tableMode: options.tableMode });
 }
 
+type TelegramHtmlTag = {
+  name: string;
+  openTag: string;
+  closeTag: string;
+};
+
+const TELEGRAM_SELF_CLOSING_HTML_TAGS = new Set(["br"]);
+
+function buildTelegramHtmlOpenPrefix(tags: TelegramHtmlTag[]): string {
+  return tags.map((tag) => tag.openTag).join("");
+}
+
+function buildTelegramHtmlCloseSuffix(tags: TelegramHtmlTag[]): string {
+  return tags
+    .slice()
+    .toReversed()
+    .map((tag) => tag.closeTag)
+    .join("");
+}
+
+function buildTelegramHtmlCloseSuffixLength(tags: TelegramHtmlTag[]): number {
+  return tags.reduce((total, tag) => total + tag.closeTag.length, 0);
+}
+
+function findTelegramHtmlSafeSplitIndex(text: string, maxLength: number): number {
+  if (text.length <= maxLength) {
+    return text.length;
+  }
+  const normalizedMaxLength = Math.max(1, Math.floor(maxLength));
+  let splitAt = normalizedMaxLength;
+  const lastAmpersand = text.lastIndexOf("&", normalizedMaxLength - 1);
+  const lastSemicolon = text.lastIndexOf(";", normalizedMaxLength - 1);
+  if (lastAmpersand > lastSemicolon) {
+    splitAt = lastAmpersand;
+  }
+  return splitAt > 0 ? splitAt : normalizedMaxLength;
+}
+
+function popTelegramHtmlTag(tags: TelegramHtmlTag[], name: string): void {
+  for (let index = tags.length - 1; index >= 0; index -= 1) {
+    if (tags[index]?.name === name) {
+      tags.splice(index, 1);
+      return;
+    }
+  }
+}
+
+export function splitTelegramHtmlChunks(html: string, limit: number): string[] {
+  if (!html) {
+    return [];
+  }
+  const normalizedLimit = Math.max(1, Math.floor(limit));
+  if (html.length <= normalizedLimit) {
+    return [html];
+  }
+
+  const chunks: string[] = [];
+  const openTags: TelegramHtmlTag[] = [];
+  let current = "";
+  let chunkHasContent = false;
+
+  const resetCurrent = () => {
+    current = buildTelegramHtmlOpenPrefix(openTags);
+    chunkHasContent = false;
+  };
+
+  const flushCurrent = () => {
+    if (!chunkHasContent) {
+      return;
+    }
+    chunks.push(`${current}${buildTelegramHtmlCloseSuffix(openTags)}`);
+    resetCurrent();
+  };
+
+  const appendText = (segment: string) => {
+    let remaining = segment;
+    while (remaining.length > 0) {
+      const available =
+        normalizedLimit - current.length - buildTelegramHtmlCloseSuffixLength(openTags);
+      if (available <= 0) {
+        const prefix = buildTelegramHtmlOpenPrefix(openTags);
+        if (!chunkHasContent && current === prefix) {
+          current += remaining;
+          chunkHasContent = true;
+          remaining = "";
+          break;
+        }
+        flushCurrent();
+        continue;
+      }
+      if (remaining.length <= available) {
+        current += remaining;
+        chunkHasContent = true;
+        break;
+      }
+      const splitAt = findTelegramHtmlSafeSplitIndex(remaining, available);
+      current += remaining.slice(0, splitAt);
+      chunkHasContent = true;
+      remaining = remaining.slice(splitAt);
+      flushCurrent();
+    }
+  };
+
+  resetCurrent();
+  HTML_TAG_PATTERN.lastIndex = 0;
+  let lastIndex = 0;
+  let match: RegExpExecArray | null;
+  while ((match = HTML_TAG_PATTERN.exec(html)) !== null) {
+    const tagStart = match.index;
+    const tagEnd = HTML_TAG_PATTERN.lastIndex;
+    appendText(html.slice(lastIndex, tagStart));
+
+    const rawTag = match[0];
+    const isClosing = match[1] === "</";
+    const tagName = match[2].toLowerCase();
+    const isSelfClosing =
+      !isClosing &&
+      (TELEGRAM_SELF_CLOSING_HTML_TAGS.has(tagName) || rawTag.trimEnd().endsWith("/>"));
+
+    if (!isClosing) {
+      const nextCloseLength = isSelfClosing ? 0 : `</${tagName}>`.length;
+      if (
+        chunkHasContent &&
+        current.length +
+          rawTag.length +
+          buildTelegramHtmlCloseSuffixLength(openTags) +
+          nextCloseLength >
+          normalizedLimit
+      ) {
+        flushCurrent();
+      }
+    }
+
+    current += rawTag;
+    chunkHasContent = true;
+    if (isClosing) {
+      popTelegramHtmlTag(openTags, tagName);
+    } else if (!isSelfClosing) {
+      openTags.push({
+        name: tagName,
+        openTag: rawTag,
+        closeTag: `</${tagName}>`,
+      });
+    }
+    lastIndex = tagEnd;
+  }
+
+  appendText(html.slice(lastIndex));
+  flushCurrent();
+  return chunks.length > 0 ? chunks : [html];
+}
+
 function splitTelegramChunkByHtmlLimit(
   chunk: MarkdownIR,
   htmlLimit: number,

src/telegram/send.test.ts

@@ -1257,6 +1257,37 @@ describe("sendMessageTelegram", () => {
       expect.objectContaining({ maxBytes: 42 * 1024 * 1024 }),
     );
   });
+
+  it("chunks long html-mode text and keeps buttons on the last chunk only", async () => {
+    const chatId = "123";
+    const htmlText = `<b>${"A".repeat(5000)}</b>`;
+
+    const sendMessage = vi
+      .fn()
+      .mockResolvedValueOnce({ message_id: 90, chat: { id: chatId } })
+      .mockResolvedValueOnce({ message_id: 91, chat: { id: chatId } });
+    const api = { sendMessage } as unknown as { sendMessage: typeof sendMessage };
+
+    const res = await sendMessageTelegram(chatId, htmlText, {
+      token: "tok",
+      api,
+      textMode: "html",
+      buttons: [[{ text: "OK", callback_data: "ok" }]],
+    });
+
+    expect(sendMessage).toHaveBeenCalledTimes(2);
+    const firstCall = sendMessage.mock.calls[0];
+    const secondCall = sendMessage.mock.calls[1];
+    expect(firstCall).toBeDefined();
+    expect(secondCall).toBeDefined();
+    expect((firstCall[1] as string).length).toBeLessThanOrEqual(4000);
+    expect((secondCall[1] as string).length).toBeLessThanOrEqual(4000);
+    expect(firstCall[2]?.reply_markup).toBeUndefined();
+    expect(secondCall[2]?.reply_markup).toEqual({
+      inline_keyboard: [[{ text: "OK", callback_data: "ok" }]],
+    });
+    expect(res.messageId).toBe("91");
+  });
 });
 
 describe("reactMessageTelegram", () => {

src/telegram/send.ts

@@ -26,7 +26,7 @@ import { buildTelegramThreadParams, buildTypingThreadParams } from "./bot/helper
 import type { TelegramInlineButtons } from "./button-types.js";
 import { splitTelegramCaption } from "./caption.js";
 import { resolveTelegramFetch } from "./fetch.js";
-import { renderTelegramHtmlText } from "./format.js";
+import { renderTelegramHtmlText, splitTelegramHtmlChunks } from "./format.js";
 import { isRecoverableTelegramNetworkError, isSafeToRetrySendError } from "./network-errors.js";
 import { makeProxyFetch } from "./proxy.js";
 import { recordSentMessage } from "./sent-message-cache.js";
@@ -600,13 +600,14 @@ export async function sendMessageTelegram(
     rawText: string,
     params?: Record<string, unknown>,
     fallbackText?: string,
+    preRenderedHtml?: string,
   ) => {
     return await withTelegramThreadFallback(
       params,
       "message",
       opts.verbose,
       async (effectiveParams, label) => {
-        const htmlText = renderHtmlText(rawText);
+        const htmlText = preRenderedHtml ?? renderHtmlText(rawText);
         const baseParams = effectiveParams ? { ...effectiveParams } : {};
         if (linkPreviewOptions) {
           baseParams.link_preview_options = linkPreviewOptions;
@@ -647,6 +648,47 @@ export async function sendMessageTelegram(
     );
   };
 
+  const buildTextParams = (isLastChunk: boolean) =>
+    hasThreadParams || (isLastChunk && replyMarkup)
+      ? {
+          ...threadParams,
+          ...(isLastChunk && replyMarkup ? { reply_markup: replyMarkup } : {}),
+        }
+      : undefined;
+
+  const sendChunkedText = async (
+    rawText: string,
+    context: string,
+  ): Promise<{ messageId: string; chatId: string }> => {
+    const chunks = splitTelegramHtmlChunks(rawText, 4000).map((chunk) => ({
+      rawText: chunk,
+      htmlText: chunk,
+      plainText: chunk,
+    }));
+
+    let lastMessageId = "";
+    let lastChatId = chatId;
+    for (let index = 0; index < chunks.length; index += 1) {
+      const chunk = chunks[index];
+      if (!chunk) {
+        continue;
+      }
+      const isLastChunk = index === chunks.length - 1;
+      const res = await sendTelegramText(
+        chunk.rawText,
+        buildTextParams(isLastChunk),
+        chunk.plainText,
+        chunk.htmlText,
+      );
+      const messageId = resolveTelegramMessageIdOrThrow(res, context);
+      recordSentMessage(chatId, messageId);
+      lastMessageId = String(messageId);
+      lastChatId = String(res?.chat?.id ?? chatId);
+    }
+
+    return { messageId: lastMessageId, chatId: lastChatId };
+  };
+
   if (mediaUrl) {
     const media = await loadWebMedia(
       mediaUrl,
@@ -801,21 +843,15 @@ export async function sendMessageTelegram(
     // If text was too long for a caption, send it as a separate follow-up message.
     // Use HTML conversion so markdown renders like captions.
     if (needsSeparateText && followUpText) {
-      const textParams =
-        hasThreadParams || replyMarkup
-          ? {
-              ...threadParams,
-              ...(replyMarkup ? { reply_markup: replyMarkup } : {}),
-            }
-          : undefined;
+      if (textMode === "html") {
+        const textResult = await sendChunkedText(followUpText, "text follow-up send");
+        return { messageId: textResult.messageId, chatId: resolvedChatId };
+      }
+      const textParams = buildTextParams(true);
       const textRes = await sendTelegramText(followUpText, textParams);
-      // Return the text message ID as the "main" message (it's the actual content).
       const textMessageId = resolveTelegramMessageIdOrThrow(textRes, "text follow-up send");
       recordSentMessage(chatId, textMessageId);
-      return {
-        messageId: String(textMessageId),
-        chatId: resolvedChatId,
-      };
+      return { messageId: String(textMessageId), chatId: resolvedChatId };
     }
 
     return { messageId: String(mediaMessageId), chatId: resolvedChatId };
@@ -824,22 +860,22 @@ export async function sendMessageTelegram(
   if (!text || !text.trim()) {
     throw new Error("Message must be non-empty for Telegram sends");
   }
-  const textParams =
-    hasThreadParams || replyMarkup
-      ? {
-          ...threadParams,
-          ...(replyMarkup ? { reply_markup: replyMarkup } : {}),
-        }
-      : undefined;
-  const res = await sendTelegramText(text, textParams, opts.plainText);
-  const messageId = resolveTelegramMessageIdOrThrow(res, "text send");
-  recordSentMessage(chatId, messageId);
+  let textResult: { messageId: string; chatId: string };
+  if (textMode === "html") {
+    textResult = await sendChunkedText(text, "text send");
+  } else {
+    const textParams = buildTextParams(true);
+    const res = await sendTelegramText(text, textParams, opts.plainText);
+    const messageId = resolveTelegramMessageIdOrThrow(res, "text send");
+    recordSentMessage(chatId, messageId);
+    textResult = { messageId: String(messageId), chatId: String(res?.chat?.id ?? chatId) };
+  }
   recordChannelActivity({
     channel: "telegram",
     accountId: account.accountId,
     direction: "outbound",
   });
-  return { messageId: String(messageId), chatId: String(res?.chat?.id ?? chatId) };
+  return textResult;
 }
 
 export async function sendTypingTelegram(