fix: preserve telegram html fallback

src/telegram/format.test.ts

@@ -125,6 +125,12 @@ describe("markdownToTelegramHtml", () => {
     expect(() => splitTelegramHtmlChunks(`A&${"B".repeat(20)}`, 4)).toThrow(/leading entity/i);
   });
 
+  it("treats malformed leading ampersands as plain text when chunking html", () => {
+    const chunks = splitTelegramHtmlChunks(`&${"A".repeat(5000)}`, 4000);
+    expect(chunks.length).toBeGreaterThan(1);
+    expect(chunks.every((chunk) => chunk.length <= 4000)).toBe(true);
+  });
+
   it("fails loudly when tag overhead leaves no room for text", () => {
     expect(() => splitTelegramHtmlChunks("<b><i><u>x</u></i></b>", 10)).toThrow(/tag overhead/i);
   });

src/telegram/format.ts

@@ -265,6 +265,50 @@ function buildTelegramHtmlCloseSuffixLength(tags: TelegramHtmlTag[]): number {
   return tags.reduce((total, tag) => total + tag.closeTag.length, 0);
 }
 
+function findTelegramHtmlEntityEnd(text: string, start: number): number {
+  if (text[start] !== "&") {
+    return -1;
+  }
+  let index = start + 1;
+  if (index >= text.length) {
+    return -1;
+  }
+  if (text[index] === "#") {
+    index += 1;
+    if (index >= text.length) {
+      return -1;
+    }
+    const isHex = text[index] === "x" || text[index] === "X";
+    if (isHex) {
+      index += 1;
+      const hexStart = index;
+      while (/[0-9A-Fa-f]/.test(text[index] ?? "")) {
+        index += 1;
+      }
+      if (index === hexStart) {
+        return -1;
+      }
+    } else {
+      const digitStart = index;
+      while (/[0-9]/.test(text[index] ?? "")) {
+        index += 1;
+      }
+      if (index === digitStart) {
+        return -1;
+      }
+    }
+  } else {
+    const nameStart = index;
+    while (/[A-Za-z0-9]/.test(text[index] ?? "")) {
+      index += 1;
+    }
+    if (index === nameStart) {
+      return -1;
+    }
+  }
+  return text[index] === ";" ? index : -1;
+}
+
 function findTelegramHtmlSafeSplitIndex(text: string, maxLength: number): number {
   if (text.length <= maxLength) {
     return text.length;
@@ -278,6 +322,10 @@ function findTelegramHtmlSafeSplitIndex(text: string, maxLength: number): number
   if (lastAmpersand < lastSemicolon) {
     return normalizedMaxLength;
   }
+  const entityEnd = findTelegramHtmlEntityEnd(text, lastAmpersand);
+  if (entityEnd === -1 || entityEnd < normalizedMaxLength) {
+    return normalizedMaxLength;
+  }
   return lastAmpersand;
 }
 

src/telegram/send.test.ts

@@ -1317,6 +1317,36 @@ describe("sendMessageTelegram", () => {
     expect(plainFallbackCalls.every((call) => !String(call?.[1] ?? "").includes("<"))).toBe(true);
     expect(res.messageId).toBe("91");
   });
+
+  it("keeps malformed leading ampersands on the chunked plain-text fallback path", async () => {
+    const chatId = "123";
+    const htmlText = `&${"A".repeat(5000)}`;
+    const plainText = "fallback!!";
+    const parseErr = new Error(
+      "400: Bad Request: can't parse entities: Can't find end of the entity starting at byte offset 0",
+    );
+    const sendMessage = vi
+      .fn()
+      .mockRejectedValueOnce(parseErr)
+      .mockResolvedValueOnce({ message_id: 92, chat: { id: chatId } })
+      .mockRejectedValueOnce(parseErr)
+      .mockResolvedValueOnce({ message_id: 93, chat: { id: chatId } });
+    const api = { sendMessage } as unknown as { sendMessage: typeof sendMessage };
+
+    const res = await sendMessageTelegram(chatId, htmlText, {
+      token: "tok",
+      api,
+      textMode: "html",
+      plainText,
+    });
+
+    expect(sendMessage).toHaveBeenCalledTimes(4);
+    expect(String(sendMessage.mock.calls[0]?.[1] ?? "")).toMatch(/^&/);
+    const plainFallbackCalls = [sendMessage.mock.calls[1], sendMessage.mock.calls[3]];
+    expect(plainFallbackCalls.map((call) => String(call?.[1] ?? "")).join("")).toBe(plainText);
+    expect(plainFallbackCalls.every((call) => String(call?.[1] ?? "").length > 0)).toBe(true);
+    expect(res.messageId).toBe("93");
+  });
 });
 
 describe("reactMessageTelegram", () => {

src/telegram/send.ts

@@ -108,24 +108,30 @@ function resolveTelegramMessageIdOrThrow(
   throw new Error(`Telegram ${context} returned no message_id`);
 }
 
+function splitTelegramPlainTextChunks(text: string, limit: number): string[] {
+  if (!text) {
+    return [];
+  }
+  const normalizedLimit = Math.max(1, Math.floor(limit));
+  const chunks: string[] = [];
+  for (let start = 0; start < text.length; start += normalizedLimit) {
+    chunks.push(text.slice(start, start + normalizedLimit));
+  }
+  return chunks;
+}
+
 function splitTelegramPlainTextFallback(text: string, chunkCount: number, limit: number): string[] {
   if (!text) {
     return [];
   }
   const normalizedLimit = Math.max(1, Math.floor(limit));
-  if (chunkCount <= 1 || text.length <= normalizedLimit) {
-    return [text];
-  }
-  if (text.length > chunkCount * normalizedLimit) {
-    const chunks: string[] = [];
-    for (let start = 0; start < text.length; start += normalizedLimit) {
-      chunks.push(text.slice(start, start + normalizedLimit));
-    }
-    return chunks;
+  const fixedChunks = splitTelegramPlainTextChunks(text, normalizedLimit);
+  if (chunkCount <= 1 || fixedChunks.length >= chunkCount) {
+    return fixedChunks;
   }
   const chunks: string[] = [];
   let offset = 0;
-  for (let index = 0; index < chunkCount && offset < text.length; index += 1) {
+  for (let index = 0; index < chunkCount; index += 1) {
     const remainingChars = text.length - offset;
     const remainingChunks = chunkCount - index;
     const nextChunkLength =
@@ -686,14 +692,65 @@ export async function sendMessageTelegram(
         }
       : undefined;
 
+  const sendPlainChunkedText = async (
+    plainText: string,
+    context: string,
+  ): Promise<{ messageId: string; chatId: string }> => {
+    const chunks = splitTelegramPlainTextChunks(plainText, 4000);
+    let lastMessageId = "";
+    let lastChatId = chatId;
+    for (let index = 0; index < chunks.length; index += 1) {
+      const chunk = chunks[index];
+      if (!chunk) {
+        continue;
+      }
+      const res = await withTelegramThreadFallback(
+        buildTextParams(index === chunks.length - 1),
+        "message",
+        opts.verbose,
+        async (effectiveParams, label) => {
+          const params = effectiveParams ? { ...effectiveParams } : {};
+          if (linkPreviewOptions) {
+            params.link_preview_options = linkPreviewOptions;
+          }
+          const hasParams = Object.keys(params).length > 0;
+          return await requestWithChatNotFound(
+            () =>
+              hasParams
+                ? api.sendMessage(chatId, chunk, params as Parameters<typeof api.sendMessage>[2])
+                : api.sendMessage(chatId, chunk),
+            label,
+          );
+        },
+      );
+      const messageId = resolveTelegramMessageIdOrThrow(res, context);
+      recordSentMessage(chatId, messageId);
+      lastMessageId = String(messageId);
+      lastChatId = String(res?.chat?.id ?? chatId);
+    }
+    return { messageId: lastMessageId, chatId: lastChatId };
+  };
+
   const sendChunkedText = async (
     rawText: string,
     context: string,
   ): Promise<{ messageId: string; chatId: string }> => {
-    const htmlChunks = splitTelegramHtmlChunks(rawText, 4000);
-    const plainTextChunks = opts.plainText
-      ? splitTelegramPlainTextFallback(opts.plainText, htmlChunks.length, 4000)
-      : [];
+    let htmlChunks: string[];
+    try {
+      htmlChunks = splitTelegramHtmlChunks(rawText, 4000);
+    } catch (error) {
+      logVerbose(
+        `telegram ${context} failed HTML chunk planning, retrying as plain text: ${formatErrorMessage(
+          error,
+        )}`,
+      );
+      return await sendPlainChunkedText(opts.plainText ?? rawText, context);
+    }
+    const plainTextChunks = splitTelegramPlainTextFallback(
+      opts.plainText ?? rawText,
+      htmlChunks.length,
+      4000,
+    );
     const chunks = htmlChunks.map((chunk, index) => ({
       rawText: chunk,
       htmlText: chunk,