feat(telegram): expose parseMode config option

.changeset/telegram-parse-mode-config.md

@@ -0,0 +1,7 @@
+---
+"@chat-adapter/telegram": minor
+---
+
+Add `parseMode` config option to `TelegramAdapterConfig`. Allows callers to opt
+into `MarkdownV2`, `HTML`, or disable `parse_mode` entirely (`"none"`). Defaults
+to `"Markdown"` for backward compatibility.

packages/adapter-telegram/src/index.test.ts

@@ -976,6 +976,90 @@ describe("TelegramAdapter", () => {
     expect(sendMessageBody.parse_mode).toBe("Markdown");
   });
 
+  it("honors parseMode config option for markdown messages", async () => {
+    for (const mode of ["MarkdownV2", "HTML"] as const) {
+      mockFetch
+        .mockResolvedValueOnce(
+          telegramOk({
+            id: 999,
+            is_bot: true,
+            first_name: "Bot",
+            username: "mybot",
+          })
+        )
+        .mockResolvedValueOnce(telegramOk(sampleMessage()));
+
+      const adapter = createTelegramAdapter({
+        botToken: "token",
+        mode: "webhook",
+        logger: mockLogger,
+        userName: "mybot",
+        parseMode: mode,
+      });
+
+      await adapter.initialize(createMockChat());
+
+      await adapter.postMessage("telegram:123", {
+        markdown: "**bold**",
+      });
+
+      const sendMessageBody = JSON.parse(
+        String(
+          (mockFetch.mock.calls[mockFetch.mock.calls.length - 1]?.[1] as RequestInit).body
+        )
+      ) as { parse_mode?: string };
+
+      expect(sendMessageBody.parse_mode).toBe(mode);
+      mockFetch.mockClear();
+    }
+  });
+
+  it("omits parse_mode when parseMode is 'none'", async () => {
+    mockFetch
+      .mockResolvedValueOnce(
+        telegramOk({
+          id: 999,
+          is_bot: true,
+          first_name: "Bot",
+          username: "mybot",
+        })
+      )
+      .mockResolvedValueOnce(telegramOk(sampleMessage()));
+
+    const adapter = createTelegramAdapter({
+      botToken: "token",
+      mode: "webhook",
+      logger: mockLogger,
+      userName: "mybot",
+      parseMode: "none",
+    });
+
+    await adapter.initialize(createMockChat());
+
+    await adapter.postMessage("telegram:123", {
+      markdown: "**bold**",
+    });
+
+    const sendMessageBody = JSON.parse(
+      String((mockFetch.mock.calls[1]?.[1] as RequestInit).body)
+    ) as { parse_mode?: string };
+
+    expect(sendMessageBody.parse_mode).toBeUndefined();
+  });
+
+  it("rejects invalid parseMode values", () => {
+    expect(() =>
+      createTelegramAdapter({
+        botToken: "token",
+        mode: "webhook",
+        logger: mockLogger,
+        userName: "mybot",
+        // @ts-expect-error testing runtime validation
+        parseMode: "Bogus",
+      })
+    ).toThrow(/Invalid parseMode/);
+  });
+
   it("posts cards with inline keyboard buttons", async () => {
     mockFetch
       .mockResolvedValueOnce(

packages/adapter-telegram/src/index.ts

@@ -49,6 +49,7 @@ import type {
   TelegramInlineKeyboardMarkup,
   TelegramLongPollingConfig,
   TelegramMessage,
+  TelegramParseMode,
   TelegramMessageEntity,
   TelegramMessageReactionUpdated,
   TelegramRawMessage,
@@ -64,7 +65,6 @@ const TELEGRAM_MESSAGE_LIMIT = 4096;
 const TELEGRAM_CAPTION_LIMIT = 1024;
 const TELEGRAM_SECRET_TOKEN_HEADER = "x-telegram-bot-api-secret-token";
 const MESSAGE_ID_PATTERN = /^([^:]+):(\d+)$/;
-const TELEGRAM_MARKDOWN_PARSE_MODE = "Markdown";
 const trimTrailingSlashes = (url: string): string => {
   let end = url.length;
   while (end > 0 && url[end - 1] === "/") {
@@ -210,6 +210,7 @@ export class TelegramAdapter
   private readonly hasExplicitUserName: boolean;
   private readonly mode: TelegramAdapterMode;
   private readonly longPolling?: TelegramLongPollingConfig;
+  private readonly parseMode: TelegramParseMode;
   private _runtimeMode: TelegramRuntimeMode = "webhook";
   private pollingAbortController: AbortController | null = null;
   private pollingTask: Promise<void> | null = null;
@@ -254,13 +255,23 @@ export class TelegramAdapter
     this.hasExplicitUserName = Boolean(userName);
     this.mode = config.mode ?? "auto";
     this.longPolling = config.longPolling;
+    this.parseMode = config.parseMode ?? "Markdown";
 
     if (!["auto", "webhook", "polling"].includes(this.mode)) {
       throw new ValidationError(
         "telegram",
         `Invalid mode: ${this.mode}. Expected "auto", "webhook", or "polling".`
       );
     }
+
+    if (
+      !["Markdown", "MarkdownV2", "HTML", "none"].includes(this.parseMode)
+    ) {
+      throw new ValidationError(
+        "telegram",
+        `Invalid parseMode: ${this.parseMode}. Expected "Markdown", "MarkdownV2", "HTML", or "none".`
+      );
+    }
   }
 
   async initialize(chat: ChatInstance): Promise<void> {
@@ -1503,7 +1514,8 @@ export class TelegramAdapter
   ): string | undefined {
     const hasMarkdown =
       typeof message === "object" && message !== null && "markdown" in message;
-    return card || hasMarkdown ? TELEGRAM_MARKDOWN_PARSE_MODE : undefined;
+    if (!card && !hasMarkdown) return undefined;
+    return this.parseMode === "none" ? undefined : this.parseMode;
   }
 
   private truncateMessage(text: string): string {

packages/adapter-telegram/src/types.ts

@@ -23,6 +23,20 @@ export interface TelegramAdapterConfig {
    * - polling: polling-only mode
    */
   mode?: TelegramAdapterMode;
+  /**
+   * Telegram parse_mode used when sending messages with a `markdown` field
+   * or a card. See https://core.telegram.org/bots/api#formatting-options.
+   * - "Markdown" (default): legacy Markdown — kept for backward compatibility
+   *   with prior behavior. Telegram considers this mode legacy and it has no
+   *   escape support.
+   * - "MarkdownV2": current Telegram markdown with full escape support.
+   * - "HTML": HTML formatting.
+   * - "none": omit parse_mode entirely (send as plain text). Useful as a
+   *   safety valve when the upstream markdown converter produces output
+   *   Telegram cannot parse.
+   * @default "Markdown"
+   */
+  parseMode?: TelegramParseMode;
   /** Optional webhook secret token checked against x-telegram-bot-api-secret-token. Defaults to TELEGRAM_WEBHOOK_SECRET_TOKEN env var. */
   secretToken?: string;
   /** Override bot username (optional). Defaults to TELEGRAM_BOT_USERNAME env var. */
@@ -31,6 +45,8 @@ export interface TelegramAdapterConfig {
 
 export type TelegramAdapterMode = "auto" | "webhook" | "polling";
 
+export type TelegramParseMode = "Markdown" | "MarkdownV2" | "HTML" | "none";
+
 /**
  * Telegram long-polling configuration.
  * @see https://core.telegram.org/bots/api#getupdates