fix(telegram): preserve explicit empty media captions (#116984)

Co-authored-by: Peter Steinberger <steipete@macos.shared>

extensions/telegram/src/action-runtime.test.ts

@@ -1854,21 +1854,26 @@ describe("handleTelegramAction", () => {
     expect(requireRecord(call[3], "reply markup edit options").token).toBe("tok");
   });
 
-  it("uses Telegram caption edits when editMessage receives a caption", async () => {
+  it.each([
+    { description: "non-empty", caption: "Updated caption", richMessages: false },
+    { description: "empty", caption: "", richMessages: false },
+    { description: "non-empty rich", caption: "Updated caption", richMessages: true },
+    { description: "empty rich", caption: "", richMessages: true },
+  ])("uses Telegram caption edits for $description captions", async ({ caption, richMessages }) => {
     await handleTelegramAction(
       {
         action: "editMessage",
         chatId: "123456",
         messageId: 321,
-        caption: "Updated caption",
+        caption,
       },
-      telegramConfig(),
+      telegramConfig(richMessages ? { richMessages: true } : undefined),
     );
 
     const call = mockCall(editMessageTelegram, 0, "caption edit");
     expect(call[0]).toBe("123456");
     expect(call[1]).toBe(321);
-    expect(call[2]).toBe("Updated caption");
+    expect(call[2]).toBe(caption);
     expect(requireRecord(call[3], "caption edit options").editMode).toBe("caption");
   });
 

extensions/telegram/src/action-runtime.ts

@@ -739,7 +739,8 @@ export async function handleTelegramAction(
     const content =
       readStringParam(params, "content", { allowEmpty: false }) ??
       readStringParam(params, "message", { allowEmpty: false });
-    const caption = readStringParam(params, "caption", { allowEmpty: false });
+    // Telegram treats an explicit empty caption as a request to remove it.
+    const caption = readStringParam(params, "caption", { allowEmpty: true });
     const buttons = resolveTelegramButtonsFromParams(params, undefined, {
       allowWebAppButtons: resolveTelegramTargetChatType(chatId ?? "") === "direct",
     });

extensions/telegram/src/send-caption-editing.test.ts

@@ -0,0 +1,49 @@
+import { describe, expect, it } from "vitest";
+import {
+  getTelegramSendTestMocks,
+  importTelegramSendModule,
+  installTelegramSendTestHooks,
+} from "./send.test-harness.js";
+
+installTelegramSendTestHooks();
+
+const { botApi, loadConfig } = getTelegramSendTestMocks();
+const { editMessageTelegram } = await importTelegramSendModule();
+
+describe("Telegram caption edits", () => {
+  it.each([
+    {
+      description: "non-empty plain",
+      caption: "Updated **caption**",
+      expected: "Updated <b>caption</b>",
+      richMessages: false,
+    },
+    { description: "empty plain", caption: "", expected: "", richMessages: false },
+    {
+      description: "non-empty rich",
+      caption: "Updated **caption**",
+      expected: "Updated <b>caption</b>",
+      richMessages: true,
+    },
+    { description: "empty rich", caption: "", expected: "", richMessages: true },
+  ])(
+    "preserves $description captions at the Bot API boundary",
+    async ({ caption, expected, richMessages }) => {
+      loadConfig.mockReturnValue({ channels: { telegram: { botToken: "tok", richMessages } } });
+      botApi.editMessageCaption.mockResolvedValue({ message_id: 321, chat: { id: "123456" } });
+
+      await editMessageTelegram("123456", 321, caption, {
+        cfg: { channels: { telegram: { botToken: "tok", richMessages } } },
+        token: "tok",
+        accountId: "default",
+        editMode: "caption",
+      });
+
+      expect(botApi.editMessageText).not.toHaveBeenCalled();
+      expect(botApi.editMessageCaption).toHaveBeenCalledWith("123456", 321, {
+        caption: expected,
+        parse_mode: "HTML",
+      });
+    },
+  );
+});