fix(discord): support forum channel thread-create (#10062)

* fix(discord): support forum channel thread-create

* fix: harden discord forum thread-create (#10062) (thanks @jarvis89757)

---------

Co-authored-by: Shakker <shakkerdroid@gmail.com>

src/discord/send.creates-thread.test.ts

@@ -1,5 +1,5 @@
 import { RateLimitError } from "@buape/carbon";
-import { Routes } from "discord-api-types/v10";
+import { ChannelType, Routes } from "discord-api-types/v10";
 import { beforeEach, describe, expect, it, vi } from "vitest";
 import {
   addRoleDiscord,
@@ -60,15 +60,64 @@ describe("sendMessageDiscord", () => {
   });
 
   it("creates a thread", async () => {
-    const { rest, postMock } = makeRest();
+    const { rest, getMock, postMock } = makeRest();
     postMock.mockResolvedValue({ id: "t1" });
     await createThreadDiscord("chan1", { name: "thread", messageId: "m1" }, { rest, token: "t" });
+    expect(getMock).not.toHaveBeenCalled();
     expect(postMock).toHaveBeenCalledWith(
       Routes.threads("chan1", "m1"),
       expect.objectContaining({ body: { name: "thread" } }),
     );
   });
 
+  it("creates forum threads with an initial message", async () => {
+    const { rest, getMock, postMock } = makeRest();
+    getMock.mockResolvedValue({ type: ChannelType.GuildForum });
+    postMock.mockResolvedValue({ id: "t1" });
+    await createThreadDiscord("chan1", { name: "thread" }, { rest, token: "t" });
+    expect(getMock).toHaveBeenCalledWith(Routes.channel("chan1"));
+    expect(postMock).toHaveBeenCalledWith(
+      Routes.threads("chan1"),
+      expect.objectContaining({
+        body: {
+          name: "thread",
+          message: { content: "thread" },
+        },
+      }),
+    );
+  });
+
+  it("creates media threads with provided content", async () => {
+    const { rest, getMock, postMock } = makeRest();
+    getMock.mockResolvedValue({ type: ChannelType.GuildMedia });
+    postMock.mockResolvedValue({ id: "t1" });
+    await createThreadDiscord(
+      "chan1",
+      { name: "thread", content: "initial forum post" },
+      { rest, token: "t" },
+    );
+    expect(postMock).toHaveBeenCalledWith(
+      Routes.threads("chan1"),
+      expect.objectContaining({
+        body: {
+          name: "thread",
+          message: { content: "initial forum post" },
+        },
+      }),
+    );
+  });
+
+  it("falls back when channel lookup is unavailable", async () => {
+    const { rest, getMock, postMock } = makeRest();
+    getMock.mockRejectedValue(new Error("lookup failed"));
+    postMock.mockResolvedValue({ id: "t1" });
+    await createThreadDiscord("chan1", { name: "thread" }, { rest, token: "t" });
+    expect(postMock).toHaveBeenCalledWith(
+      Routes.threads("chan1"),
+      expect.objectContaining({ body: { name: "thread" } }),
+    );
+  });
+
   it("lists active threads by guild", async () => {
     const { rest, getMock } = makeRest();
     getMock.mockResolvedValue({ threads: [] });

src/discord/send.messages.ts

@@ -1,5 +1,5 @@
-import type { APIMessage } from "discord-api-types/v10";
-import { Routes } from "discord-api-types/v10";
+import type { APIChannel, APIMessage } from "discord-api-types/v10";
+import { ChannelType, Routes } from "discord-api-types/v10";
 import type {
   DiscordMessageEdit,
   DiscordMessageQuery,
@@ -105,7 +105,26 @@ export async function createThreadDiscord(
   if (payload.autoArchiveMinutes) {
     body.auto_archive_duration = payload.autoArchiveMinutes;
   }
-  const route = Routes.threads(channelId, payload.messageId);
+  let channelType: ChannelType | undefined;
+  if (!payload.messageId) {
+    // Only detect channel kind for route-less thread creation.
+    // If this lookup fails, keep prior behavior and let Discord validate.
+    try {
+      const channel = (await rest.get(Routes.channel(channelId))) as APIChannel | null | undefined;
+      channelType = channel?.type;
+    } catch {
+      channelType = undefined;
+    }
+  }
+  const isForumLike =
+    channelType === ChannelType.GuildForum || channelType === ChannelType.GuildMedia;
+  if (isForumLike) {
+    const starterContent = payload.content?.trim() ? payload.content : payload.name;
+    body.message = { content: starterContent };
+  }
+  const route = payload.messageId
+    ? Routes.threads(channelId, payload.messageId)
+    : Routes.threads(channelId);
   return await rest.post(route, { body });
 }
 

src/discord/send.types.ts

@@ -71,6 +71,7 @@ export type DiscordThreadCreate = {
   messageId?: string;
   name: string;
   autoArchiveMinutes?: number;
+  content?: string;
 };
 
 export type DiscordThreadList = {