Fix Discord auto-thread attempting to thread in Forum/Media channels\n\nCreating threads on messages within Forum/Media channels is often redundant\nor invalid (as messages are already posts). This prevents API errors and spam.\n\nFix: Check channel type before attempting auto-thread creation.

src/discord/monitor/message-handler.process.ts

@@ -483,6 +483,7 @@ export async function processDiscordMessage(ctx: DiscordMessagePreflightContext)
     isGuildMessage,
     channelConfig,
     threadChannel,
+    channelType: channelInfo?.type,
     baseText: baseText ?? "",
     combinedBody,
     replyToMode,

src/discord/monitor/threading.auto-thread.test.ts

@@ -0,0 +1,54 @@
+import { describe, it, expect, vi } from "vitest";
+import { ChannelType } from "@buape/carbon";
+import { maybeCreateDiscordAutoThread } from "./threading.js";
+
+describe("maybeCreateDiscordAutoThread", () => {
+  const mockClient = { rest: { post: vi.fn(), get: vi.fn() } } as any;
+  const mockMessage = { id: "msg1", timestamp: "123" } as any;
+
+  it("skips auto-thread if channelType is GuildForum", async () => {
+    const result = await maybeCreateDiscordAutoThread({
+      client: mockClient,
+      message: mockMessage,
+      messageChannelId: "forum1",
+      isGuildMessage: true,
+      channelConfig: { autoThread: true },
+      channelType: ChannelType.GuildForum,
+      baseText: "test",
+      combinedBody: "test",
+    });
+    expect(result).toBeUndefined();
+    expect(mockClient.rest.post).not.toHaveBeenCalled();
+  });
+
+  it("skips auto-thread if channelType is GuildMedia", async () => {
+    const result = await maybeCreateDiscordAutoThread({
+      client: mockClient,
+      message: mockMessage,
+      messageChannelId: "media1",
+      isGuildMessage: true,
+      channelConfig: { autoThread: true },
+      channelType: ChannelType.GuildMedia,
+      baseText: "test",
+      combinedBody: "test",
+    });
+    expect(result).toBeUndefined();
+    expect(mockClient.rest.post).not.toHaveBeenCalled();
+  });
+
+  it("creates auto-thread if channelType is GuildText", async () => {
+    mockClient.rest.post.mockResolvedValueOnce({ id: "thread1" });
+    const result = await maybeCreateDiscordAutoThread({
+      client: mockClient,
+      message: mockMessage,
+      messageChannelId: "text1",
+      isGuildMessage: true,
+      channelConfig: { autoThread: true },
+      channelType: ChannelType.GuildText,
+      baseText: "test",
+      combinedBody: "test",
+    });
+    expect(result).toBe("thread1");
+    expect(mockClient.rest.post).toHaveBeenCalled();
+  });
+});

src/discord/monitor/threading.ts

@@ -298,6 +298,7 @@ export async function resolveDiscordAutoThreadReplyPlan(params: {
   isGuildMessage: boolean;
   channelConfig?: DiscordChannelConfigResolved | null;
   threadChannel?: DiscordThreadChannel | null;
+  channelType?: ChannelType;
   baseText: string;
   combinedBody: string;
   replyToMode: ReplyToMode;
@@ -320,6 +321,7 @@ export async function resolveDiscordAutoThreadReplyPlan(params: {
     isGuildMessage: params.isGuildMessage,
     channelConfig: params.channelConfig,
     threadChannel: params.threadChannel,
+    channelType: params.channelType,
     baseText: params.baseText,
     combinedBody: params.combinedBody,
   });
@@ -348,6 +350,7 @@ export async function maybeCreateDiscordAutoThread(params: {
   isGuildMessage: boolean;
   channelConfig?: DiscordChannelConfigResolved | null;
   threadChannel?: DiscordThreadChannel | null;
+  channelType?: ChannelType;
   baseText: string;
   combinedBody: string;
 }): Promise<string | undefined> {
@@ -360,6 +363,16 @@ export async function maybeCreateDiscordAutoThread(params: {
   if (params.threadChannel) {
     return undefined;
   }
+  // Avoid creating threads in channels that don't support it or are already forums
+  if (
+    params.channelType === ChannelType.GuildForum ||
+    params.channelType === ChannelType.GuildMedia ||
+    params.channelType === ChannelType.GuildVoice ||
+    params.channelType === ChannelType.GuildStageVoice
+  ) {
+    return undefined;
+  }
+
   const messageChannelId = (
     params.messageChannelId ||
     resolveDiscordMessageChannelId({