fix: extend discord thread parent fallback coverage (#24897) (thanks @z-x-yang)

src/discord/monitor/threading.parent-info.test.ts

@@ -44,4 +44,63 @@ describe("resolveDiscordThreadParentInfo", () => {
       type: ChannelType.GuildText,
     });
   });
+
+  it("does not fetch thread info when parentId is already present", async () => {
+    const fetchChannel = vi.fn(async (channelId: string) => {
+      if (channelId === "parent-1") {
+        return {
+          id: "parent-1",
+          type: ChannelType.GuildText,
+          name: "parent-name",
+        };
+      }
+      return null;
+    });
+
+    const client = { fetchChannel } as unknown as import("@buape/carbon").Client;
+    const result = await resolveDiscordThreadParentInfo({
+      client,
+      threadChannel: {
+        id: "thread-1",
+        parentId: "parent-1",
+      },
+      channelInfo: null,
+    });
+
+    expect(fetchChannel).toHaveBeenCalledTimes(1);
+    expect(fetchChannel).toHaveBeenCalledWith("parent-1");
+    expect(result).toEqual({
+      id: "parent-1",
+      name: "parent-name",
+      type: ChannelType.GuildText,
+    });
+  });
+
+  it("returns empty parent info when fallback thread lookup has no parentId", async () => {
+    const fetchChannel = vi.fn(async (channelId: string) => {
+      if (channelId === "thread-1") {
+        return {
+          id: "thread-1",
+          type: ChannelType.PublicThread,
+          name: "thread-name",
+          parentId: undefined,
+        };
+      }
+      return null;
+    });
+
+    const client = { fetchChannel } as unknown as import("@buape/carbon").Client;
+    const result = await resolveDiscordThreadParentInfo({
+      client,
+      threadChannel: {
+        id: "thread-1",
+        parentId: undefined,
+      },
+      channelInfo: null,
+    });
+
+    expect(fetchChannel).toHaveBeenCalledTimes(1);
+    expect(fetchChannel).toHaveBeenCalledWith("thread-1");
+    expect(result).toEqual({});
+  });
 });