feat(slack): add draft preview cleanup lifecycle

src/slack/draft-stream.test.ts

@@ -103,4 +103,54 @@ describe("createSlackDraftStream", () => {
     expect(edit).not.toHaveBeenCalled();
     expect(warn).toHaveBeenCalledTimes(1);
   });
+
+  it("clear removes preview message when one exists", async () => {
+    const send = vi.fn(async () => ({
+      channelId: "C123",
+      messageId: "111.222",
+    }));
+    const edit = vi.fn(async () => {});
+    const remove = vi.fn(async () => {});
+    const stream = createSlackDraftStream({
+      target: "channel:C123",
+      token: "xoxb-test",
+      throttleMs: 250,
+      send,
+      edit,
+      remove,
+    });
+
+    stream.update("hello");
+    await stream.flush();
+    await stream.clear();
+
+    expect(remove).toHaveBeenCalledTimes(1);
+    expect(remove).toHaveBeenCalledWith("C123", "111.222", {
+      token: "xoxb-test",
+      accountId: undefined,
+    });
+    expect(stream.messageId()).toBeUndefined();
+    expect(stream.channelId()).toBeUndefined();
+  });
+
+  it("clear is a no-op when no preview message exists", async () => {
+    const send = vi.fn(async () => ({
+      channelId: "C123",
+      messageId: "111.222",
+    }));
+    const edit = vi.fn(async () => {});
+    const remove = vi.fn(async () => {});
+    const stream = createSlackDraftStream({
+      target: "channel:C123",
+      token: "xoxb-test",
+      throttleMs: 250,
+      send,
+      edit,
+      remove,
+    });
+
+    await stream.clear();
+
+    expect(remove).not.toHaveBeenCalled();
+  });
 });