feat(slack): stream partial replies via draft message updates

src/slack/draft-stream.test.ts

@@ -0,0 +1,106 @@
+import { describe, expect, it, vi } from "vitest";
+import { createSlackDraftStream } from "./draft-stream.js";
+
+describe("createSlackDraftStream", () => {
+  it("sends the first update and edits subsequent updates", async () => {
+    const send = vi.fn(async () => ({
+      channelId: "C123",
+      messageId: "111.222",
+    }));
+    const edit = vi.fn(async () => {});
+    const stream = createSlackDraftStream({
+      target: "channel:C123",
+      token: "xoxb-test",
+      throttleMs: 250,
+      send,
+      edit,
+    });
+
+    stream.update("hello");
+    await stream.flush();
+    stream.update("hello world");
+    await stream.flush();
+
+    expect(send).toHaveBeenCalledTimes(1);
+    expect(edit).toHaveBeenCalledTimes(1);
+    expect(edit).toHaveBeenCalledWith("C123", "111.222", "hello world", {
+      token: "xoxb-test",
+      accountId: undefined,
+    });
+  });
+
+  it("does not send duplicate text", async () => {
+    const send = vi.fn(async () => ({
+      channelId: "C123",
+      messageId: "111.222",
+    }));
+    const edit = vi.fn(async () => {});
+    const stream = createSlackDraftStream({
+      target: "channel:C123",
+      token: "xoxb-test",
+      throttleMs: 250,
+      send,
+      edit,
+    });
+
+    stream.update("same");
+    await stream.flush();
+    stream.update("same");
+    await stream.flush();
+
+    expect(send).toHaveBeenCalledTimes(1);
+    expect(edit).toHaveBeenCalledTimes(0);
+  });
+
+  it("supports forceNewMessage for subsequent assistant messages", async () => {
+    const send = vi
+      .fn()
+      .mockResolvedValueOnce({ channelId: "C123", messageId: "111.222" })
+      .mockResolvedValueOnce({ channelId: "C123", messageId: "333.444" });
+    const edit = vi.fn(async () => {});
+    const stream = createSlackDraftStream({
+      target: "channel:C123",
+      token: "xoxb-test",
+      throttleMs: 250,
+      send,
+      edit,
+    });
+
+    stream.update("first");
+    await stream.flush();
+    stream.forceNewMessage();
+    stream.update("second");
+    await stream.flush();
+
+    expect(send).toHaveBeenCalledTimes(2);
+    expect(edit).toHaveBeenCalledTimes(0);
+    expect(stream.messageId()).toBe("333.444");
+  });
+
+  it("stops when text exceeds max chars", async () => {
+    const send = vi.fn(async () => ({
+      channelId: "C123",
+      messageId: "111.222",
+    }));
+    const edit = vi.fn(async () => {});
+    const warn = vi.fn();
+    const stream = createSlackDraftStream({
+      target: "channel:C123",
+      token: "xoxb-test",
+      maxChars: 5,
+      throttleMs: 250,
+      send,
+      edit,
+      warn,
+    });
+
+    stream.update("123456");
+    await stream.flush();
+    stream.update("ok");
+    await stream.flush();
+
+    expect(send).not.toHaveBeenCalled();
+    expect(edit).not.toHaveBeenCalled();
+    expect(warn).toHaveBeenCalledTimes(1);
+  });
+});