fix: harden slack debounce key routing and ordering (#31951) (thanks @scoootscooob)

src/slack/monitor/message-handler.test.ts

@@ -2,6 +2,7 @@ import { beforeEach, describe, expect, it, vi } from "vitest";
 import { createSlackMessageHandler } from "./message-handler.js";
 
 const enqueueMock = vi.fn(async (_entry: unknown) => {});
+const flushKeyMock = vi.fn(async (_key: string) => {});
 const resolveThreadTsMock = vi.fn(async ({ message }: { message: Record<string, unknown> }) => ({
   ...message,
 }));
@@ -10,6 +11,7 @@ vi.mock("../../auto-reply/inbound-debounce.js", () => ({
   resolveInboundDebounceMs: () => 10,
   createInboundDebouncer: () => ({
     enqueue: (entry: unknown) => enqueueMock(entry),
+    flushKey: (key: string) => flushKeyMock(key),
   }),
 }));
 
@@ -37,6 +39,7 @@ function createContext(overrides?: {
 describe("createSlackMessageHandler", () => {
   beforeEach(() => {
     enqueueMock.mockClear();
+    flushKeyMock.mockClear();
     resolveThreadTsMock.mockClear();
   });
 
@@ -113,4 +116,38 @@ describe("createSlackMessageHandler", () => {
     expect(resolveThreadTsMock).toHaveBeenCalledTimes(1);
     expect(enqueueMock).toHaveBeenCalledTimes(1);
   });
+
+  it("flushes pending top-level buffered keys before immediate non-debounce follow-ups", async () => {
+    const handler = createSlackMessageHandler({
+      ctx: createContext(),
+      account: { accountId: "default" } as Parameters<
+        typeof createSlackMessageHandler
+      >[0]["account"],
+    });
+
+    await handler(
+      {
+        type: "message",
+        channel: "C111",
+        user: "U111",
+        ts: "1709000000.000100",
+        text: "first buffered text",
+      } as never,
+      { source: "message" },
+    );
+    await handler(
+      {
+        type: "message",
+        subtype: "file_share",
+        channel: "C111",
+        user: "U111",
+        ts: "1709000000.000200",
+        text: "file follows",
+        files: [{ id: "F1" }],
+      } as never,
+      { source: "message" },
+    );
+
+    expect(flushKeyMock).toHaveBeenCalledWith("slack:default:C111:1709000000.000100:U111");
+  });
 });