fix: read Slack thread replies for message reads (#1450) (#1450)

Co-authored-by: Peter Steinberger <steipete@gmail.com>
Co-authored-by: Rodrigo Uroz <rodrigouroz@users.noreply.github.com>

src/slack/actions.read.test.ts

@@ -0,0 +1,68 @@
+import { describe, expect, it, vi } from "vitest";
+
+import type { WebClient } from "@slack/web-api";
+
+import { readSlackMessages } from "./actions.js";
+
+function createClient() {
+  return {
+    conversations: {
+      replies: vi.fn(async () => ({ messages: [], has_more: false })),
+      history: vi.fn(async () => ({ messages: [], has_more: false })),
+    },
+  } as unknown as WebClient & {
+    conversations: {
+      replies: ReturnType<typeof vi.fn>;
+      history: ReturnType<typeof vi.fn>;
+    };
+  };
+}
+
+describe("readSlackMessages", () => {
+  it("uses conversations.replies and drops the parent message", async () => {
+    const client = createClient();
+    client.conversations.replies.mockResolvedValueOnce({
+      messages: [{ ts: "171234.567" }, { ts: "171234.890" }, { ts: "171235.000" }],
+      has_more: true,
+    });
+
+    const result = await readSlackMessages("C1", {
+      client,
+      threadId: "171234.567",
+      token: "xoxb-test",
+    });
+
+    expect(client.conversations.replies).toHaveBeenCalledWith({
+      channel: "C1",
+      ts: "171234.567",
+      limit: undefined,
+      latest: undefined,
+      oldest: undefined,
+    });
+    expect(client.conversations.history).not.toHaveBeenCalled();
+    expect(result.messages.map((message) => message.ts)).toEqual(["171234.890", "171235.000"]);
+  });
+
+  it("uses conversations.history when threadId is missing", async () => {
+    const client = createClient();
+    client.conversations.history.mockResolvedValueOnce({
+      messages: [{ ts: "1" }],
+      has_more: false,
+    });
+
+    const result = await readSlackMessages("C1", {
+      client,
+      limit: 20,
+      token: "xoxb-test",
+    });
+
+    expect(client.conversations.history).toHaveBeenCalledWith({
+      channel: "C1",
+      limit: 20,
+      latest: undefined,
+      oldest: undefined,
+    });
+    expect(client.conversations.replies).not.toHaveBeenCalled();
+    expect(result.messages.map((message) => message.ts)).toEqual(["1"]);
+  });
+});

src/slack/actions.ts

@@ -186,9 +186,29 @@ export async function readSlackMessages(
     limit?: number;
     before?: string;
     after?: string;
+    threadId?: string;
   } = {},
 ): Promise<{ messages: SlackMessageSummary[]; hasMore: boolean }> {
   const client = await getClient(opts);
+
+  // Use conversations.replies for thread messages, conversations.history for channel messages.
+  if (opts.threadId) {
+    const result = await client.conversations.replies({
+      channel: channelId,
+      ts: opts.threadId,
+      limit: opts.limit,
+      latest: opts.before,
+      oldest: opts.after,
+    });
+    return {
+      // conversations.replies includes the parent message; drop it for replies-only reads.
+      messages: (result.messages ?? []).filter(
+        (message) => (message as SlackMessageSummary)?.ts !== opts.threadId,
+      ) as SlackMessageSummary[],
+      hasMore: Boolean(result.has_more),
+    };
+  }
+
   const result = await client.conversations.history({
     channel: channelId,
     limit: opts.limit,