diff --git a/src/agents/tools/message-tool.ts b/src/agents/tools/message-tool.ts
index d0d8d5d8f..50c1f51d5 100644
--- a/src/agents/tools/message-tool.ts
+++ b/src/agents/tools/message-tool.ts
@@ -134,6 +134,14 @@ const MessageToolSchema = Type.Object({
 type MessageToolOptions = {
   agentAccountId?: string;
   config?: ClawdbotConfig;
+  /** Current channel ID for auto-threading (Slack). */
+  currentChannelId?: string;
+  /** Current thread timestamp for auto-threading (Slack). */
+  currentThreadTs?: string;
+  /** Reply-to mode for Slack auto-threading. */
+  replyToMode?: "off" | "first" | "all";
+  /** Mutable ref to track if a reply was sent (for "first" mode). */
+  hasRepliedRef?: { value: boolean };
 };
 
 function hasTelegramInlineButtons(cfg: ClawdbotConfig): boolean {
diff --git a/src/slack/actions.ts b/src/slack/actions.ts
index 9c2b2cc9e..c108ebe72 100644
--- a/src/slack/actions.ts
+++ b/src/slack/actions.ts
@@ -151,7 +151,6 @@ export async function sendSlackMessage(
     accountId: opts.accountId,
     token: opts.token,
     mediaUrl: opts.mediaUrl,
-    threadTs: opts.threadTs,
     client: opts.client,
     threadTs: opts.threadTs,
   });
diff --git a/src/slack/monitor.tool-result.test.ts b/src/slack/monitor.tool-result.test.ts
index d67fe25ab..387f81c73 100644
--- a/src/slack/monitor.tool-result.test.ts
+++ b/src/slack/monitor.tool-result.test.ts
@@ -601,8 +601,52 @@ describe("monitorSlackProvider tool results", () => {
     expect(ctx.ParentSessionKey).toBe("agent:support:slack:channel:C1");
   });
 
-  it("keeps replies in channel root when message is not threaded", async () => {
+  it("keeps replies in channel root when message is not threaded (replyToMode off)", async () => {
     replyMock.mockResolvedValue({ text: "root reply" });
+    config = {
+      messages: {
+        responsePrefix: "PFX",
+        ackReaction: "👀",
+        ackReactionScope: "group-mentions",
+      },
+      slack: {
+        dm: { enabled: true, policy: "open", allowFrom: ["*"] },
+        replyToMode: "off",
+      },
+    };
+
+    const controller = new AbortController();
+    const run = monitorSlackProvider({
+      botToken: "bot-token",
+      appToken: "app-token",
+      abortSignal: controller.signal,
+    });
+
+    await waitForEvent("message");
+    const handler = getSlackHandlers()?.get("message");
+    if (!handler) throw new Error("Slack message handler not registered");
+
+    await handler({
+      event: {
+        type: "message",
+        user: "U1",
+        text: "hello",
+        ts: "789",
+        channel: "C1",
+        channel_type: "im",
+      },
+    });
+
+    await flush();
+    controller.abort();
+    await run;
+
+    expect(sendMock).toHaveBeenCalledTimes(1);
+    expect(sendMock.mock.calls[0][2]).toMatchObject({ threadTs: undefined });
+  });
+
+  it("threads first reply when replyToMode is first and message is not threaded", async () => {
+    replyMock.mockResolvedValue({ text: "first reply" });
     config = {
       messages: {
         responsePrefix: "PFX",
@@ -642,7 +686,8 @@ describe("monitorSlackProvider tool results", () => {
     await run;
 
     expect(sendMock).toHaveBeenCalledTimes(1);
-    expect(sendMock.mock.calls[0][2]).toMatchObject({ threadTs: undefined });
+    // First reply starts a thread under the incoming message
+    expect(sendMock.mock.calls[0][2]).toMatchObject({ threadTs: "789" });
   });
 
   it("forces thread replies when replyToId is set", async () => {
diff --git a/src/slack/monitor.ts b/src/slack/monitor.ts
index 6a25a22b8..b8773316c 100644
--- a/src/slack/monitor.ts
+++ b/src/slack/monitor.ts
@@ -1110,7 +1110,7 @@ export async function monitorSlackProvider(opts: MonitorSlackOpts = {}) {
             accountId: account.accountId,
             runtime,
             textLimit,
-            threadTs: effectiveThreadTs,
+            replyThreadTs: effectiveThreadTs,
           });
           hasRepliedRef.value = true;
         },