diff --git a/extensions/mattermost/src/mattermost/monitor.test.ts b/extensions/mattermost/src/mattermost/monitor.test.ts
index 3394dc2c995..49f71e46d9a 100644
--- a/extensions/mattermost/src/mattermost/monitor.test.ts
+++ b/extensions/mattermost/src/mattermost/monitor.test.ts
@@ -3,6 +3,7 @@ import { describe, expect, it, vi } from "vitest";
 import type { OpenClawConfig } from "../../runtime-api.js";
 import { resolveMattermostAccount } from "./accounts.js";
 import {
+  buildMattermostModelPickerSelectMessageSid,
   evaluateMattermostMentionGate,
   MattermostRetryableInboundError,
   processMattermostReplayGuardedPost,
@@ -378,6 +379,41 @@ describe("processMattermostReplayGuardedPost", () => {
   });
 });
 
+describe("buildMattermostModelPickerSelectMessageSid", () => {
+  it("stays stable for the same picker selection", () => {
+    expect(
+      buildMattermostModelPickerSelectMessageSid({
+        postId: "post-1",
+        provider: "OpenAI",
+        model: " GPT-5 ",
+      }),
+    ).toBe("interaction:post-1:select:openai/gpt-5");
+    expect(
+      buildMattermostModelPickerSelectMessageSid({
+        postId: "post-1",
+        provider: "openai",
+        model: "gpt-5",
+      }),
+    ).toBe("interaction:post-1:select:openai/gpt-5");
+  });
+
+  it("keeps different model selections distinct", () => {
+    expect(
+      buildMattermostModelPickerSelectMessageSid({
+        postId: "post-1",
+        provider: "openai",
+        model: "gpt-5",
+      }),
+    ).not.toBe(
+      buildMattermostModelPickerSelectMessageSid({
+        postId: "post-1",
+        provider: "openai",
+        model: "gpt-4.1",
+      }),
+    );
+  });
+});
+
 describe("resolveMattermostReactionChannelId", () => {
   it("prefers broadcast channel_id when present", () => {
     expect(
diff --git a/extensions/mattermost/src/mattermost/monitor.ts b/extensions/mattermost/src/mattermost/monitor.ts
index bf1279596bc..811db94ded9 100644
--- a/extensions/mattermost/src/mattermost/monitor.ts
+++ b/extensions/mattermost/src/mattermost/monitor.ts
@@ -139,6 +139,16 @@ export class MattermostRetryableInboundError extends Error {
   }
 }
 
+export function buildMattermostModelPickerSelectMessageSid(params: {
+  postId: string;
+  provider: string;
+  model: string;
+}): string {
+  const provider = normalizeLowercaseStringOrEmpty(params.provider);
+  const model = normalizeLowercaseStringOrEmpty(params.model);
+  return `interaction:${params.postId}:select:${provider}/${model}`;
+}
+
 function buildMattermostInboundReplayKeys(params: {
   accountId: string;
   messageIds: string[];
@@ -698,6 +708,7 @@ export async function monitorMattermostProvider(opts: MonitorMattermostOpts = {}
     roomLabel: string;
     teamId?: string;
     postId: string;
+    messageSid?: string;
     effectiveReplyToId?: string;
     deliverReplies?: boolean;
   }): Promise<string> => {
@@ -731,7 +742,7 @@ export async function monitorMattermostProvider(opts: MonitorMattermostOpts = {}
       SenderId: params.senderId,
       Provider: "mattermost" as const,
       Surface: "mattermost" as const,
-      MessageSid: `interaction:${params.postId}:${Date.now()}`,
+      MessageSid: params.messageSid ?? `interaction:${params.postId}:${Date.now()}`,
       ReplyToId: params.effectiveReplyToId,
       MessageThreadId: params.effectiveReplyToId,
       Timestamp: Date.now(),
@@ -1023,6 +1034,11 @@ export async function monitorMattermostProvider(opts: MonitorMattermostOpts = {}
           roomLabel,
           teamId,
           postId: params.payload.post_id,
+          messageSid: buildMattermostModelPickerSelectMessageSid({
+            postId: params.payload.post_id,
+            provider: pickerState.provider,
+            model: pickerState.model,
+          }),
           effectiveReplyToId: threadContext.effectiveReplyToId,
           deliverReplies: true,
         });