From bb43c7b89fbfe22e67253c736b74ed53d2f82eb1 Mon Sep 17 00:00:00 2001
From: lawrence3699 <lawrence3699@users.noreply.github.com>
Date: Wed, 22 Apr 2026 11:44:23 +1000
Subject: [PATCH] fix(mattermost): suppress reasoning previews

---
 .../mattermost/src/mattermost/monitor.test.ts | 23 +++++++++++++++++++
 .../mattermost/src/mattermost/monitor.ts      |  7 ++++--
 .../src/mattermost/reply-delivery.ts          |  4 ++--
 3 files changed, 30 insertions(+), 4 deletions(-)

diff --git a/extensions/mattermost/src/mattermost/monitor.test.ts b/extensions/mattermost/src/mattermost/monitor.test.ts
index 663d7f0a95e..27965ac0417 100644
--- a/extensions/mattermost/src/mattermost/monitor.test.ts
+++ b/extensions/mattermost/src/mattermost/monitor.test.ts
@@ -252,6 +252,29 @@ describe("shouldClearMattermostDraftPreview", () => {
 });
 
 describe("deliverMattermostReplyWithDraftPreview", () => {
+  it("suppresses reasoning-prefixed finals before preview finalization", async () => {
+    const draftStream = createDraftStreamMock();
+    const deliverFinal = vi.fn(async () => {});
+
+    await deliverMattermostReplyWithDraftPreview({
+      payload: { text: "  \n Reasoning:\n_hidden_" } as never,
+      info: { kind: "final" },
+      client: createMattermostClientMock(),
+      draftStream,
+      effectiveReplyToId: "thread-root-1",
+      resolvePreviewFinalText: (text) => text?.trim(),
+      previewState: { finalizedViaPreviewPost: false },
+      logVerboseMessage: vi.fn(),
+      deliverFinal,
+    });
+
+    expect(deliverFinal).not.toHaveBeenCalled();
+    expect(draftStream.flush).not.toHaveBeenCalled();
+    expect(draftStream.discardPending).not.toHaveBeenCalled();
+    expect(draftStream.clear).not.toHaveBeenCalled();
+    expect(updateMattermostPostSpy).not.toHaveBeenCalled();
+  });
+
   it("deletes the preview after a successful normal final send", async () => {
     const draftStream = createDraftStreamMock();
     const deliverFinal = vi.fn(async () => {});
diff --git a/extensions/mattermost/src/mattermost/monitor.ts b/extensions/mattermost/src/mattermost/monitor.ts
index 83ea786ad98..090a12ac889 100644
--- a/extensions/mattermost/src/mattermost/monitor.ts
+++ b/extensions/mattermost/src/mattermost/monitor.ts
@@ -55,7 +55,10 @@ import {
   type MattermostWebSocketFactory,
 } from "./monitor-websocket.js";
 import { runWithReconnect } from "./reconnect.js";
-import { deliverMattermostReplyPayload } from "./reply-delivery.js";
+import {
+  deliverMattermostReplyPayload,
+  shouldSuppressMattermostReasoningReply,
+} from "./reply-delivery.js";
 import type {
   ChannelAccountSnapshot,
   ChatType,
@@ -289,7 +292,7 @@ type MattermostDraftPreviewDeliverParams = {
 export async function deliverMattermostReplyWithDraftPreview(
   params: MattermostDraftPreviewDeliverParams,
 ): Promise<void> {
-  if (params.payload.isReasoning) {
+  if (shouldSuppressMattermostReasoningReply(params.payload)) {
     return;
   }
 
diff --git a/extensions/mattermost/src/mattermost/reply-delivery.ts b/extensions/mattermost/src/mattermost/reply-delivery.ts
index 6ec685b4b33..6fd10d8fd6c 100644
--- a/extensions/mattermost/src/mattermost/reply-delivery.ts
+++ b/extensions/mattermost/src/mattermost/reply-delivery.ts
@@ -26,7 +26,7 @@ type SendMattermostMessage = (
 
 const REASONING_PREFIX = "reasoning:";
 
-function shouldSuppressReasoningReply(payload: ReplyPayload): boolean {
+export function shouldSuppressMattermostReasoningReply(payload: ReplyPayload): boolean {
   if (payload.isReasoning === true) {
     return true;
   }
@@ -49,7 +49,7 @@ export async function deliverMattermostReplyPayload(params: {
   tableMode: MarkdownTableMode;
   sendMessage: SendMattermostMessage;
 }): Promise<void> {
-  if (shouldSuppressReasoningReply(params.payload)) {
+  if (shouldSuppressMattermostReasoningReply(params.payload)) {
     return;
   }
   const reply = resolveSendableOutboundReplyParts(params.payload, {