feat(mattermost): add replyToMode support (off | first | all) (#29587)

Merged via squash.

Prepared head SHA: 4a67791f53
Co-authored-by: teconomix <6959299+teconomix@users.noreply.github.com>
Co-authored-by: mukhtharcm <56378562+mukhtharcm@users.noreply.github.com>
Reviewed-by: @mukhtharcm

extensions/mattermost/src/config-schema.test.ts

@@ -1,7 +1,7 @@
 import { describe, expect, it } from "vitest";
 import { MattermostConfigSchema } from "./config-schema.js";
 
-describe("MattermostConfigSchema SecretInput", () => {
+describe("MattermostConfigSchema", () => {
   it("accepts SecretRef botToken at top-level", () => {
     const result = MattermostConfigSchema.safeParse({
       botToken: { source: "env", provider: "default", id: "MATTERMOST_BOT_TOKEN" },
@@ -21,4 +21,29 @@ describe("MattermostConfigSchema SecretInput", () => {
     });
     expect(result.success).toBe(true);
   });
+
+  it("accepts replyToMode", () => {
+    const result = MattermostConfigSchema.safeParse({
+      replyToMode: "all",
+    });
+    expect(result.success).toBe(true);
+  });
+
+  it("rejects unsupported direct-message reply threading config", () => {
+    const result = MattermostConfigSchema.safeParse({
+      dm: {
+        replyToMode: "all",
+      },
+    });
+    expect(result.success).toBe(false);
+  });
+
+  it("rejects unsupported per-chat-type reply threading config", () => {
+    const result = MattermostConfigSchema.safeParse({
+      replyToModeByChatType: {
+        direct: "all",
+      },
+    });
+    expect(result.success).toBe(false);
+  });
 });