fix(mattermost): carry thread context to non-inbound reply paths (#44283)

Merged via squash.

Prepared head SHA: 2846a6cfa9
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/channel.test.ts

@@ -355,6 +355,53 @@ describe("mattermostPlugin", () => {
         }),
       );
     });
+
+    it("uses threadId as fallback when replyToId is absent (sendText)", async () => {
+      const sendText = mattermostPlugin.outbound?.sendText;
+      if (!sendText) {
+        return;
+      }
+
+      await sendText({
+        to: "channel:CHAN1",
+        text: "hello",
+        accountId: "default",
+        threadId: "post-root",
+      } as any);
+
+      expect(sendMessageMattermostMock).toHaveBeenCalledWith(
+        "channel:CHAN1",
+        "hello",
+        expect.objectContaining({
+          accountId: "default",
+          replyToId: "post-root",
+        }),
+      );
+    });
+
+    it("uses threadId as fallback when replyToId is absent (sendMedia)", async () => {
+      const sendMedia = mattermostPlugin.outbound?.sendMedia;
+      if (!sendMedia) {
+        return;
+      }
+
+      await sendMedia({
+        to: "channel:CHAN1",
+        text: "caption",
+        mediaUrl: "https://example.com/image.png",
+        accountId: "default",
+        threadId: "post-root",
+      } as any);
+
+      expect(sendMessageMattermostMock).toHaveBeenCalledWith(
+        "channel:CHAN1",
+        "caption",
+        expect.objectContaining({
+          accountId: "default",
+          replyToId: "post-root",
+        }),
+      );
+    });
   });
 
   describe("config", () => {

extensions/mattermost/src/channel.ts

@@ -390,21 +390,30 @@ export const mattermostPlugin: ChannelPlugin<ResolvedMattermostAccount> = {
       }
       return { ok: true, to: trimmed };
     },
-    sendText: async ({ cfg, to, text, accountId, replyToId }) => {
+    sendText: async ({ cfg, to, text, accountId, replyToId, threadId }) => {
       const result = await sendMessageMattermost(to, text, {
         cfg,
         accountId: accountId ?? undefined,
-        replyToId: replyToId ?? undefined,
+        replyToId: replyToId ?? (threadId != null ? String(threadId) : undefined),
       });
       return { channel: "mattermost", ...result };
     },
-    sendMedia: async ({ cfg, to, text, mediaUrl, mediaLocalRoots, accountId, replyToId }) => {
+    sendMedia: async ({
+      cfg,
+      to,
+      text,
+      mediaUrl,
+      mediaLocalRoots,
+      accountId,
+      replyToId,
+      threadId,
+    }) => {
       const result = await sendMessageMattermost(to, text, {
         cfg,
         accountId: accountId ?? undefined,
         mediaUrl,
         mediaLocalRoots,
-        replyToId: replyToId ?? undefined,
+        replyToId: replyToId ?? (threadId != null ? String(threadId) : undefined),
       });
       return { channel: "mattermost", ...result };
     },