feat: suppress Discord link embed previews on bot messages

Add MessageFlags.SuppressEmbeds to all send() calls so URLs in
agent responses don't generate large preview cards.

src/channels/discord.test.ts

@@ -98,6 +98,7 @@ vi.mock('discord.js', () => {
     Client: MockClient,
     Events,
     GatewayIntentBits,
+    MessageFlags: { SuppressEmbeds: 1 << 2 },
     TextChannel,
   };
 });
@@ -760,10 +761,12 @@ describe('DiscordChannel', () => {
       expect(mockChannel.send).toHaveBeenNthCalledWith(1, {
         content: 'x'.repeat(2000),
         files: undefined,
+        flags: 1 << 2,
       });
       expect(mockChannel.send).toHaveBeenNthCalledWith(2, {
         content: 'x'.repeat(1000),
         files: undefined,
+        flags: 1 << 2,
       });
     });
   });

src/channels/discord.ts

@@ -7,6 +7,7 @@ import {
   Events,
   GatewayIntentBits,
   Message,
+  MessageFlags,
   TextChannel,
 } from 'discord.js';
 
@@ -457,6 +458,7 @@ export class DiscordChannel implements Channel {
         await textChannel.send({
           content: cleaned || undefined,
           files: files.length > 0 ? files : undefined,
+          flags: MessageFlags.SuppressEmbeds,
         });
       } else {
         // Send text in chunks, attach images to the first chunk
@@ -465,6 +467,7 @@ export class DiscordChannel implements Channel {
           await textChannel.send({
             content: chunk,
             files: i === 0 && files.length > 0 ? files : undefined,
+            flags: MessageFlags.SuppressEmbeds,
           });
         }
       }